Luminaire having means for reducing the apparent size of the light source

April 26, 1938. t. w. rolph 2,115,178

LUMINAIRE HAVING MEANS FOR REDUCING THE

APPARENT SIZE OF THE LIGHT SOURCE

Filed July 28, 1934 2 Sheets-Sheet 1

350-411

SR

XR 2»115,178

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ATTORNEY.

350-175.LD

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April 26, 1938.

2,115,178

T. W ROLPH ^lum^aire HAVING means -for reducing the APPARENT SIZE OF THE LIGHT SOURCE

Filed July 28, 1934 2 Sheets-Sheet 2

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ATTORNEY.

Patented Apr. 26, 1938

2,115,178

UNITED STATES PATENT OFFICE

2,115,178 ^FOB REDUCING

SOURCE^{PABENT SKE} °^{F raE LIGHT}

Thomas W. Rolph, Newark, Ohio, assignor to Holophane Company, Inc., New York N Y a corporation of Delaware ’

Application July 28, 1934, Serial No. 737,375 (CL 240—106) ; Joye^^more concentrated light sources are em.T??^{e acc}°mpanying drawings show, for purposes of illustrating the present invention, several embodiments in which the invention may take form _Ktratfve^n-f¹?^⁶¹·⁸*⁰⁰^^{that the} are illusslme in ^{rather than th}e same, in these drawings:

^shows a light source with two reflectors rpfl^.f^{erent SiZe iIlustra}tmg the effect of size of ₁₀ °^Γ ξ^ροη ^ad of emerging light beams; ^{1 shows a} hght source with two refractors ^dl®^{erent Slze} illustrating the effect of size of

Γ ^{spread of eme}rgmg light beams;

Fig. 3 shows, m cross-section, a vapor-tube light source with elements of a refractor, illustffiinf £^{eduction of} spread when the’direction of the beam is altered;

Fig. 4 is a fragmentary cross-sectional view of a luminaire for a horizontal tubular light source with refracting side plates employing the refracting elements of Figure 3 to reduce the apparent size of the Source; ^P^a Projector designed to reduce the spread of the emitted beam,* _bl?jtA^Sh° ™ ^a construction similar to that illustrated in Fig. 3 but with the two refracting elements spaced a substantial distance apart!

Fig. 7 shows how the spread of the emitted light may be reduced even when there is no net change in the direction of the light passing through the refracting elements. ^S

It has been stated above that the degree of concentration obtained is partially a function of the ntht ^the^^ht. controlling medium from the hght-source. This is illustrated in Fig. 1 which fleeter ^lam? / ^{With hght}‘^source 2, small reflector 3 and larger reflector 4. Light rav 5 strikes the small reflector at point 6 and is re^show?· ^{If the} small reflector were not ^^d· ^{lght ray which} may then be called would strike the large reflector at point 8 and be reflected as shown. The direction of fho reflected light is the same in the two cases since slope at 8 is the same as at 6. With the small reflector, the angle included between the point of reflection 6 and the extremities of the light soutpp 9 and 10 is 10» in the example illusSted S! 10°^e' iJ^eth^Pread °Ll^{he reflected light} is also 10 . In the case of the large reflector, it is obvious from the construction that the angle of light included between the point of reflection 8 and the extremities of the light-soS 9 anj

Claims.

This invention relates to luminaires having means for reducing the apparent size of the light source whereby one can obtain an emitted beam °^f u ^{having a} iesser degree of spread than would be obtained with the usual refractors or reflectors. The invention is applicable to luminaires from which a considerable concentration of light is expected. With such luminaires, the application of this method of refracting the light will produce more concentrated b^aar?^s and sharper cut-back from the center of the beam than could otherwise be obtained. In effect, the apparent size of the light-source is reauced.

According to the present invention the light is caused to pass through a succession of refracting elements so disposed that the refraction at the inner (or incident) surface of each refracting element is greater than that at the outer 20 surface of the corresponding element. This brings about a cumulation of the condensing effect of each refracting element.

In light projectors or luminaires in which a - °,^f. ¹?^{ht is produced}> the minimum spread > of the light beam is ordinarily dependent upon the size of the light source and the distance of Hi® ^{hght redir}ecting medium from the source. With past equipment designed for maximum concentration of light, these two factors have been, for practical purposes, the only two affecting the degree of spread obtained from the oesim. - ..

In general, the size of the light source is determined by the characteristics of the type of lamp used. Lamp designers, in certain cases, try to obtain the most concentrated source possible but there are certain limits beyond which they cannot go and even to go to these limits may involve sacrifices in efficiency, life or other characteristics of the lamp. In the case of electric incandescent filament lamps, sources which are quite small can be obtained, but even these are not as small as sometimes is desired. In the case ^incandescent vapor lamps, the size of the light giving body is necessarily much larger than it is in filament lamps. The increased size of the light source greatly increases the divergence of light beyond what it would be with concentrated sources, and hence the same concentration is not ordinarily available. The present invention, by providing a new arrangement of light controlling means, overcomes the objectionable spread of light from these large sources J and brings it into angles comparable with those i

2,115,178 is smaller than in the case of the small reflector. Actually this angle Is 6° in the figure shown. Therefore, the spread of the reflected light from a given point on the reflector is only ₅ 6° with the large reflector as compared with 10° for the corresponding point on the small reflector.

The action is similar in the case of refraction of light. Fig. 2 shows a lamp 11 with light source 10 12 and small refractor 13 and large refractor 14.

Light ray 15 strikes the small refractor 13 at point 16 and is refracted into the direction indicated. If the small refractor were not used, the large refractor would intercept the same light 15 ray now numbered 17 at point 18 and this light ray would be refracted in direction shown. This direction is the same as refracted ray 15 from the small refractor, the two refractors being identical in design. The angle of light included 20 from point i 6 to the extremities of the filament is in this particular illustration 10°. Therefore, with ordinary methods of refraction, the spread of the light beam emerging from point 16 is also 10° or 5° each side of the light ray 15 shown 25 emerging from the small refractor. In the case of the large refractor the spread of light from point 18 to the extremities of the light source is less than in the case of the small refractor. This is obvious from the geometrical construction 30 in the figure. The actual spread in this case is

6°. Hence, the light emerging from point 18 on the large refractor will have a spread of 6° or 3° each side of the central emerging light ray Π. This shows how the increase in size of a re35 fractor reduces the spread of the emerging light beam.

However, it is expensive and often impossible to make the size of a reflector or a refractor, for concentrated light sources so large that the 40 spread of the emerging beam is as small as de-, sired. The difficulty increases enormously with large sources such as vapor tubes. Instead of occupying an angle of less than 10°, (which is easily obtained with concentrated sources) it may 45 occupy angles in the neighborhood of 30°, or more. If ordinary light control is employed, the minimum spread of the emergent beam would be the same high angle, resulting in poor concentration and absence of sharp cut-off.

In Fig. 3 the light source 19 is large in size representing in cross-section a tube of incandescent vapor. A section of a refractor to redirect the light from this source is shown at 20 and 21, 20 being an inner piece and 21 an outer 55 piece. A typical point 22 on the inside of the inner piece receives light from the center of the source represented by light ray 23 and from the outer edges of the source represented by light rays 24 and 25. In the particular figure shown 00 the spread of each of the extreme light rays from the central light ray is 15°. Since light ray 25 strikes the surface 20α at 22 at a greater, angle of incidence than light ray 23, it will receive greater deviation in the refracting medium than 05 light ray 23. Similarly light ray 23 will receive greater deviation than light ray 24. Therefore, the three light rays in the glass will be brought closer together and the spread of 15° each side of the central light ray will be reduced. In the ar70 rangement illustrated, the spread is reduced to

8.1° above the light ray 23 and 9.3° below- the light ray 23, or a total spread of 17.4° in the glass 20. In order to obtain the maximum advantage irom this reduction in spread of light, the outer 75 surface 20b of the inner refracting piece is given a slope which will produce as little refraction as is possible. The slope selected is such that central light ray 23 when emerging from the outer surface of the inner piece will suffer no refraction at all. Light rays 24 and 25 are refracted r slightly away from light ray 23 but this refraction is not as large as that obtained at the point 22 on the inner surface and therefore, the net spread of the light emerging from the inner piece of glass is less than when it entered the glass. ₁₀In the arrangement shown, the spread of light in the air between the two pieces of glass is 12 3° above the central light ray and 14° below the central light ray or a total of 26.3°.

This process is now continued with the outer i₅piece of glass or refracting medium. The angle at which the light strikes the surface 21α of this outer piece is such that a considerable degree of refraction is obtained for the central light ray 23. The limiting light rays are also refracted 20 25 being obviously refracted more than 23, since the angle of incidence is greater for light ray 25 than for light ray 23. Similarly light ray 24 is refracted less than light ray 23 because its angle of incidence is less than the angle of in- 25 cidence of fight ray 23. Consequently within the ' medium 21, the spread of light is still further reduced and in the case illustrated, it becomes 4.6° above light ray 23 and 6.9° below light ray 23, or a-total of 11.5°. The outer surface 2!b 30 I of this medium is placed normal to the emerg- 1 ing fight ray 23. Consequently, there is no re-I fraction as this ray emerges from the medium.I

There is inevitably some spreading action for the'' two extreme rays 24 and 25 but this spreading 35j action is much less than the condensing actionI at the inner surface because the angles of in-I cidence are much lower. As a result, the spreadί of the emerging light is much less than the’ spread of the entering light. In the case shown, ₄₀the actual spread of .light ray 25 above light rayj is 7° and the actual spread of light ray 24 below light ray 23 is 10.5°. Therefore, this particular combination of refracting prisms has reduced the spread of light from the original source λκ from 30 to 17.5°. This amounts to a reduction in the apparent size of the fight source. To obtain the same angle of spread by former structures would mean a great increase in distance of refractor from source or a great increase in size _Knof. refractor similar to that shown in Fig. 2.

It is not necessary to have the central emerging light ray always leave the outer surface at the normal to that surface. Some useful redirection of light will often be desired at the outer 55 surface of one or both pieces. This will lessen the condensing action but some condensation will be obtained, as long as the refraction at the inner surface of each piece is greater than at the outer surface. _βθ

Reduced spread of the emerging light has several definite advantages. It ‘increases the concentration of light and this increase in concentration is added to whatever concentration may be obtained by the lenticular effect of the prism de- 65 sign. It also makes possible what is known as a sharper cut-off . In many lighting problems, it is desirable to have the luminaire give this sharp cut-off in order to project as much light as possible in a given direction with as little light as 70 possible in a direction a few degrees away from the first. For example, in street lighting, the spread of light up and -down the street must be at high angles because of the considerable distance between luminaires; at the same time, if 75

2,116,178 the beams of light are directed at too high an angle, they enter the eyes of the users of the street and cause annoying glare.' It is desirable to direct the beams at a high angle and to have the cut-off sharp so that a few degrees above the beam angle the candlepower has dropped to a low figure which will not produce such glare.

Fig. 4 is an illustration of the application of this principle to design for a street lighting luminaire. In tills figure, 26 represents in crosssection a tubular light source of appreciable size. 27 and 28 represent side plates each comprising two pieces of glass or. other refracting medium provided with prisms as illustrated in Figure 3. The result is that a high degree of concentration is obtained at the particular angle desired. In this case, the angle of maximum candlepower is 75° to nadir or 15° below the horizontal. From the discussion of Fig. 3, it will be obvious that the concentration of light obtained at 75°. will be considerably greater with this system.of refraction than with systems ordinarily used. It will further be obvious that the candlepower will decrease very rapidly above 75° becoming negligible at the angles close to the horizontal which are likely to be directed toward the eyes of users of the street.

Fig. 5 shows a projector designed to obtain a single circular beam of light with reduced spread. In this case, an incandescent filament lamp 32 is shown with light source'33 in the form of a small straight filament. Even though the lamp manufacturer may make the filament as small as possible, there is some size to it and this size tends to give a spread to the emerging beam. However, by means of the condensing action of the refractors described herein, this spread can be greatly reduced. In the structure shown in Fig. 5, three successive refractors are used, 34, 35, and 36. A light ray 37 near the extreme edge of the structure is refracted successively by the three refracting pieces to emerge in the beam direction. The refraction in each piece, however, is obtained at the surface at which the light enters. The surface at which the light leaves the article is set to be normal to the direction of the emerging light ray. There is, therefore, no refraction of light ray 37 at the surface at which it emerges from each piece of glass. The extreme light rays 38 and 39 from the edges of the filament striking the same point as light ray 37 on the inside of the inner piece are refracted as described under Fig. 3 and when emerging from the final piece of glass are spread from light ray 37 to a much lesser degree than when striking, the inner surface of the inside piece 34. With light ray 40, the refraction is less than with light ray 37 because 40, on emerging from the light source, is nearer to the direction of the final beam of light. Hence, the condensing effect of this system of refraction is less with the light from the source striking the inner piece at the point at which light ray 40 strikes. However, this condensing effect is still sufficient to be valuable. Light ray 41, representing the light ray going through the center of the device, suffers no condensing effect since there is no refraction. With this particular design of filament, however, in the form of a short line of light, no condensation is necessary at 41 because the cross-section of the filament perpendicular to this direction is substantially a point. In this particular type of design, it'is very valuable to have a light source in the form of a short line coinciding with the axis of the system. With this type of light source, the condensing action is greatest where it is needed the most, represented in the figure by light ray 37. It is lesser in degree where it is needed less, represented by light ray 40 and least of all where it is not needed, represented by light ray 41. The general scheme of a projector utilizing this system of refraction may, 5 however, be applied to any light source.

This type of projector may advantageously be supplemented by a spherical reflector 42. This will return the light rays striking it back through the source to be acted upon by the refracting 10 pieces in the same way as the light striking them directly. :

Since several refractions are frequently necessary to get a desirable condensation of light, it is possible to turn light into the desired direction 15 even though it emerges from the light source at a large angle away from this direction. In Figure 5, a large angle of light is included by the refracting system and when this is further supplemented by the spherical reflector, an optical 20 system of very high efficiency is obtained considered from the standpoint of the amount of the original light acted upon.

It will be understood that the invention is not confined to the use of two or three successive 25 refracting plates or articles. Any number may be used. Two or three will probably satisfy most requirements but certain problems requiring the most extreme concentration may require more than three successive refracting articles. 30

Fig. 6 illustrates a refracting arrangement similar to that shown in Fig. 3 but with the two refracting elements spaced apart a distance greater than is necessary for mechanical clearance. It is sometimes desirable to use a con- 35 struction of this character and it frequently carries with it certain optical advantages. In this figure, 48 is a light source of considerable size. A light ray from the center of the source is shown at 49 striking the point 58 on the inner refracting 40 element. A light ray 51 proceeding from the center of the source, at a higher angle than 49 strikes the inner refracting element at a point above 50. Similarly a light ray 52 also proceeding from the center of the. source in a direction lower than 45 ray 49 strikes a point on the inner refracting element lower than point 50. In a construction of this kind, it is common to have a large amount of the light which emerges from the structure concentrated at the same angle. In street light- 50 ing, for example, this angle usually is 15° below the horizontal. Therefore, light ray 51 must receive a greater degree of refraction than light ray 49. Similarly light ray 52 will receive a lesser degree of refraction than light ray 49. 55 Consequently the prisms will grow progressively deeper from bottom to top of the structure. This prismatic, change may be in both pieces or in only one piece, but in the present instance, it is desirable to make as much progressive change 60 as can be conveniently made in the prisms of the outer prismatic piece. Therefore, light ray 49 striking the outer piece at point 53 receives a certain degree of deviation at this point whereas light ray 51 striking the outer piece at point 54 above 53 65 must , receive a greater deviation and light ray 52 striking the outer piece at point 55 must receive a lesser degree of deviation. The prism at 54, therefore, gives greater refraction than the prism at 53 and the prism at 53 gives greater 70 refraction than the prism at 55. Considering now the light rays 56 and 57 proceeding from the outer limits of the light source and striking point 50, it will be clear that light ray 56 striking the outer refracting piece at point 55 suffers less 75

2,118,178 refraction at this point than light ray 49 striking the outer piece at point 53. This tends to reduce the spread between light rays 49 and 56. Similarly light ray 57 striking the inner piece at δ point 59 strikes the outer piece at point 54 and suffers a greater degree of refraction than light ray 49. Thus, the greater the space between the two refracting elements, the greater will be the additional condensing effect obtained by the pro10 gressive change in prisms on the outer piece.

It is not necessary to have the inner and outer pieces parallel. Sometimes, for mechanical or optical reasons, the two pieces will slope or curve away from each other, coming close together at 16 certain points and being far apart at others.

In any part of the structure where the spacing between the two parts exceeds that necessary for mechanical clearance advantage may be taken of this additional condensation obtained by the 20 progressive change in the prisms. Frequently it is possible to use this to obtain additional condensation of light where it is most needed and yet retain normal spacing between the two pieces wherever that is mechanically advantageous.

In Fig. 5 it was noted that the direction of light ray 41 was not changed by the refracting system. No condensing effect was obtained by the refracting system at this point. It is possible, however, to utilize this scheme of refraction and obtain a 30 condensing effect at an angle at which no redirection is to be obtained. This is illustrated in Fig. 7. A light source 44 emits light ray 45 which is to go through the refracting system without any net change of angle. However, the inner sur- face of the first refracting piece is set to give a considerable degree of refraction to light ray 45. The outer surface of this inner piece is set to give little or no refraction to light ray 45. Then the inner surface of the second piece is set 40 to refract light ray 45 back to its original direction and the outer surface of the outer piece is set to allow this light ray to emerge without refraction. Therefore, the light ray from the center of the light source is refracted by the inner piece 45 away from desired direction and is refracted by the outer piece back to the desired direction. Light rays 46 and 47 represent the light rays striking the inner piece at the same point as 45, but coming from the extreme limits of the light source. These undergo the same refracting effect as illustrated in Fig. 3 and emerge from the inner refracting piece at a lesser angle of spread from the central ray than when they enter. In passing through the outer medium, the same con55 densing effect occurs even though the direction of refraction is opposite from that obtained with the inner piece. Consequently the light rays 46 and 47 emerge from the refracting system at angles from the central ray 45 which are less than 60 the corresponding angles from 45 on the entering side, yet light ray 45 has suffered no net change in direction.

Thus, this system of refraction for obtaining a condensing effect may be utilized by means of 65 refraction in the same direction from two successive pieces of glass or refraction in opposite directions from the two successive pieces. In either case, the desired effect is obtained.

It will be understood that this system of re70 fraction may be utilized in luminaires of varied character. Whenever concentration of light is desired, this system is a possible means of obtaining a- better effect than would otherwise be obtained. The system is not limited to any par76 ticular type of light source or to any particular field of lighting or to any character of luminaire.

It is obvious that the invention may be embodied in many forms and constructions within the scope of the claims, and I wish it to be un- 5 derstood that the particular forms shown are but a few of the many forms. Various modifications and changes being possible, I do not otherwise limit myself in any way with respect thereto. 10