Color balancing systems and methods

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This application claims priority to U.S. provisional application Ser. No. 60/879,497, filed Jan. 8, 2007, which is incorporated herein by reference.

BACKGROUND

0002I. Field

0003The field of the present invention relates to color balancing in a display system.

0004II. Background

0005In many applications, it is desirable that the white point of a projection system be as close as possible to the blackbody curve. When the intrinsic white point of a display does not fall on a desired location on the blackbody curve, compensation with other components in the system is termed “color balancing.”

0006What is desired are improved systems and methods for color balancing.

BRIEF DESCRIPTION OF THE DRAWINGS

0007The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

0008<figref idref="DRAWINGS">FIG. 1A</figref> schematically depicts a micro-display projection system according to an example embodiment utilizing a light source, color wheel, a collection optics assembly, matching optics assembly, micro-display imager, system control electronics, projection optics assembly, and screen.

0009<figref idref="DRAWINGS">FIG. 1B</figref> is a functional block diagram of a <figref idref="DRAWINGS">FIG. 1A</figref> projection system utilizing a single color wheel, matching optics assembly, and micro-display imager, according to an example embodiment.

0010<figref idref="DRAWINGS">FIGS. 2A and 2B</figref> each show an example color wheel according to an example embodiment.

0011<figref idref="DRAWINGS">FIG. 3</figref> shows the spectrum of an example light source.

0012<figref idref="DRAWINGS">FIG. 4</figref> shows the 1931-CIE color gamut chart and the blackbody curve on the standard x/y chromaticity coordinate plane.

0013<figref idref="DRAWINGS">FIG. 5A</figref> shows the transmission spectrum of an example RGBM color wheel.

0014<figref idref="DRAWINGS">FIG. 5B</figref> shows example embodiments of an RGBM color wheel on the 1931-CIE chromaticity chart and associated white points.

0015<figref idref="DRAWINGS">FIG. 5C</figref> shows example embodiments of an RGBM color wheel on the 1931-CIE chromaticity chart and associated white points.

0016<figref idref="DRAWINGS">FIG. 6A</figref> shows an example embodiment of an RGB color wheel on the 1931-CIE chromaticity chart and its associated white point.

0017<figref idref="DRAWINGS">FIG. 6B</figref> shows the transmission spectrum of the RGB color wheel depicted in <figref idref="DRAWINGS">FIG. 6A</figref>.

0018<figref idref="DRAWINGS">FIG. 7</figref> shows the spectrum of an example light source.

0019<figref idref="DRAWINGS">FIG. 8</figref> shows an example color wheel layout.

0020<figref idref="DRAWINGS">FIG. 9A</figref> shows the transmission spectrum of an example RGBCYM color wheel.

0021<figref idref="DRAWINGS">FIG. 9B</figref> shows the transmission spectrum of an example RGBCYM color wheel.

0022<figref idref="DRAWINGS">FIG. 10A</figref> shows an example RGBCYM color wheel on the 1931-CIE chromaticity chart and associated white point.

0023<figref idref="DRAWINGS">FIG. 10B</figref> shows an example RGBCYM color wheel on the 1931-CIE chromaticity chart and associated white point.

0024<figref idref="DRAWINGS">FIG. 11</figref> is a cross-section and schematic view of an example electrodeless plasma lamp that may be used as a light source in a projection system according to an example embodiment.

0025<figref idref="DRAWINGS">FIG. 12</figref> is a cross-section and schematic view of an example electrodeless plasma lamp that may be used as a light source in a projection system according to an example embodiment.

DESCRIPTION OF EXAMPLE EMBODIMENTS

0026While the present invention is open to various modifications and alternative constructions, the embodiments shown in the drawings will be described by way of example herein in detail. It is to be understood, however, there is no intention to limit the invention to the particular forms disclosed. On the contrary, it is intended that the invention cover all modifications, equivalences and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

0027Referring to <figref idref="DRAWINGS">FIG. 1A</figref>, an example micro-display projection system <b>10</b> includes a light source <b>20</b>, color wheel <b>30</b>, collection optics assembly <b>40</b>, matching optics assembly <b>50</b>, micro-display imager <b>60</b>, system control electronics (SCE) <b>70</b>, projection optics assembly <b>80</b>, and screen <b>90</b>. Light source <b>20</b> may be an electrodeless plasma lamp that emits broad-spectrum white light to color wheel <b>30</b> which may be divided into red-, green- and blue- and magenta-filter sectors. Other color segments may also be used, such as Cyan and Yellow as described further below. Some color wheels may also include other color segments, such as a clear (white transmissive) color segment, and other types of color filters may be used in other embodiments. Typically, color wheel <b>30</b> is driven at a preselected rotation rate (e.g., about 120 or 240 rotations per second in some embodiments) by the system control electronics <b>70</b>; its rotational phase (angular position) is fed back via two-way link <b>72</b>. In this example, rapidly alternating primary-color light exiting the color wheel reaches micro-display imager <b>60</b> after passing through matching optics assembly <b>50</b>. In this example embodiment, the system control electronics <b>70</b> performs the function of translating the frame data encoding the image to be projected into detailed commands for the micro-display imager <b>60</b>. For each color primary (e.g., R, G, B or M) a set of pixel elements on the micro-display imager <b>60</b> is commanded by the system control electronics <b>70</b> via a one-way link <b>74</b> to spatially modulate that color, forming a pattern that is the monochromatic primary component of the image being displayed. Algorithms executed by the SCE <b>70</b> for generating the desired color for a pixel from primary components include, for example, BrilliantColor™ from Texas Instruments. In some example embodiments, the transitional portion or spoke between adjacent colors on the color wheel may be processed as secondary color elements to boost brightness.

0028In this example embodiment, each pattern consists of a two-dimensional array of sub-pixels for each color, of varying intensity. The micro-display imager <b>60</b> may selectively control the light projected to the screen <b>90</b> for each sub-pixel. With some micro-display imagers <b>60</b>, the light may be selectively transmitted through the micro-display imager to the screen <b>90</b> (as suggested by the arrangement shown in <figref idref="DRAWINGS">FIG. 1</figref>). Other micro-display imagers <b>60</b> may selectively reflect light to the screen <b>90</b>.

0029One type of micro-display imager that may be used in example embodiments is a DLP® microdisplay. DLP® microdsplays use a grid of micromirrors to selectively reflect light to the screen <b>90</b>. These micromirrors form the pixel elements of the microdisplay. In example embodiments, there may be one mirror for each pixel location and each mirror can be tilted very rapidly. Tilting one way allows light to reflect toward the screen, while tilting another way allows the light to be reflected such that the light does not reach the screen. The color shade of each pixel is controlled through a dithering technique that varies the amount of time each pixel reflects light to the screen. In a DLP®-based projection system, intensity typically is controlled using pulse-width modulation (PWM) which achieves proportional modulation of the intensity of any particular pixel by controlling, for each displayed frame, the fraction of time spent in either the “ON” or “OFF” state. That is, modulation of the pixels is quantized, and the “ON/OFF” time ratio of each pixel is varied for each color segment of the color wheel, creating the perception of continuous intensity variation when integrated by an observer's much slower visual response. The ON and OFF states correspond to deflections of micro-mirrors forming the pixels, directing light toward or away from, respectively, the projection optical-axis. The modulation waveform on each pixel is typically limited in duration by two factors. At the short extreme is the response time of the micro-mirror; at the long extreme is the refresh rate of the displayed image. The PWM signal typically is a digitally synthesized pulse spanning a preselected range between these two limits, thereby defining a quantized set of achievable intensity modulation points for a given light brightness impinging on the DLP imager. As the color wheel rotates, the micromirror pixel elements sequentially reflect a set of pixels (one for each color segment) to the screen, with the intensity of each pixel element controlled by PWM. Although they are projected sequentially as the color wheel rotates, the sets of pixels for each color segment appear as a single combined image projected on the screen.

0030In an example embodiment, the amount of PWM for each color segment is controlled by the number of bits used for that color segment. These bits are provided to the system control electronics <b>70</b> via input <b>71</b> or may be generated by the system control electronics <b>70</b> based on other inputs. The system control electronics <b>70</b> determines the rotational phase of the color wheel and desired PWM for the corresponding color segment (based on the desired color of the pixel) and controls the micro-display imager <b>60</b> via link <b>74</b> to provide the appropriate PWM for the color segment. For example, the primary color segment for each pixel may have an 8 bit value, providing for 256 values (e.g., 0-255) for the PWM for that color segment. In example embodiments, each primary color segment has the same number of bits (and corresponding levels of PWM). In other examples, the number of bits may be different for different color segments and may depend on the size of the color segment. Smaller color segments may not be able to accommodate as many levels of PWM. In some embodiments, spokes or small color boost segments are processed with a smaller number of bits.

0031In other types of micro-display imagers that may be used in example embodiments, e.g., liquid crystal display (LCD) spatial-light modulators, the ON and OFF states of the pixel elements correspond, respectively, to states of high and low optical transmission through the imager. In this example embodiment, a single primary-color sub-image is projected onto a screen after passing through appropriate projection optics. In example projection system <b>10</b>, these are screen <b>90</b> and projection optics assembly <b>80</b>.

0032Another type of micro-display imager that may be used in example embodiments is liquid crystal on silicon (LCOS). LCOS microdisplays create pixels by covering a reflective silicon chip with crystal material arranged in a grid pattern. Like LCDs, the orientation of the crystals is controlled by applying current to control the amount of light that is reflected from the chip's surface at each pixel location. This controls the ON and OFF states of the pixel elements. The reflected light is then magnified and focused on the inside surface of the screen <b>90</b> to form the picture.

0033In some example embodiments, a color wheel or other color filter is used with red, green and blue segments as well as an additional magenta segment. <figref idref="DRAWINGS">FIGS. 2A and 2B</figref> each show an example red, blue, green and magenta color wheel that may be used in example embodiments of a projection display system. Red, green and blue are referred to as additive primaries. Cyan, yellow and magenta are referred to as subtractive primaries. In the example color wheels of <figref idref="DRAWINGS">FIGS. 2A and 2B</figref>, the magenta color segment is the only subtractive primary. The color wheels do not include Cyan or Yellow color segments. <figref idref="DRAWINGS">FIG. 2A</figref> shows a color wheel with two blue segments and one segment each of red, green and magenta. Blue is the largest portion of the color wheel and is separate into two segments. <figref idref="DRAWINGS">FIG. 2B</figref> shows a color wheel with two segments each of red, blue and green and one segment of magenta. Once again, blue is the largest portion of the color wheel. In other examples, the color wheel (or other color filter) may consist of different sequences of R,G,B,M segments—for example, RGBM, RBGBM, RGBMRGB, etc. Those skilled in the art will recognize that the design factors involved are the desire to minimize color breakup and the need to maintain the minimum color segment size consistent with the micro-display control's quantization.

0034While spokes could be processed as additional secondary color elements (or small color boost segments could be added to the color wheel) with one or a few bits of PWM, in the examples of <figref idref="DRAWINGS">FIGS. 2A and 2B</figref>, the magenta segment is similarly sized to the additive primary segments and may be processed using the same number of bits (and levels of PWM) as some or all of the additive primary color segments. As a result, the magenta segment may be treated by the system control electronics as a fully primary color segment for color balancing (e.g., with full bit depth). For example, 8 bits (256 values) of PWM modulation may be used for the magenta segment in this example. In some examples, the magenta segment is sized to be large enough for the full range of PWM to be used for the magenta color segment as for the red, green and blue color segments. In some examples, the magenta segment may be 35, 40, 50 or 60 degrees or more of the 360 degree color wheel. In some examples, the duty cycle of the magenta color segment may be from about 0.1 to 0.2 or any range subsumed therein. In some examples, the magenta segment may not be the smallest color segment and at least one additive primary segment may be smaller than the magenta color segment (e.g., the green segment in <figref idref="DRAWINGS">FIG. 2B</figref>).

0035<figref idref="DRAWINGS">FIG. 3</figref> shows an example spectrum for a light source used in a projection display system according to an example embodiment. This spectrum peaks in green (approx 500 nm). A green-peaked spectrum is typical of many metal-halide high intensity discharge lamps, such as an electrodeless plasma lamp using an Indium Bromide fill as the light emitter. Color wheels of the type shown in <figref idref="DRAWINGS">FIGS. 2A and 2B</figref> may be well-suited for color balancing a light source of this type. Magenta is transmissive to red and blue (subtractive to green). The magenta color segment helps compensate for the lower levels of blue and red in the spectrum, while allowing for higher overall brightness compared to a color balanced RGB color wheel. The large blue segments also help compensate for the lower levels of blue in the spectrum.

0036To demonstrate the operating principle behind the color-balancing efficiency of these example embodiments, it is helpful to review the fundamentals of chromaticity diagrams. A “color” may be defined by its full spectrum—that is, intensity as a function of wavelength λ. The spectral representation is difficult to work with directly when considering the span of all colors available to a system, with each possible color represented by a full 2-D graph. Instead, it is helpful to reduce any given spectrum to a pair of coordinates on a plane. An infinite set of possible such representations exist, but the accepted standard is the 1931-CIE chromaticity diagram, which specifies three standard spectra: X_CIE(λ), Y_CIE(λ), Z_CIE(λ), fundamentally arbitrary but loosely corresponding to red, green, and blue colors of moderate saturation. Given any arbitrary spectrum f(λ), the prescription to arrive at the corresponding color coordinates (x_f, y_f) is to compute the vector V(f(λ)):

0000<maths id="MATH-US-00001" num="00001"><math overflow="scroll"><mrow><mrow><munder><mi>V</mi><mi>_</mi></munder><mo></mo><mrow><mo>(</mo><mrow><mi>f</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo>)</mo></mrow></mrow><mo>=</mo><mrow><mo>[</mo><mtable><mtr><mtd><mrow><msub><mo>∫</mo><mi>λ</mi></msub><mo></mo><mrow><mrow><mi>f</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo></mo><mrow><msub><mi>X</mi><mi>CIE</mi></msub><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo></mo><mstyle><mspace width="0.2em" height="0.2ex" /></mstyle><mo></mo><mrow><mo></mo><mi>λ</mi></mrow></mrow></mrow></mtd></mtr><mtr><mtd><mrow><msub><mo>∫</mo><mi>λ</mi></msub><mo></mo><mrow><mrow><mi>f</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo></mo><mrow><msub><mi>Y</mi><mi>CIE</mi></msub><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo></mo><mstyle><mspace width="0.2em" height="0.2ex" /></mstyle><mo></mo><mrow><mo></mo><mi>λ</mi></mrow></mrow></mrow></mtd></mtr><mtr><mtd><mrow><msub><mo>∫</mo><mi>λ</mi></msub><mo></mo><mrow><mrow><mi>f</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo></mo><mrow><msub><mi>Z</mi><mi>CIE</mi></msub><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo></mo><mstyle><mspace width="0.2em" height="0.2ex" /></mstyle><mo></mo><mrow><mo></mo><mi>λ</mi></mrow></mrow></mrow></mtd></mtr></mtable><mo>]</mo></mrow></mrow></math></maths>

0000then form the coordinates from the dot product ratios:

0000<maths id="MATH-US-00002" num="00002"><math overflow="scroll"><mrow><msub><mi>x</mi><mi>f</mi></msub><mo>=</mo><mfrac><mrow><mrow><mo>[</mo><mtable><mtr><mtd><mn>1</mn></mtd><mtd><mn>0</mn></mtd><mtd><mn>0</mn></mtd></mtr></mtable><mo>]</mo></mrow><mo></mo><mrow><munder><mi>V</mi><mi>_</mi></munder><mo></mo><mrow><mo>(</mo><mrow><mi>f</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo>)</mo></mrow></mrow></mrow><mrow><mrow><mo>[</mo><mtable><mtr><mtd><mn>1</mn></mtd><mtd><mn>1</mn></mtd><mtd><mn>1</mn></mtd></mtr></mtable><mo>]</mo></mrow><mo></mo><mrow><munder><mi>V</mi><mi>_</mi></munder><mo></mo><mrow><mo>(</mo><mrow><mi>f</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo>)</mo></mrow></mrow></mrow></mfrac></mrow></math></maths><maths id="MATH-US-00002-2" num="00002.2"><math overflow="scroll"><mrow><msub><mi>y</mi><mi>f</mi></msub><mo>=</mo><mfrac><mrow><mrow><mo>[</mo><mtable><mtr><mtd><mn>0</mn></mtd><mtd><mn>1</mn></mtd><mtd><mn>0</mn></mtd></mtr></mtable><mo>]</mo></mrow><mo></mo><mrow><munder><mi>V</mi><mi>_</mi></munder><mo></mo><mrow><mo>(</mo><mrow><mi>f</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo>)</mo></mrow></mrow></mrow><mrow><mrow><mo>[</mo><mtable><mtr><mtd><mn>1</mn></mtd><mtd><mn>1</mn></mtd><mtd><mn>1</mn></mtd></mtr></mtable><mo>]</mo></mrow><mo></mo><mrow><munder><mi>V</mi><mi>_</mi></munder><mo></mo><mrow><mo>(</mo><mrow><mi>f</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo>)</mo></mrow></mrow></mrow></mfrac></mrow></math></maths>

0000(The corresponding z_fis redundant from the relation z_f=1−x_f−y_fand reflects the fact that brightness is normalized on the plane.)

0037<figref idref="DRAWINGS">FIG. 4</figref> shows two features represented on the 1931-CIE diagram of relevance to example embodiments. When f(λ) is monochromatic (the Dirac-delta function δ(λ)), the truncated oval <b>1</b> is traced out. For λ spanning the entire visible wavelength range (typically taken to be 400-700 nm), this figure bounds all possible colors that can exist on the x/y plane. When f(λ) is the blackbody spectrum representing emission from an ideal blackbody at some temperature T, the arc <b>2</b> is traced out. The span shown here corresponds roughly to the temperature span 1500K to 10000K. Because the standard 1931-CIE spectras X_CIE(λ), Y_CIE(λ); Z_CIE(λ) tail-off to zero past 700 nm, blackbody temperatures much higher than 10000K are not usefully depicted—they mathematically collapse to a small arc segment near coordinates (0.25, 0.25).

0038The following describes an example approach for color balancing using a red, blue, green and magenta color wheel according to example embodiments. Define the spectrum of the lamp to be the function S(λ). Further, define the fractional duty-cycle of the color wheel segments to be T_R, T_G, T_B, T_Mfor red, green, blue, and magenta segments respectively. Note the (typically small) absorption of each of the dichroic filters in the color segments is intentionally not accounted for in this example for simplicity, although other embodiments may take this into account. Therefore in an RGB wheel, T_R+T_G+T_B=1, while in the RGBM wheel, T_R+T_G+T_B+T_M=1. Finally, define the actual transmission spectra of the color wheel segments to be R(λ), G(λ), B(λ), and M(λ) for red, green, blue, and magenta segments respectively. For simplicity of discussion, assume that all elements of the projection system are color neutral except for the lamp and the color-wheel (this is largely true in reality). The system white spectrum can be defined as the spectrum that results when the micro-display is commanded to transmit/reflect all the light available from each primary. The system white point is then the (x, y) coordinates of the system white spectrum. Additionally, we can define the total light transmission through the color wheel to be the total area under the white spectrum. We therefore have, for an RGB and RGBM system using the same lamp, the following definitions for the white spectrum and total transmission:

0000<maths id="MATH-US-00003" num="00003"><math overflow="scroll"><mrow><mrow><msub><mi>W</mi><mi>RGB</mi></msub><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo>=</mo><mrow><mrow><mi>S</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo></mo><mrow><mo>[</mo><mrow><mrow><msub><mi>T</mi><mi>R</mi></msub><mo></mo><mrow><mi>R</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow></mrow><mo>+</mo><mrow><msub><mi>T</mi><mi>G</mi></msub><mo></mo><mrow><mi>G</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow></mrow><mo>+</mo><mrow><msub><mi>T</mi><mi>B</mi></msub><mo></mo><mrow><mi>B</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow></mrow></mrow><mo>]</mo></mrow></mrow></mrow></math></maths><maths id="MATH-US-00003-2" num="00003.2"><math overflow="scroll"><mrow><msub><mi>B</mi><mi>RGB</mi></msub><mo>=</mo><mrow><msub><mo>∫</mo><mi>λ</mi></msub><mo></mo><mrow><mrow><msub><mi>W</mi><mi>RGB</mi></msub><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo></mo><mstyle><mspace width="0.2em" height="0.2ex" /></mstyle><mo></mo><mrow><mo></mo><mi>λ</mi></mrow></mrow></mrow></mrow></math></maths><maths id="MATH-US-00003-3" num="00003.3"><math overflow="scroll"><mrow><mrow><msub><mi>W</mi><mi>RGBM</mi></msub><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo>=</mo><mrow><mrow><mi>S</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo></mo><mrow><mo>[</mo><mrow><mrow><msub><mi>T</mi><mi>R</mi></msub><mo></mo><mrow><mi>R</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow></mrow><mo>+</mo><mrow><msub><mi>T</mi><mi>G</mi></msub><mo></mo><mrow><mi>G</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow></mrow><mo>+</mo><mrow><msub><mi>T</mi><mi>B</mi></msub><mo></mo><mrow><mi>B</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow></mrow><mo>+</mo><mrow><msub><mi>T</mi><mi>M</mi></msub><mo></mo><mrow><mi>M</mi><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow></mrow></mrow><mo>]</mo></mrow></mrow></mrow></math></maths><maths id="MATH-US-00003-4" num="00003.4"><math overflow="scroll"><mrow><msub><mi>B</mi><mi>RGBM</mi></msub><mo>=</mo><mrow><msub><mo>∫</mo><mi>λ</mi></msub><mo></mo><mrow><mrow><msub><mi>W</mi><mi>RGBM</mi></msub><mo></mo><mrow><mo>(</mo><mi>λ</mi><mo>)</mo></mrow></mrow><mo></mo><mstyle><mspace width="0.2em" height="0.2ex" /></mstyle><mo></mo><mrow><mo></mo><mi>λ</mi></mrow></mrow></mrow></mrow></math></maths>

0000The process of color balancing to a specific white-point temperature with the color wheel is then seen to be more precisely defined as selecting [T_R, T_G, T_B] or [T_R, T_G, T_B, T_M] such that the corresponding W_RGB(λ) or W_RGBM(λ) have (x,y) coordinates that fall on or as close to as possible the blackbody curve at that temperature. In example embodiments, for green-rich S(λ) similar to that of <figref idref="DRAWINGS">FIG. 3</figref>, and color-balance temperatures useful for projection displays (6000-10000K), when [T_R, T_G, T_B] and [T_R, T_G, T_B, T_M] have been selected for color balance, B_RGBM>B_RGB. That is, the color-balanced RGBM lamp/color-wheel system is brighter than the color-balanced RGB system. In fact, we find that, for the typical lamp spectrum shown in <figref idref="DRAWINGS">FIG. 3</figref>, imposing a practical minimum on T_Gmay renders coloring balancing to the blackbody curve unachievable as described further in connection with <figref idref="DRAWINGS">FIG. 6A</figref> below.

0039<figref idref="DRAWINGS">FIG. 6A</figref> shows an example design of an RBG color wheel on the 1931-CIE chromaticity plane. The spectra of each color segment in this design is shown in <figref idref="DRAWINGS">FIG. 6B</figref>. Corresponding to each of the color segment spectra are the (x/y) coordinates in <figref idref="DRAWINGS">FIG. 6A</figref>; the red segment at 1, blue at 2, and green at 3. In addition, the green segment size conforms to the minimum-segment constraint imposed by an example microdisplay imager PWM algorithm, which in this example is approximately 40 degrees at 14440 RPM wheel rotation speed. Perfect color-balancing at 9000K is not achieved in this example. To come as close as possible to the 9000K blackbody point, the wheel segment duty cycles are [T_R, T_G, T_B]=[0.29, 0.29, 0.42]. The resulting white point is shown on <figref idref="DRAWINGS">FIG. 6A</figref> at <b>4</b>.

0040<figref idref="DRAWINGS">FIG. 5A</figref> shows an example design of an RBGM color wheel according to an example embodiment, with the spectra of each color segment plotted vs. wavelength. Corresponding to each of the color segment spectra are the (x/y) coordinates in <figref idref="DRAWINGS">FIG. 5B</figref>; the red segment at <b>1</b>, blue at <b>2</b>, green at <b>3</b>, and magenta at <b>4</b>. It is a useful property of the chromaticity diagram that the polygon formed by the color segment points <b>5</b> bounds all colors achievable with that color wheel.

0041The spectra in <figref idref="DRAWINGS">FIG. 5A</figref> can be characterized as well by their 50% transmission wavelengths, shown as indices R, G<b>1</b>, G<b>2</b>, B, M<b>1</b>, and M<b>2</b> for the red, green, blue, and magenta segments respectively. In this example, the indices show wavelengths of 598 nm, 493 nm, 591 nm, 487 nm, 486 nm, and 589 nm respectively. In this example, the slope of each transition is such that minimum and maximum transmissions are spaced apart by no more than about 15 nm. This parameter may be varied in other embodiments, and its value may be selected in a tradeoff against the cost of manufacture.

0042One example method for achieving color balance is to vary the duty cycle (and therefore the fractional transmission) of each color segment. For the color wheel spectra shown in <figref idref="DRAWINGS">FIG. 5A</figref> and corresponding vertices in <figref idref="DRAWINGS">FIG. 5B</figref>, the points W<b>7</b>, W<b>8</b>, and W<b>9</b> are white balance points at 7000K, 8000K, and 9000K respectively. The corresponding duty cycles for each color wheel are [T_R, T_G, T_B, T_M]=[0.306 0.25 0.333 0.111], [T_R, T_G, T_B, T_M]=[0.25 0.25 0.356 0.144], and [T_R, T_G, T_B, T_M]=[0.194 0.25 0.389 0.167] respectively. In this example, each segment size is greater than the minimum-segment constraint imposed by an example microdisplay imager PWM algorithm, which in this example is approximately 40 degrees at 14440 RPM wheel rotation speed. It is seen that the magenta wheel segment at <b>4</b> in <figref idref="DRAWINGS">FIG. 5B</figref>, when used as a full color primary in conjunction with the projection system, is effective at balancing the white point onto the blackbody curve at a range of temperatures.

0043In example embodiments, an RGBM color wheel is used to balance a spectrum that peaks in green at a correlated color temperature (CCT) in the range of about 6000-11000K or any range subsumed therein. In example embodiments, the duty cycle for red is in the range of about 0.15 to 0.35 or any range subsumed therein, the duty cycle for green is in the range of about 0.2 to 0.3 or any range subsumed therein, the duty cycle for blue is in the range of about 0.3 to 0.4 or any range subsumed therein and the duty cycle for magenta is in the range of about 0.1 to 0.2 or any range subsumed therein. In example embodiments, the red segment comprises an angle on the color wheel of between about 50 to 120 degrees or any range subsumed therein (which may be a single segment or split among multiple segments), the green segment comprises an angle on the color wheel of between about 60 to 110 degrees or any range subsumed therein (which may be a single segment or split among multiple segments), the blue segment comprises an angle on the color wheel of between about 105 to 150 degrees or any range subsumed therein (which may be a single segment or split among multiple segments) and the magenta segment comprises an angle on the color wheel of between about 35 to 80 degrees or any range subsumed therein (which may be a single segment or split among multiple segments). In some examples, each R, G, B and M color segment is at least 40 degrees. In some examples, the magenta color segment is the only subtractive primary on the color filter or is the only subtractive primary with full bit depth for PWM (e.g., 8 bits or more). In example embodiments, the magenta color segment has 256 or more PWM values. In other examples, the number of PWM values for the magenta color segment is in the range of about 128 to 1024 or any range subsumed therein. In example embodiments, the magenta color segment has the same number of bits (and levels of PWM) as the red color segment, green color segment or blue color segment. In some examples, the red, green, blue and magenta color segments each have a number of PWM values in the range of about 128 to 1024 or any range subsumed therein.

0044Another example method of achieving color balance is to vary the transmission spectra of the segments on the color wheel. We show an example in <figref idref="DRAWINGS">FIG. 5C</figref> of adjusting the magenta segment spectrum, although in general all segments can be adjusted. Like indices refer to like elements in <figref idref="DRAWINGS">FIG. 5B</figref>. The white point on the blackbody curve at 7000K, as indicated by W<b>7</b> in <figref idref="DRAWINGS">FIG. 5C</figref>, corresponds to a magenta spectrum whose 50% transmission points are at 470 nm and 585 nm, referring respectively to M<b>1</b> and M<b>2</b> in <figref idref="DRAWINGS">FIG. 5A</figref> and indicated at M<b>7</b> in <figref idref="DRAWINGS">FIG. 5C</figref>. The white point on the blackbody curve at 8000K, as indicated by W<b>8</b> in <figref idref="DRAWINGS">FIG. 5C</figref>, corresponds to a magenta spectrum whose 50% transmission points are at 486 n m and 589 nm, referring respectively to M<b>1</b> and M<b>2</b> in <figref idref="DRAWINGS">FIG. 5A</figref> and indicated at M<b>8</b> in <figref idref="DRAWINGS">FIG. 5C</figref>.

0045In example embodiments, an RGBM color wheel is used to balance a spectrum that peaks in green at a correlated color temperature (CCT) in the range of about 6000-11000K or any range subsumed therein. In example embodiments, the 50% transmission points of a magenta color filter segment are, at the low end, in the range of about 450 nm to 510 nm or any range subsumed therein and, at the high end, in the range of about 550 nm to 625 nm or any range subsumed therein. In some embodiments, a color wheel with 50% transmission points in any of the above ranges may be combined with duty cycles for red, green, blue and magenta in any of the ranges described above to achieve color balancing at a desired correlated color temperature (CCT) in the range of about 6000-11000K or any range subsumed therein. These are examples only and other 50% transmission points and duty cycles may be used in other embodiments.

0046The use of RGBM wheel segments is useful for the plasma emission spectrum shown in <figref idref="DRAWINGS">FIG. 3</figref>, which is typical of a bulb fill material comprising InBr or other Indium halide. The use of RGBM wheel segments is also useful for other metal halide emitters or other fills producing a green rich spectrum. Another useful fill material in high intensity discharge lamps (including, for example, electrodeless plasma lamps) comprises aluminum halide and holmium halide. An example is Aluminum Bromide and Holmium Bromide (AlBr₃/HoBr₃). An example emission spectrum for this fill is shown in <figref idref="DRAWINGS">FIG. 7</figref>. Because this spectrum is flatter in the shorter wavelengths, a full RGBCYM color wheel is more effective in achieving color-balancing onto the blackbody curve. These examples may also be useful with other metal halide fills that include a combination of metal halides that provide more blue (such as AlBr₃) and more red (such as HoBr₃). Additional fills of this type are described further below.

0047<figref idref="DRAWINGS">FIG. 8</figref> shows an example RGBCYM wheel mechanical layout. As in the case of the RGBM wheel disclosed earlier, other layouts and ordering of the segments may be used in other embodiments.

0048Two examples are described below for color balancing the spectrum of <figref idref="DRAWINGS">FIG. 7</figref> to a color temperature of 11500K and 7000K, respectively. Both examples employ the methods of varying duty cycle and transmission spectra simultaneously. The transmission spectra of both designs differ only in the Magenta segment—the other segments' transmission spectra (and therefore their corresponding x/y coordinates) are the same. This is seen in <figref idref="DRAWINGS">FIG. 9</figref> and <figref idref="DRAWINGS">FIG. 10</figref>. Other embodiments may change the transmission spectra of other color segments as well.

0049<figref idref="DRAWINGS">FIG. 9A</figref> shows the example 11500K wheel spectra. This example shows how color balancing at a high CCT (greater than or equal to about 10000K) may be achieved. The 50%-crossing points on the Magenta segment are at M<b>1</b>=495 nm and M<b>2</b>=615 nm in this example. The corresponding X/Y plot is shown in <figref idref="DRAWINGS">FIG. 10</figref><i>a</i>, where it is seen that the system white point is well-balanced to the blackbody curve. The wheel duty cycles for this design are [T_R, T_G, T_B, T_C, T_Y, T_M]=[0.183 0.144 0.083 0.306 0.0720.211].

0050In other examples, an RGBCYM color wheel may be used to color balance at a CCT greater than or equal to 10000K. In these examples, the fill may be relatively balanced and include a metal halide that provides a relatively strong emission in or near the blue wavelengths and a metal halide that provides a relatively strong emission in or near the red wavelengths. In example embodiments, the 50% transmission points of a magenta color filter segment are, at the low end, in the range of about 485 nm to 510 nm or any range subsumed therein and, at the high end, in the range of about 580 nm to 625 nm or any range subsumed therein. In example embodiments, the duty cycle for red is in the range of about 0.15 to 0.2 or any range subsumed therein, the duty cycle for green is in the range of about 0.1 to 0.2 or any range subsumed therein, the duty cycle for blue is in the range of about 0.06 to 0.12 or any range subsumed therein, the duty cycle for cyan is in the range of about 0.25 to 0.35 or any range subsumed therein, the duty cycle for yellow is in the range of about 0.6 to 0.12 or any range subsumed therein and the duty cycle for magenta is in the range of about 0.15 to 0.25 or any range subsumed therein. These are examples only and other 50% transmission points and duty cycles may be used in other embodiments.

0051<figref idref="DRAWINGS">FIG. 9</figref><i>b </i>shows the example 7000K wheel spectra. The 50%-crossing points on the Magenta segment are at M<b>1</b>=495 nm and M<b>2</b>=580 nm. The corresponding X/Y plot is shown in <figref idref="DRAWINGS">FIG. 10B</figref>, where it is again seen that the system white point is well-balanced to the blackbody curve. As expected, the Magenta segment vertex at Mb is shifted with respect to the Magenta segment vertex Ma of the wheel design shown in <figref idref="DRAWINGS">FIG. 10A</figref>, causing the reduction in system white point color temperature. The wheel duty cycles for this design are [T_R, T_G, T_B, T_C, T_Y, T_M]=[0.231 0.144 0.164 0.200 0.072 0.189].

0052In other examples, an RGBCYM color wheel may be used to color balance at a CCT in the range of about 6000-10000K or any range subsumed therein. In these examples, the fill may be relatively balanced and include a metal halide that provides a relatively strong emission in or near the blue wavelengths and a metal halide that provides a relatively strong emission in or near the red wavelengths. In example embodiments, the 50% transmission points of a magenta color filter segment are, at the low end, in the range of about 470 nm to 510 nm or any range subsumed therein and, at the high end, in the range of about 550 nm to 610 nm or any range subsumed therein. In example embodiments, the duty cycle for red is in the range of about 0.15 to 0.3 or any range subsumed therein, the duty cycle for green is in the range of about 0.1 to 0.2 or any range subsumed therein, the duty cycle for blue is in the range of about 0.1 to 0.2 or any range subsumed therein, the duty cycle for cyan is in the range of about 0.15 to 0.3 or any range subsumed therein, the duty cycle for yellow is in the range of about 0.6 to 0.12 or any range subsumed therein and the duty cycle for magenta is in the range of about 0.15 to 0.25 or any range subsumed therein. These are examples only and other 50% transmission points and duty cycles may be used in other embodiments.

0053An example lamp and fills will now be described. Other embodiments may use other lamps and fills. In example embodiments, the fill may include metal halide, such as Indium Halide, Aluminum Halide and/or Holmium Halide. Some embodiments may also use Mercury and a noble gas in the fill. Other embodiments may be Mercury free.

0054In example embodiments, these fills are used in an electrodeless plasma lamp. <figref idref="DRAWINGS">FIG. 11</figref> is a cross-section and schematic view of an example electrodeless plasma lamp <b>100</b> that may be used in connection with an example embodiment. This is an example only and other plasma lamps may be used with other embodiments (see for example <figref idref="DRAWINGS">FIG. 12</figref>), including microwave or inductive plasma lamps. In the example of <figref idref="DRAWINGS">FIG. 11</figref>, the plasma lamp may have a lamp body <b>102</b> formed from one or more solid dielectric materials and a bulb <b>104</b> positioned adjacent to the lamp body <b>102</b>. The bulb <b>104</b> contains a fill that is capable of forming a light emitting plasma. A lamp drive circuit <b>106</b> couples radio frequency power into the lamp body <b>102</b> which, in turn, is coupled into the fill in the bulb <b>104</b> to form the light emitting plasma. In example embodiments, the lamp body <b>102</b> forms a waveguide that contains and guides the radio frequency power. In example embodiments, the radio frequency power may be provided at or near a frequency that resonates within the lamp body <b>102</b>. This is an example only and some embodiments may use a different electrodeless plasma lamp, such as a capacitively or inductively coupled plasma lamp, or other high intensity discharge lamp.

0055Lamp <b>100</b> has a drive probe <b>120</b> inserted into the lamp body <b>102</b> to provide radio frequency power to the lamp body <b>102</b>. In the example of <figref idref="DRAWINGS">FIG. 11</figref>, the lamp also has a feedback probe <b>122</b> inserted into the lamp body <b>102</b> to sample power from the lamp body <b>102</b> and provide it as feedback to the lamp drive circuit <b>106</b>. A lamp drive circuit <b>106</b> including a power supply, such as amplifier <b>124</b>, may be coupled to the drive probe <b>120</b> to provide the radio frequency power. The amplifier <b>124</b> may be coupled to the drive probe <b>120</b> through a matching network <b>126</b> to provide impedance matching. In an example embodiment, the lamp drive circuit <b>106</b> is matched to the load (formed by the lamp body, bulb and plasma) for the steady state operating conditions of the lamp. The lamp drive circuit <b>106</b> is matched to the load at the drive probe <b>120</b> using the matching network <b>126</b>.

0056In example embodiments, radio frequency power may be provided at a frequency in the range of between about 0.1 GHz and about 10 GHz or any range subsumed therein. The radio frequency power may be provided to drive probe <b>120</b> at or near a resonant frequency for lamp body <b>102</b>. The frequency may be selected based on the dimensions, shape and relative permittivity of the lamp body <b>102</b> to provide resonance in the lamp body <b>102</b>. In example embodiments, the frequency is selected for a fundamental resonant mode of the lamp body <b>102</b>, although higher order modes may also be used in some embodiments. In example embodiments, the RF power may be applied at a resonant frequency or in a range of from 0% to 10% above or below the resonant frequency or any range subsumed therein. In some embodiments, RF power may be applied in a range of from 0% to 5% above or below the resonant frequency. In some embodiments, power may be provided at one or more frequencies within the range of about 0 to 50 MHz above or below the resonant frequency or any range subsumed therein. In another example, the power may be provided at one or more frequencies within the resonant bandwidth for at least one resonant mode. The resonant bandwidth is the full frequency width at half maximum of power on either side of the resonant frequency (on a plot of frequency versus power for the resonant cavity).

0057In example embodiments, the radio frequency power causes a light emitting plasma discharge in the bulb. In example embodiments, power is provided by RF wave coupling. In example embodiments, RF power is coupled at a frequency that forms a standing wave in the lamp body (sometimes referred to as a sustained waveform discharge or microwave discharge when using microwave frequencies). In other example embodiments, a capacitively coupled or inductively coupled electrodeless plasma lamp may be used. Other high intensity discharge lamps may be used in other embodiments.

0058The bulb <b>104</b> may be quartz, sapphire, ceramic or other desired bulb material and may be cylindrical, pill shaped, spherical or other desired shape. In an example embodiment, the bulb is cylindrical in the center and forms a hemisphere at each end. In one example, the outer length (from tip to tip) is about 15 mm and the outer diameter (at the center) is about 5 mm. In this example, the interior of the bulb (which contains the fill) has an interior length of about 9 mm and an interior diameter at the center of about 2 mm. The wall thickness is about 1.5 mm along the sides of the cylindrical portion. The wall thickness at the front end is about 2.25 mm. In this example, the interior bulb volume is about 26.18 mm³. The wall thickness at the other end is about 3.75 mm. In other example embodiments, the bulb may have an interior width or diameter in a range between about 2 and 30 mm or any range subsumed therein, a wall thickness in a range between about 0.5 and 4 mm or any range subsumed therein, and an interior length between about 2 and 30 mm or any range subsumed therein. In example embodiments, the interior bulb volume may range from 10 mm³and 750 mm³or any range subsumed therein. These dimensions are examples only and other embodiments may use bulbs having different dimensions.

0059In example embodiments, the bulb <b>104</b> contains a fill that forms a light emitting plasma when radio frequency power is received from the lamp body <b>102</b>. The fill may include Aluminum Halide and/or Holmium Halide. In example embodiments, the dose amount of Aluminum Halide is in the range of from about from 1 to 50 micrograms per cubic millimeter of bulb volume, or any range subsumed therein. In example embodiments, the dose amount of Holium Halide is in the range of from about from 1 to 50 micrograms per cubic millimeter of bulb volume, or any range subsumed therein. In some embodiments, the dose of Aluminum Halide and the dose of Holmium Halide are each in the range of from about 10 to 10,000 micrograms or any range subsumed therein. In example embodiments, these dose amount result in a condensed pool of metal halide during lamp operation. A noble gas and additives such as Mercury may also be used. In example embodiments, the dose amount of Mercury is in the range of 10 to 100 micrograms of Mercury per mm³of bulb volume, or any range subsumed therein. In some embodiments, the dose of Mercury may be in the range of from about 0.5 to 5 milligrams or any range subsumed therein. An ignition enhancer may also be used. A small amount of an inert radioactive emitter such as Kr85 may be used for this purpose. In some examples, Kr85 may be provided in the range of about 5 nanoCurie to 1 microCurie or any range subsumed therein.

0060In a particular example embodiment, the fill includes Aluminum Iodide or Aluminum Bromide in the range from about 0.05 mg to 0.3 mg or any range subsumed therein, and Holmium Iodide or Holmium Bromide in the range from about 0.05 mg to 0.3 mg or any range subsumed therein. Aluminum Chlorides and Holmium Chlorides may also be used in some embodiments. In some embodiments, Aluminum Halide and Holmium Halide are provided in equal amounts. In other embodiments, the ratio of Aluminum Halide to Holmium Halide may be 10:90, 20:80, 30:70, 40:60, 60:40, 70:30, 80:20 or 90:10. Other metal halides may also be used in other embodiments in addition to Aluminum Halide and/or Holmium Halide, including Bromides, Iodides and Chlorides of Indium, Aluminum, Gallium, Thalium, Holmium, Dysprosium, Cerium, Cesium, Erbium, Thulium, Lutetium and Gadolinium. Other metal halides may also be used in other embodiments, including Bromides, Iodides and Chlorides of Sodium, Calcium, Strontium, Yttrium, Tin, Antimony, Thorium and any of the elements in the Lanthanide series.

0061Some embodiments may use a combination of metal halides to produce a desired spectrum. In some examples, one or more metal halides with strong emission in the blue color range (such as halides of Aluminum, Cesium, Gallium, Indium and/or Scandium) may be combined with one or more metal halides to enhance emission in the red color range (such as halides of Sodium, Calcium, Strontium, Gadolinium, Dysprosium, Holmium, Erbium and/or Thulium). In particular example embodiments, the fill may include (1) Aluminum Halide and Holmium Halide; (2) Aluminum Halide and Erbium Halide; (3) Gallium Halide and Holmium Halide; (4) Gallium Halide and Erbium Halide; (5) any of these fill further including Indium Halide; (6) any of these fills further including an alkali metal halide such as Sodium Halide or Cesium Halide (although other examples may specifically exclude all alkali metals); and (7) any of these fills further including Cerium Halide.

0062In some example embodiments, the example fills described in the preceding paragraph may be used in a projection display system with an RGBCYM color wheel of the type described above. In example embodiments, the color wheel uses 50% transmission points for magenta and duty cycles within any of the ranges described above to color balance at a CCT in the range of about 6000 to 11500 K or any range subsumed therein.

0063In other example embodiments, any of the above fills that are strong in the blue or green ranges (including halides of Aluminum, Cesium, Gallium, Indium and/or Scandium) or other fills may be used in a projection display system with an RGBM color wheel of the type described above. In example embodiments, the color wheel uses 50% transmission points for magenta and duty cycles within any of the ranges described above to color balance at a CCT in the range of about 6000 to 11500 K or any range subsumed therein.

0064Example metal halide and Mercury fills include, but are not limited to, the fills described in Table 1 below.

0000<tables id="TABLE-US-00001" num="00001"><table frame="none" colsep="0" rowsep="0" pgwide="1"><tgroup align="left" colsep="0" rowsep="0" cols="10"><colspec colname="1" colwidth="14pt" align="center" /><colspec colname="2" colwidth="28pt" align="center" /><colspec colname="3" colwidth="28pt" align="center" /><colspec colname="4" colwidth="28pt" align="center" /><colspec colname="5" colwidth="28pt" align="center" /><colspec colname="6" colwidth="28pt" align="center" /><colspec colname="7" colwidth="28pt" align="center" /><colspec colname="8" colwidth="28pt" align="center" /><colspec colname="9" colwidth="28pt" align="center" /><colspec colname="10" colwidth="35pt" align="center" /><thead><row><entry namest="1" nameend="10" rowsep="1">TABLE 1</entry></row><row><entry namest="1" nameend="10" align="center" rowsep="1" /></row><row><entry>Fill</entry><entry>InBr</entry><entry>DyI₃</entry><entry>CeI₃</entry><entry>HoBr₃</entry><entry>AlBr₃</entry><entry>ErBr₃</entry><entry>GdI₃</entry><entry>HoI₃</entry><entry>Hg</entry></row><row><entry namest="1" nameend="10" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry>#1</entry><entry>0.1 mg</entry><entry>0.1 mg</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>2.7 mg</entry></row><row><entry>#2</entry><entry>0.1 mg</entry><entry>0</entry><entry>0.1 mg</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>2.7 mg</entry></row><row><entry>#3</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0.05 mg</entry><entry>0.05 mg</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>1.35 mg </entry></row><row><entry>#4</entry><entry>0.1 mg</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry> 0.1 mg</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>2.7 mg</entry></row><row><entry>#5</entry><entry>0.1 mg</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0.1 mg</entry><entry>0</entry><entry>2.7 mg</entry></row><row><entry>#6</entry><entry>0.1 mg</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0.1 mg</entry><entry>2.7 mg</entry></row><row><entry>#7</entry><entry>0.1 mg</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>1.6 mg</entry></row><row><entry>#8</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0</entry><entry>0.05 mg</entry><entry>0.05 mg</entry><entry>0</entry><entry>0</entry><entry>1.35 mg </entry></row><row><entry namest="1" nameend="10" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0065In an example embodiment, the metal halide(s) may be provided in the range from about 0.01 mg to 10 mg or any range subsumed therein and Mercury may be provided in the range of about 0.01 to 10 mg or any range subsumed therein. In example embodiments, the fill includes 1 to 100 micrograms of metal halide per mm³of bulb volume, or any range subsumed therein, 1 to 100 micrograms of Mercury per mm³of bulb volume, or any range subsumed therein, and 5 nanoCurie to 1 microCurie of a radioactive ignition enhancer, or any range subsumed therein. In other examples, the fill may include a dose of one or more metal halides in the range of about 1 to 100 micrograms of metal halide per mm³of bulb volume without Mercury. In some embodiments using more than one metal halide, the total dose may be in any of the above ranges and the percentage of each metal halide may range from 5% to 95% of the total dose. In example embodiments, fills including any of the above metal halides may be used in a projection display system with an RGBM color wheel of the type described above or an RGBCYM color wheel of the type described above.

0066In example embodiments, a high pressure fill is used to increase the resistance of the gas. This can be used to decrease the overall startup time required to reach full brightness for steady state operation. In one example, a noble gas such as Helium, Neon, Argon, Krypton or Xenon, or another substantially non-reactive gas such as Nitrogen, or a combination of these gases is provided at high pressures between 200 Torr to 3000 Torr or any range subsumed therein. Pressures less than or equal to 760 Torr may be desired in some embodiments to facilitate filling the bulb at or below atmospheric pressure. In particular embodiments, pressures between 400 Torr and 600 Torr are used to enhance starting. Example high pressure fills may also include Aluminum Halide, Holmium Halide and Mercury which have a relatively low vapor pressure at room temperature. An ignition enhancer such as Kr85 may also be used. The above pressures are measured at 22° C. (room temperature). It is understood that much higher pressures are achieved at operating temperatures after the plasma is formed. For example, the lamp may provide a high intensity discharge at high pressure during operation (e.g., greater than 2 atmospheres and 10-30 atmospheres or more in example embodiments or any range subsumed therein).

0067In example embodiments, the bulb is provided with a fill including Aluminum Halide, Holmium Halide and Mercury in amounts selected to provide 15,000 to 20,000 lumens (or any range subsumed therein) at a correlated color temperature of 4000 to 10000 K (or any range subsumed therein) with a bulb geometry enabling the collection of 4500 to 5500 lumens (or any range subsumed therein) in 27 mm²steradian when operated at 150 to 200 watts (or any range subsumed therein). In some embodiments, the fill may be selected to provide a correlated color temperature in the range of 6000 to 9000 K. These doses, pressures and fills are examples only and other doses, pressures and fills may be used in other embodiments.

0068The lamp of <figref idref="DRAWINGS">FIG. 11</figref> will now be described in further detail. As shown in <figref idref="DRAWINGS">FIG. 11</figref>, the amplifier <b>124</b> may be coupled to the drive probe <b>120</b> through a matching network <b>126</b> to provide impedance matching. In an example embodiment, the amplifier <b>124</b> is matched to about 50 ohms for the steady state operating conditions of the lamp.

0069In example embodiments, the amplifier <b>124</b> may be operated in multiple operating modes at different bias conditions to improve starting and then to improve overall amplifier efficiency during steady state operation. For example, the amplifier may be biased to operate in Class A/B mode to provide better dynamic range during startup and in Class C mode during steady state operation to provide more efficiency. The amplifier may also have a gain control that can be used to adjust the gain of the amplifier <b>124</b>. Amplifier <b>124</b> may include either a plurality of gain stages or a single stage.

0070The feedback probe <b>122</b> is coupled to the input of the amplifier <b>124</b> through an attenuator <b>128</b> and phase shifter <b>130</b>. The attenuator <b>128</b> is used to adjust the power of the feedback signal to an appropriate level for input to the phase shifter <b>130</b>. In some embodiments, a second attenuator may be used between the phase shifter <b>130</b> and the amplifier <b>124</b> to adjust the power of the signal to an appropriate level for amplification by the amplifier <b>124</b>. In some embodiments, the attenuator(s) may be variable attenuators controlled by the control electronics <b>132</b>. In other embodiments, the attenuators may be set to a fixed value. In some embodiments, the lamp drive circuit may not include an attenuator. In an example embodiment, the phase shifter <b>130</b> may be a voltage-controlled phase shifter controlled by the control electronics <b>132</b>.

0071The feedback loop automatically oscillates at a frequency based on the load conditions and phase of the feedback signal. This feedback loop may be used to maintain a resonant condition in the lamp body <b>102</b> even though the load conditions change as the plasma is ignited and the temperature of the lamp changes. If the phase is such that constructive interference occurs for waves of a particular frequency circulating through the loop, and if the total response of the loop (including the amplifier, lamp, and all connecting elements) at that frequency is such that the wave is amplified rather than attenuated after traversing the loop, the loop will oscillate at that frequency. Whether a particular setting of the phase-shifter induces constructive or destructive feedback depends on frequency. The phase-shifter <b>128</b> can be used to finely tune the frequency of oscillation within the range supported by the lamp's frequency response. In doing so, it also effectively tunes how well RF power is coupled into the lamp because power absorption is frequency-dependent. Thus, the phase-shifter <b>128</b> provides fast, finely-tunable control of the lamp output intensity. Both tuning and detuning are useful. For example: tuning can be used to maximize intensity as component aging changes the overall loop phase; detuning can be used to control lamp dimming. In some example embodiments, the phase selected for steady state operation may be slightly out of resonance, so maximum brightness is not achieved. This may be used to leave room for the brightness to be increased and/or decreased by control electronics <b>130</b>.

0072In <figref idref="DRAWINGS">FIG. 11</figref>, control electronics <b>132</b> is connected to attenuator <b>128</b>, phase shifter <b>130</b> and amplifier <b>124</b>. The control electronics <b>132</b> may also be connected to line <b>76</b> (shown in <figref idref="DRAWINGS">FIG. 1A</figref>) to receive input from the system control electronics <b>70</b> (shown in <figref idref="DRAWINGS">FIG. 1A</figref>). The control electronics <b>132</b> provide signals to adjust the level of attenuation provided by the attenuator <b>128</b>, phase of phase shifter <b>130</b>, the class in which the amplifier <b>124</b> operates (e.g., Class A/B, Class B or Class C mode) and/or the gain of the amplifier <b>124</b> to control the power provided to the lamp body <b>102</b>. In one example, the amplifier <b>124</b> has three stages, a pre-driver stage, a driver stage and an output stage, and the control electronics <b>132</b> provides a separate signal to each stage (drain voltage for the pre-driver stage and gate bias voltage of the driver stage and the output stage). The drain voltage of the pre-driver stage can be adjusted to adjust the gain of the amplifier. The gate bias of the driver stage can be used to turn on or turn off the amplifier. The gate bias of the output stage can be used to chose the operating mode of the amplifier (e.g., Class A/B, Class B or Class C). Control electronics <b>130</b> can range from a simple analog feedback circuit to a microprocessor/microcontroller with embedded software or firmware that controls the operation of the lamp drive circuit. The control electronics <b>130</b> may include a lookup table or other memory that contains control parameters (e.g., amount of phase shift or amplifier gain) to be used when certain operating conditions are detected. In example embodiments, feedback information regarding the lamp's light output intensity is provided either directly by an optical sensor <b>134</b>, e.g., a silicon photodiode sensitive in the visible wavelengths, or indirectly by an RF power sensor <b>136</b>, e.g., a rectifier. The RF power sensor <b>136</b> may be used to determine forward power, reflected power or net power at the drive probe <b>120</b> to determine the operating status of the lamp. A directional coupler may be used to tap a small portion of the power and feed it to the RF power sensor <b>136</b>. An RF power sensor may also be coupled to the lamp drive circuit at the feedback probe <b>122</b> to detect transmitted power for this purpose. In some embodiments, the control electronics <b>132</b> may adjust the phase shifter <b>130</b> on an ongoing basis to automatically maintain desired operating conditions.

0073The phase of the phase shifter <b>130</b> and/or gain of the amplifier <b>124</b> may also be adjusted after startup to change the operating conditions of the lamp. For example, the power input to the plasma in the bulb <b>104</b> may be modulated to modulate the intensity of light emitted by the plasma. This can be used for brightness adjustment or to modulate the light to adjust for video effects in a projection display. For example, a projection display system may use a microdisplay that controls intensity of the projected image using pulse-width modulation (PWM). PWM achieves proportional modulation of the intensity of any particular pixel by controlling, for each displayed frame, the fraction of time spent in either the “ON” or “OFF” state. By reducing the brightness of the lamp during dark frames of video, a larger range of PWM values may be used to distinguish shades within the frame of video. The brightness of the lamp may also be modulated during particular color segments of a color wheel for color balancing or to compensate for green snow effect in dark scenes by reducing the brightness of the lamp during the green segment of the color wheel. The system control electronics <b>70</b> (shown in <figref idref="DRAWINGS">FIG. 1A</figref>) may provide signals via line <b>76</b> (shown in <figref idref="DRAWINGS">FIG. 1A</figref>) to control the operating mode and brightness of the lamp in example embodiments.

0074In another example, the phase shifter <b>130</b> can be modulated to spread the power provided by the lamp circuit <b>106</b> over a larger bandwidth. This can reduce ElectroMagnetic Interference (EMI) at any one frequency and thereby help with compliance with FCC regulations regarding EMI. In example embodiments, the degree of spectral spreading may be from 5-30% or any range subsumed therein. In one example, the control electronics <b>132</b> may include circuitry to generate a sawtooth voltage signal and sum it with the control voltage signal to be applied to the phase shifter <b>130</b>. In another example, the control electronics <b>132</b> may include a microcontroller that generates a Pulse Width Modulated (PWM) signal that is passed through an external low-pass filter to generate a modulated control voltage signal to be applied to the phase shifter <b>130</b>. In example embodiments, the modulation of the phase shifter <b>130</b> can be provided at a level that is effective in reducing EMI without any significant impact on the plasma in the bulb.

0075Additional aspects of electrodeless plasma lamps according to example embodiments will now be described with reference to <figref idref="DRAWINGS">FIG. 11</figref>. In example embodiments, the lamp body <b>102</b> has a relative permittivity greater than air. The frequency required to excite a particular resonant mode in the lamp body <b>102</b> generally scales inversely to the square root of the relative permittivity (also referred to as the dielectric constant) of the lamp body. As a result, a higher relative permittivity results in a smaller lamp body required for a particular resonant mode at a given frequency of power. The shape and dimensions of the lamp body <b>102</b> also affect the resonant frequency as described further below. In an example embodiment, the lamp body <b>102</b> is formed from solid alumina having a relative permittivity of about 9.2. In some embodiments, the dielectric material may have a relative permittivity in the range of from 2 to 100 or any range subsumed therein, or an even higher relative permittivity. In some embodiments, the body may include more than one such dielectric material resulting in an effective relative permittivity for the body within any of the ranges described above. The body may be rectangular, cylindrical or other shape as described further below.

0076In example embodiments, the outer surfaces of the lamp body <b>102</b> may be coated with an electrically conductive coating <b>108</b>, such as electroplating or a silver paint or other metallic paint which may be fired onto the outer surface of the lamp body. The electrically conductive material <b>108</b> may be grounded to form a boundary condition for the radio frequency power applied to the lamp body <b>102</b>. The electrically conductive coating helps contain the radio frequency power in the lamp body. Regions of the lamp body may remain uncoated to allow power to be transferred to or from the lamp body. For example, the bulb <b>104</b> may be positioned adjacent to an uncoated portion of the lamp body to receive radio frequency power from the lamp body.

0077In the example embodiment of <figref idref="DRAWINGS">FIG. 11</figref>, an opening <b>110</b> extends through a thin region <b>112</b> of the lamp body <b>102</b>. The surfaces <b>114</b> of the lamp body <b>102</b> in the opening <b>110</b> are uncoated and at least a portion of the bulb <b>104</b> may be positioned in the opening <b>110</b> to receive power from the lamp body <b>102</b>. In example embodiments, the thickness H<b>2</b> of the thin region <b>112</b> may range from 1 mm to 10 mm or any range subsumed therein and may be less than the outside length and/or interior length of the bulb. One or both ends of the bulb <b>104</b> may protrude from the opening <b>110</b> and extend beyond the electrically conductive coating <b>108</b> on the outer surface of the lamp body. This helps avoid damage to the ends of the bulbs from the high intensity plasma formed adjacent to the region where power is coupled from the lamp body. In other embodiments, all or a portion of the bulb may be positioned in a cavity extending from an opening on the outer surface of the lamp body and terminating in the lamp body. In other embodiments, the bulb may be positioned adjacent to an uncoated outer surface of the lamp body or in a shallow recess formed on the outer surface of the waveguide body. In some example embodiments, the bulb may be positioned at or near an electric field maxima for the resonant mode excited in the lamp body.

0078A layer of material <b>116</b> may be placed between the bulb <b>104</b> and the dielectric material of lamp body <b>102</b>. In example embodiments, the layer of material <b>116</b> may have a lower thermal conductivity than the lamp body <b>102</b> and may be used to optimize thermal conductivity between the bulb <b>104</b> and the lamp body <b>102</b>. In an example embodiment, the layer <b>116</b> may have a thermal conductivity in the range of about 0.5 to 10 watts/meter-Kelvin (W/mK) or any range subsumed therein. For example, alumina powder with 55% packing density (45% fractional porosity) and thermal conductivity in a range of about 1 to 2 watts/meter-Kelvin (W/mK) may be used. In some embodiments, a centrifuge may be used to pack the alumina powder with high density. In an example embodiment, a layer of alumina powder is used with a thickness D<b>5</b> within the range of about ⅛ mm to 1 mm or any range subsumed therein. Alternatively, a thin layer of a ceramic-based adhesive or an admixture of such adhesives may be used. Depending on the formulation, a wide range of thermal conductivities is available. In practice, once a layer composition is selected having a thermal conductivity close to the desired value, fine-tuning may be accomplished by altering the layer thickness. Some example embodiments may not include a separate layer of material around the bulb and may provide a direct conductive path to the lamp body. Alternatively, the bulb may be separated from the lamp body by an air-gap (or other gas filled gap) or vacuum gap.

0079In some example embodiments, alumina powder or other material may also be packed into a recess <b>118</b> formed below the bulb <b>104</b>. In the example shown in <figref idref="DRAWINGS">FIG. 11</figref>, the alumina powder in the recess <b>118</b> is outside the boundaries of the waveguide formed by the electrically conductive material <b>108</b> on the surfaces of the lamp body <b>102</b>. The material in the recess <b>118</b> provides structural support, reflects light from the bulb and provides thermal conduction. One or more heat sinks may also be used around the sides and/or along the bottom surface of the lamp body to manage temperature. Thermal modeling may be used to help select a lamp configuration providing a high peak plasma temperature resulting in high brightness, while remaining below the working temperature of the bulb material. Example thermal modeling software includes the TAS software package available commercially from Harvard Thermal, Inc. of Harvard, Mass.

0080<figref idref="DRAWINGS">FIG. 12</figref> is a cross-section and schematic view of a plasma lamp <b>200</b> that may be used as a light source in a projection system according to an example embodiment. It should be noted that the fills/color wheels and methodology described above are capable of use in combination with the plasma lamp <b>200</b>. As in the case of the lamp <b>100</b>, the plasma lamp <b>200</b> may have a lamp body <b>202</b> formed from one or more solid dielectric materials and a bulb <b>204</b> positioned adjacent to the lamp body <b>202</b>. As described above, the bulb <b>204</b> contains a fill that is capable of forming a light emitting plasma. A lamp drive circuit <b>206</b> couples radio frequency (RF) power into the lamp body <b>202</b> which, in turn, is coupled into the fill in the bulb <b>204</b> to form the light emitting plasma. In example embodiments, the lamp body <b>202</b> forms a structure that contains and guides the radio frequency power.

0081Unlike the plasma lamp <b>100</b>, in the plasma lamp <b>200</b> the bulb <b>204</b> is positioned or orientated so that a length of a plasma arc <b>208</b> generally faces a lamp opening <b>210</b> (as opposed to facing side walls <b>220</b>) to increase an amount of collectable light emitted from the plasma arc in a given etendue. Since the length of plasma arc orients in a direction of an applied electric field, the lamp body <b>202</b> and the coupled RF power are configured to provide an electric field <b>214</b> that is aligned or substantially parallel to the length of the bulb <b>204</b> and a front or upper surface <b>216</b> of the lamp body <b>202</b>. Thus, in an example embodiment, the length of the plasma arc <b>204</b> may be substantially (if not completely) visible from outside the lamp body <b>202</b>. In example embodiments, collection optics (see for example <figref idref="DRAWINGS">FIG. 1A</figref>) may be in the line of sight of the full length of the bulb <b>204</b> and plasma arc <b>208</b>. In other examples, about 40%-100%, or any range subsumed therein, of the plasma arc may be visible to the collection optics (see <figref idref="DRAWINGS">FIG. 1A</figref>) in front of the lamp <b>200</b>. Accordingly, the amount of light emitted from the bulb <b>204</b> and received by the collection optics may be enhanced. In example embodiments, a substantial amount of light may be emitted out of the lamp <b>200</b> from the plasma arc through the opening <b>210</b> in the front side wall of the lamp <b>200</b> without any internal reflection. The lamp body <b>202</b> may be configured to realize the necessary resonator structure such that the light emission of the lamp <b>200</b> is enabled while satisfying Maxwell's equations.

0082The lamp body <b>202</b> may include a solid dielectric body and an electrically conductive coating which extends to the front or upper surface <b>216</b>. The lamp <b>200</b> is also shown to include dipole arms <b>222</b> and conductive elements <b>224</b>, <b>226</b> (e.g., metallized cylindrical holes bored into the body <b>202</b>) to concentrate the electric field present in the lamp body <b>202</b>. The dipole arms <b>222</b> may thus define an internal dipole. In an example embodiment, a resonant frequency applied to a lamp body <b>202</b> without dipole arms <b>222</b> and conductive elements <b>224</b>, <b>226</b> would result in a high electric field at the center of the solid dielectric lamp body <b>202</b>. This is based on the intrinsic resonant frequency response of the lamp body due to its shape, dimensions and relative permittivity. However, in the example embodiment of the lamp <b>200</b> shown in <figref idref="DRAWINGS">FIG. 12</figref>, the shape of the standing waveform inside the lamp body <b>202</b> is substantially modified by the presence of the dipole arms <b>222</b> and conductive elements <b>224</b>, <b>226</b> and the electric field maxima is brought out to end portions <b>228</b>, <b>230</b> of the bulb <b>204</b> using the internal dipole structure. This results in the electric field <b>214</b> near the upper surface <b>216</b> of the lamp <b>200</b> that is substantially parallel to the length of the bulb <b>204</b>. In some example embodiments, this electric field is also substantially parallel to a drive probe <b>240</b> and a feedback probe <b>242</b>.

0083The plasma lamp <b>200</b> may include an example lamp drive circuit <b>206</b>. The circuit <b>206</b> is connected to the drive probe <b>240</b> inserted into the lamp body <b>202</b> to provide radio frequency power to the lamp body <b>202</b>. In the example embodiment, the lamp <b>200</b> is also shown to include the feedback probe <b>242</b> inserted into the lamp body <b>202</b> to sample power from the lamp body <b>202</b> and provide it as feedback to the lamp drive circuit <b>206</b>.

0084Various positions for the probes <b>240</b>, <b>242</b> are possible. The physical principle governing their position is the degree of desired power coupling versus the strength of the E-field in the lamp body <b>202</b>. For the drive probe <b>240</b>, the desire is for strong power coupling. Therefore, the drive probe <b>240</b> may be located near a field maximum in some embodiments. For the feedback probe <b>242</b>, the desire is for weak power coupling. Therefore, the feedback probe <b>242</b> may be located away from a field maximum in some embodiments.

0085The lamp drive circuit <b>206</b> is shown to include a power supply, such as amplifier <b>254</b>, which may be coupled to the drive probe <b>240</b> to provide the radio frequency power. The amplifier <b>254</b> may be coupled to the drive probe <b>240</b> through a directional coupler <b>256</b> to provide impedance matching. The directional coupler <b>256</b> may be connected to control electronics <b>260</b> via an RF power sensor <b>258</b>. In an example embodiment, the lamp drive circuit <b>206</b> is matched to the load (formed by the lamp body <b>202</b>, the bulb <b>204</b> and the plasma) for the steady state operating conditions of the lamp <b>200</b>.

0086The feedback probe <b>242</b> is shown to be coupled to an input of the amplifier <b>254</b> (which may resemble the amplifier <b>124</b>) through an attenuator <b>250</b> and the phase shifter <b>252</b>. The attenuator <b>250</b> is used to adjust the power of the feedback signal to an appropriate level for input to the phase shifter <b>252</b>. In some example embodiments, a second attenuator may be used between the phase shifter <b>252</b> and the amplifier <b>254</b> to adjust the power of the signal to an appropriate level for amplification by the amplifier <b>254</b>. In some embodiments, the attenuator(s) may be variable attenuators controlled by control electronics <b>260</b>. In other embodiments, the attenuator(s) may be set to a fixed value. In some embodiments, the lamp drive circuit <b>206</b> may not include an attenuator. In an example embodiment, the phase shifter <b>252</b> may be a voltage-controlled phase shifter controlled by the control electronics <b>260</b>. In example embodiments, feedback information regarding the lamp's light output intensity is provided either directly by the optical sensor <b>221</b>, e.g., a silicon photodiode sensitive in the visible wavelengths, or indirectly by the RF power sensor, e.g., a rectifier.

0087In an example embodiment, the control electronics <b>260</b> may resemble the control electronics <b>132</b> and may also be connected to line <b>76</b> (shown in <figref idref="DRAWINGS">FIG. 1A</figref>) to receive input from the system control electronics <b>70</b> (shown in <figref idref="DRAWINGS">FIG. 1A</figref>). The control electronics <b>260</b> may provide signals to adjust the level of attenuation provided by the attenuator <b>250</b>, phase of phase shifter <b>252</b>, the class in which the amplifier <b>254</b> operates (e.g., Class A/B, Class B or Class C mode) and/or the gain of the amplifier <b>254</b> to control the power provided to the lamp body <b>202</b>.

0088The above circuits, dimensions, shapes, materials and operating parameters are examples only and other embodiments may use different circuits, dimensions, shapes, materials and operating parameters.