Lamp based on LEDs' light emission

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DESCRIPTION

Luminaire based on the light emission of light-emitting diodes.

The present invention refers to a luminaire that includes a housing that defines an internal space that contains at least one light source constituted by an electroluminescent diode (LED) and optical means for guiding the light emitted by the LED to the outside of the housing, said optical means being suitable for concentrating the light emitted by the LED into a beam.

Such a luminaire is known from WO 98/33007. This luminaire, designed for street lighting, takes advantage of the light emitted by LED: the optical guiding means used guarantee, on the one hand, the concentration of the intensity produced by LED in a beam and, on the other hand, the directing of the make.

The emission characteristic of a LED has a particular shape. The optical media, which put into practice the principles of physical optics, have a geometry that allows optimal performances for a precise and constant position of the optical media with respect to the emission characteristic of the LED. As the luminaire is intended to be transported and later installed, the robustness of the mounting of the optical media with respect to the LED support must be guaranteed so that the luminaires retain the properties announced by the manufacturer.

In WO 98/33007, the LED is fixed to the interior of the optical means which in turn are fixed to the housing. Carrying out this setup requires delicate manipulations of the LED. However, LED's are very sensitive to mechanical manipulations: their useful life and their luminous performance depend on the care taken in handling them, especially during their assembly inside a luminaire according to the introductory paragraph. The LED presents, among other things, a fragile dome on which no significant stresses should be exerted. Therefore delicate assembly, such as that proposed by WO 98/33007, should be avoided. Furthermore, this assembly is time consuming and expensive in automated operations.

Document EP 0 596 782 A discloses a luminaire according to the preamble of claim 1.

An object of the invention is to largely solve the problem of mounting the optical means with respect to the LED, inside the luminaire.

A luminaire according to the introductory paragraph is notable according to the invention in that the LED is mounted on a bracket connected to the housing and because the optical means are clamped between a clamping element connected to the housing and the LED bracket.

The assembly thus carried out consists of placing the optical means on the LED support and using a fastening element connected to the housing to fasten them. This assembly has the advantage of not requiring delicate manipulations of the LED that can be pre-installed on its support, of being fast and of being easily automated.

In an embodiment of the invention, the optical means are elastically clamped between the clamping element connected to the housing and the LED holder by elastic clamping means. Said elastic clamping means then exert pressure on the optical means with the help of the clamping element connected to the housing. Consequently, the optical media exerts pressure on the LED support. Therefore, the mechanical clearances that can exist between the clamping element connected to the housing and the optical means and between the optical means and the LED support are corrected and this prevents the relative movements of the optical means with respect to the LED support. . Advantageously, the shapes of the optical means and that of the LED support are adapted in such a way that, under pressure, the contact between the optical means and the LED support participates to guarantee a precise and constant position, providing optimum performance to the whole. In a preferred implementation of the invention, the elastic fastening means of the optical means are made by means of a block of elastic material positioned so that it is compressed between the fastening element connected to the housing and the optical means. Said elastic material can especially belong to all types of foams. This solution has the advantage of being simple to implement and of allowing the intensity of the pressure exerted by the optical means on the LED support to be controlled by choosing the characteristics of the elastic material used.

In an advantageous implementation of the invention, a low coefficient of adhesion material is placed between the optical means and the fastener connected to the housing. This material makes the contact between the optical media and either the optical media holding element or the elastic holding means. The effect of this material with a low coefficient of adhesion, which can be polyethylene, is to facilitate relative translational movements at the level of contact between the optical means and either the fastening element connected to the housing, or the means elastic support. Translational movements of the fastening element connected to the casing or of the elastic fastening means, with respect to the casing on which the LED support is fixed, can in fact drag the optical means which, in that case, move of its position of optimal returns with respect to the emission characteristic of the LED. These translational movements, which result in slipping at the level of the contacts between objects, may be the result of external mechanical stress such as differences in thermal expansion between different materials. Indeed, in this environment in which objects made of different materials are found and in which the temperature experiences great variations, the differences in expansion are sources of relative movements between said objects, movements that may not be negligible.

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In an advantageous embodiment of the invention, the clamping element connected to the casing is connected to the casing by means of gluing means. This solution makes it possible to avoid the use of screws.

Screws are commonly used in the field of luminaires but present problems from the point of view of the differences in expansion when the fixed materials are different, which is generally the case for a luminaire according to the introductory paragraph. A complementary advantage is that of allowing a more important miniaturization of the luminaire than with screws, because the use of gluing means requires a certain surface but does not occupy more important material space.

In a particular embodiment of the invention, the gluing means are adhesive strips.

In a particularly advantageous embodiment of the invention, the fastening element connected to the housing is a plate that transmits light. This arrangement is advantageously adopted when the plate that transmits the light is superimposed on the optical means since, in that case, it fulfills two functions: to protect the generally fragile optical means, and to hold said optical means.

The invention will be better understood in the light of the following description of some embodiments, made by way of example and with respect to the accompanying drawings, in which:

- figure 1 is a section representing an example of a luminaire according to the invention,

Figure 2 is an exploded perspective view of another example of a luminaire that puts the invention into practice,

figure 3 is a partial view from above of an improved embodiment of the luminaire of figure 2,

Figure 4 is a perspective view of a piece for adjusting mechanical clearances put into practice in a particular embodiment of the invention of the type of Figures 2 and 3.

Figure 1 shows a section of a luminaire according to an advantageous embodiment of the invention. This figure is only indicative of one embodiment.

This luminaire includes a housing 1 containing a light source constituted by an electroluminescent diode 2 (LED) mounted on a support 3 fixed to housing 1. Support 3 of the LED is a printed circuit and the fixing of said support 3 to the casing 1 is made by gluing means. The use of gluing means, for example an adhesive strip, has the advantage of participating in a correct evacuation of the heat. Indeed, the bonding means have good thermal conduction properties and allow a maximum contact surface between the support 3 and the housing 1. In the embodiment described here, the support 3 is flat, but this does not exclude other geometries of the bracket 3.

The optical means here comprise a collimator 4 made up by mass of a material that transmits light and resistant to temperature, for example poly (methyl methacrylate) (PMMA). The optical means are in this case a "solid" collimator 4 but they can also be constituted, for example, by a conical hollow reflector. The collimator 4 has a lateral surface 5 with symmetry of revolution with a parabolic or conical base, a frontal surface 6 in this case flat and a surface that forms a base 7, geometrically opposite to the frontal surface 6. In this case the base 7 is flat but this characteristic does not exclude other geometries. The lateral surface 5 of the collimator 4 allows the light emitted by the LED 2 to be concentrated in a beam. In this case, the beam obtained is a directing beam of light made up of parallel rays. This light beam leaves the collimator 4 through the front surface 6 and the direction of said beam is perpendicular to the plane defined by this front surface 6. The emission characteristic of the system comprising the DEL 2 and the collimator 4 therefore has a maximum emission direction that is, in this example, perpendicular to the plane defined by the front surface 6 of the collimator 4.

The collimator 4 also has, at its base 7, a cavity 8 designed to house the LED 2. The collimator 4 is positioned above the LED 2. As the LED is sensitive to the pressures that can be exerted on its dome 9, the Contacts that may exist between the DEL 2 and the collimator 4 are minimized by oversizing the dimensions of the cavity 8 and the collimator 4 rests by its base 7 on the support 3 on which the DEL 2 is mounted.

The optimal luminous performances of the collimator 4, that is, the control of the structure of the beam and its power, are obtained for a precise position of the collimator 4 with respect to the emission characteristic of the LED 2. In this case, a lateral displacement By translation of the base 7 of the collimator 4 with respect to the LED 2 of more than 4% of the diameter of the LED, this leads to a loss of efficiency of more than 10%. The clearances on the dimensions of the base 7 of the collimator 4 as well as on the dimensions of the cavity 8 are calculated in this case so that the lateral translations of the collimator 4 with respect to the DEL 2 are of sufficiently small amplitude to guarantee good luminous performances. at the output of the collimator 4. These dimensions also take into account the need not to impose significant lateral stresses on the LED 2.

Placing the collimator 4 on the support 3 of the LED 2 allows, by means of the dimensions made on the different elements, to guarantee a first placement that will be held by the clamping element connected to the housing

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1. This holding element is, in this embodiment, a plate 10 that transmits light: therefore the plate 10 that transmits light is superimposed on the collimator 4, compressing a block 11 of elastic material. The plate 10 is connected to the housing 1 by a double-sided adhesive strip 12. Therefore, the collimator 4, a fragile optical instrument, is therefore protected by the plate 10 that transmits the light from external aggressions that can damage it and impair its optical performance. The use of gluing means, such as the adhesive strip 12, also has the advantage of participating in the sealing of the luminaire. Taking into account that the housing 1 and the plate 10 are made in principle with different materials and therefore are subjected to differences in expansion, the use of gluing means, such as an adhesive strip 12, whose properties of resistance to shear can be chosen judiciously, it is also a solution to allow the relative movements of the casing 1 and of the plate 10.

In this example, the block 11 of elastic material is fixed on the front surface 6 of the collimator 4. The elastic material can be chosen from all types of foam, of different densities and of different shapes depending on the intensity of the pressure being applied. you want to exert on the collimator 4 to keep it in place. In an embodiment, the block 11 of elastic material consisted of a single-sided adhesive foam of vinyl weighing 225 kg / m³ density, 6 mm thick and 3 mm wide. Numerous variants of the invention are possible with regard to the elastic fastening of the optical means as well as the positioning of the elastic fastening means with respect to the other elements of the luminaire: for example, the implementation of springs can be considered; Placing the elastic fastening means between the LED support and a surface belonging to the housing itself, which is therefore the fastening element connected to the housing, is also a possible solution according to the invention.

Here, the collimator 4 is constructed in such a way that it has optimum efficiency when the contact of the collimator 4 is flat with the support 3 of the LED 2. Breaking the plane contact between the collimator 4 and the support 3 of the LED 2 is equivalent to making a movement of rotation with respect to a family of axes perpendicular to the direction of maximum emission of the emission characteristic of the system comprising the DEL 2 and the collimator 4. In the case described here, a rotation of the collimator of more than 3 with respect to one of these axes generates a loss with respect to the maximum intensity of 10%. These rotational movements can only occur if there is a play in a direction close to the direction of maximum emission of emission of the system comprising the LED 2 and the collimator 4, between the various elements that are the support 3 of the LED, the collimator 4 and plate 10 that transmits light. The elastic material 11, the elastic fastening means, exerts a pressure on the collimator whose plane contact with the LED support 3 is then forced. Taking into account that then the elastic clamping of the collimator avoids the presence of these gaps, these rotations are prevented.

A polyethylene tape 13, a material with a low coefficient of adhesion, is inserted between the elastic fastening means that are the block 11 of elastic material and the optical means that are the collimator 4 and allows translational movements due to the differences in expansion between the various elements built from different materials. In particular, the pressure exerted on the collimator 4 by the block 11 of elastic material could block, in the absence of this material with a low coefficient of adhesion, said translational movements and therefore generate a drag of the collimator in the movements of the plate 10 transmitting light and connected to housing 1. The presence of the polyethylene tape 13, a material with a low coefficient of adhesion, frees the translational movements of the elastic material 11 with respect to the collimator 4 and thus prevents the movements of the collimator 4 with respect to the support 3 of the DEL 2.

The housing 1 is advantageously made of heat conducting material, for example anodized aluminum, and its outer surface has a corrugated surface 14. During operation, the DEL 2 emits heat. However, the optimal performance of a LED in terms of light flow mainly requires a controlled temperature: therefore the heat emitted by LED 2 must be evacuated. The heat conducting material will allow heat to escape to the outside and the corrugated surface increases the efficiency of this radiator.

Figure 2 describes an implementation of the invention inside a luminaire that includes several LED's for which the optical means are fixed according to the invention. The increase in the number of LED's imposes an increase in the size of the luminaire and, as a result, the movements due to the differences in expansion between different materials therefore have greater amplitude. The invention finds in this case a particularly interesting application.

In a housing 20 is fixed a support 21 that has a certain number of DEL 22. In each of the DEL 22, a collimator 23 is aligned and placed on the support 21. In a particular implementation of the invention, also Several collimators 23 can be grouped in a single piece placed on the support 21, the collimators each being centered on a DEL 22. A light transmitting plate 24 is superimposed on the set of collimators 23 compressing two bands 25a and 25b of elastic material. Plate 24 is connected to housing 20 by two double-sided adhesive strips 26a and 26b. Two polyethylene tapes 27a and 27b, a material with a low adhesion coefficient, are inserted between the collimators 23 and the elastic material bands 25a and 25b and allow translational movements due to the differences in expansion between the various elements, which are the plate. 24 and housing 20, constructed from different materials.

In this example, the implementation of several sets made up of a LED and its optical means requires that the luminous performance of each set made up of a LED and its optical means be homogeneous. Differences in light performance between the different sets would harm the aesthetics of the

ES 2 332 871 T3 result and / or its effectiveness. However, fixing the optimal position of the optical means with respect to the emission characteristics of the LED is particularly important to guarantee the homogeneity of the light performance of each of the sets made up of a LED and its optical means. By guaranteeing an optimal and individual positioning of the optical means with respect to the emission characteristic of each of the LED's, the invention makes it possible to consider uniform lighting in different ways, based on the emission of several LED's.

The collimators 23 have, in this example, a rectangular front surface 28 enlarged so as to exceed the strict exit surface of the light beam. This enlarged front surface 28 serves as a bearing surface for the two bands 25a and 25b of elastic material which are positioned on the sides 28a and 28b of the front surface 28 so that the luminous flux is not reduced.

As their front surface 28 is rectangular, the collimators 23 do not show symmetry of revolution. For aesthetic reasons it may then be desired to prevent a rotation with respect to an axis perpendicular to the plane defined by the front surface 28 of the collimators 23. This rotation is even more particularly damaging when the optical means do not have symmetry of revolution in order to have an output beam that also has no symmetry of revolution: said rotation then affects the luminous properties of the luminaire. This rotation can be limited by projections 29a and 29b made on the casing 20. However, in the embodiment presented in figure 2, taking into account industrial procedures used to manufacture the casing, which in this case is made of extruded aluminum, it is difficult to control the clearance between the collimators 23 and the projections 29a. and 29b. Then such rotation is only severely limited.

Figure 3 shows a partial top view of an improved embodiment of the luminaire of figure 2, a view in which the same references designate the same parts as in figure 2. The improvement consists in limiting the amplitude of movement in rotation of the collimators 23 with respect to an axis perpendicular to the plane defined by the front surface 28 of the collimator 23. For this, rigid pieces 30 are inserted into the different front surfaces 28 of the collimators 23. These rigid pieces 30 have dimensions calculated so that there are gaps between said rigid pieces 30 and the collimators 23. Indeed, the presence of the rigid parts 30 must make it possible to limit the amplitude of the rotation of the collimators 23 without making the set of collimators 23 rigid, each one must remain independent so as not to generate stress on the LED 22. In this example, the most adapted shape for these rigid parts 30 is a parallelepipedic shape that fills the empty space between two front surfaces 28 of two collimators 23 but this shape is not exclusive and can be of various kinds so that it adapts to the geometry of the luminaire and / or that of the optical media. Said rigid parts 30 can be put into practice in combination with the invention or independently of the invention.

Two projections 31a and 31b are advantageously located on each of the rigid pieces 30 to serve as a stop for the bands 25a and 25b of elastic material and the polyethylene tapes 26a and 26b shown in Figure 2. This prevents these elements from covering the part of the front surface 28 of the collimators 23 through which the light beam emerges. Said projections 31a and 31b can, in another embodiment, be made on the front surface 28 of the collimators 23.

Figure 4 represents an example of a particular embodiment of the rigid parts 30. Said rigid, parallelepipedic pieces 30 inserted between the different front surfaces 28 of the collimators 23 are in this case grouped by several, two for example, in a single piece 33 for adjusting the clearances thanks to a connection element 32 that forms a body with the set of the two rigid parallelepipedic pieces 30. Said clearance adjusting piece 33 can, for example, be made by molding all kinds of rigid material. Molding is particularly advantageous since it allows the projections 31 to be made easily.

The particular shape of this example of clearance adjusting part 33 makes it possible to limit the movements of the rigid parts 30 between the collimators 23 that could be effected in the case of independent rigid parts 30.