US1458635A - Headlight screen - Google Patents

Description

June l2, 1923. v $458,635 L. F. WHHTNEY HEADLIGHT S CREEN Filed Oct. 25, 1920 3 sweets-sheet 1 June 12, 1923.

L. F. WHITNEY HEADLIGHT S CREEN Filed oct.

25. 1920 3 sheets-sheet 2 .Perceffaye ef Z607.

June` l2, 1923.

l. F. WHITNEY.

HEADLIGHT SCREEN Filed Oct. 25, 1920 3 Sheets-Sheet 3 406597665' 7706723071 Z 527760717. Mii/627e 2;

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Patented dune l2, lQdQ LYMAN W.

WHITNEY, 0F BSTON, MASSACHUSETTS, ASSGNOR T0 KALEUS @Oldt- STOCK dz VIESCGTT, ZINC., OF BOSTON, MASSACHUSETTS, .l GRZPORATEGN F MASSACHUSETTS.

H'EADLIGET SCREEN.

application iled Uctober 25, 1920. aferial No. lala-4l.

T 0 @ZZ whom t may concern.

Be it'known that l, LYMAN F lVHITNnY, a citizen of the llnited States, and resident of Boston, in the county of Suffolk and State ot' Massachusetts, have invented new and useful lmprovements in l-leadlight Screens, of which the following is a specification.

My invention relates to a multiple reflecting translucent screen of a type particularly adapted for use with automobile headlights or lights ot that character used for other and/similar purposes.

Automobile headlights of types now in general use comprise a parabolic rellector with a source oflight such as an incandescent bulb laced in the focus of the reflector. Such a light will theoretically deliver' a beam composed of parallel rays. ln practice it does not deliver such a beam but delivers a cone-shaped beam `comprising an inner smaller cone consisting of the reflected light and an outer cone consisting of direct rays from the light source, the outer cone 25. belng limited in size only by the opening in the front ofthe reflector. rlhe reflector rays are cone-shaped rather than parallel due to the fact that the' reflector is not a perfect parabola and the source of light isnot a theortical point, and therefore even ifa portion of the filament is located at the exact focus, other portions extend outside that point. Y

ln the practical use of such lamps for automobile headlights the lighting effect desired is illumination of the roadway to as great a dista-nce as is commensurate with the strength'of the light, without the emission of blinding rays extending above the plane of the lamp itself. This latter requirement is caused by the' :tact that intense rays extending upward will'blind drivers of approaching vehicles or pedestrians and be a4 source of danger and of accidents. Moreover, the use of headlights Without illumination so restricted is prohibited by law in many jurisdictions.

rlhe light to be most desiredtherefore is one which presents a sharply defined upper boundary with intense light immediately adjacent the upper boundary since it is this light whichwvill be directed substantially parallel to the road and which will be useful for illuminating purposes, at the eXtreme range of the light.

ln so far as l am aware the only effective sultsis by means of the utilization of the principle of total reflection as described in the patent of Daniel F. Comstock No. 1,377,- l8l, granted May l0, 1921. j

rlhe utilization of the principle oi total reflection permits of a sharp line of cleavage between the rays directed inside the critical angle of the lens or screen-usedand those impinging thereon outside lof the critical angle. These two classes of rays may be vreadily separated and either class .rna'7 be utilized for illuminating purposes, giving a beam sharply defined on one side.

lllowever, the prior utilizations of this principle made use of but a single total reflection, which methodhas certain undesirable results. The phenomena of total re `lection are such that, while all rays incident at angles greater than the critical angle are reflected, not all rays incident at angles less than the critical angle are transmitted, but a certain portion of these latter rays are also reflected. Therefore if the screen utilizes the reflected rays, it projects all of the rays outside the critical angle, but it also projects some rays which are inside the angle and consequently the resultant beam has some upwardly extending rays. @n the other hand, if the screen utilizes only the transmitted portion of those rays incident at less than the critical angle, it does not secure all the rays inside the angle since portions of such rays are reflected. Since the percentage of relected rays is greater adjacent the critical angle and it is the rays at this point which should form the brilliant upper portion adjacent the boundary or the beam, the loss of eihciency in the light is quite marked.

lt is an object of my invention 'to provide a new and improved translucent screen `especially adapted for use with automobile of Fig. 1;

or to render non-blinding substantially all rays havin other directional characteristics. It isa so an object to provide a screen which will produce a beam of light having a sharply defined boundary upon one side and having substantially its maximum illuminative effect adjacent this boundary. It is another object to provide a screen which will permit the utilization of the greatest possible proportion of the light energy of the light source without producing a light having any intense rays so directed as to be blinding in their effect. Other and further objects will appear as the description proceeds.

I have illustrated certain preferred em bodiments of my invention together with diagrams illustrative of the principle of the invention with accompanying drawings in which,

Fig. 1 shows one form of my screen as seen from the rear, the rim being partly broken away;

Fig. 2 is a vertical section on line 2-2 Fig. 3 isa of Fig. 1;

Fig. 1 is a detail View showing the action of the screen illustrated in Figs. llto 3;

Fig. 5 is a view similar to Fig. 1showhorizontal section on linev 3 3 ing another embodiment of the invention;'

Fig. 6 is a vertical section on line 6 6 of Fig. 5;

Fig. 7 is a horizontal section online 7 7 of Fig. 5;

Fig. 8 is a detail view showing the action of the screen illustrated in Figs. 5 to 7;

Fig. 9 is a vertical longitudinal section through a headlight having Ia double-reflection screen;

Fig. 10 is a detail view showing the action of the screen illustrated in Fig. 9; and

Fig. 11 is a diagram illustrative of the principle of my invention.

In the form of my invention shown in Figs. 1 to 4., the screen consists of a face plate 7, having the reduced circu-mferential portion 8, andihaving its outer face formed with the vertically extending cylindrics 9 which meet to form the ridges 10. This plate is 'held in frame 11 by the flanges 12 which are bent down against the reduced circumferential portion 8 of the plate. The

opposite .edge of the frame carries the flange 13 adapted to be utilized in connecting the frame to a lamp or the like. Fitting against the plate v7 in the frame 11 are the trapezoidal prisms 14 which are similar in cross-section but which vary in length as shown in Fig. 1 in order to lill the .circular frame. The Arear faces of the prisms 14 slope upwardly and rearwardly. the purpose of which will be discussed hereafter.

he spaces 15 formed at the end of the prisms may be filled with cement or any suitable filler in order to maintain the prisms positively in fixed relation. Thin sheets of translucent paper or similar material 30 may be placed between the adjacent 'faces of the several prisms or there may be placed between these surfacesany material, or the surfaces may be coated with a film of any material, adapted to diffuse, absorb or otherwise obstruct any light passing through the surfaces, the surfaces themselves, regardless of the external element of treatment, serving to totally reflect all light -impinging thereon at angles greater than the critical angle and a smal within that angle. l

The screen shown in Figs. 5 to 8 is similar to that shown inFigs. 1 to 4 in that it comprises a rim 11', a front glass 7', and transverse prisms 14 separated by light obstructive layers of paper or aluminum or other suitable material. the prisms being mounted in the rim by suitable material as shown at 16. However, instead of the prisms being inclined on their rearward surfaces as shown in Figs. 3 and 4, their rearward surfaces are all disposed in the same vertical plane and the forward faces 'are inclined., Moreover, instead of the cylindrical surfaces being formed on the front of the glass 7 they are formed on the front of the prisms. Cbviously the cylindrical or` light spreading surfaces might be placed on the rear face of either the 'prisms or front glass.

In Fig. 9 I have'shown a headlight of the usual type comprising the shell 16, the reflector 17, electric bulb 19 with filament 20, the shell having a flange 18 co-acting with the flange 21 on the frame 22, which latter contains the plates 23 and 24; carrying the oppositely faced, interfitting prisms 25 and 26 respectively.. The plates are so placed as to provide the spaces 27 between the oblique faces of the prisms and thesev spaces may be treated in the same manner as was described relative to the adjacent faces of the prisms shown in Figs. l to 8. The 'outer face of the plate 23 is provided with vertical concave c vlindrics 28 similar to those provided on the cuter plate 7 of the other forms of the device.

My invention. in each of its forms just described in some detail, is designed to utilize the reflected light, that is the light totally reflected by the oblique prismatic surfaces of the screen. As has been. stated, all light is reflected which impinges upon the reflecting surfaces at an angle greater than the crit-ical angle, which angle in glass such as that normally used for such screens, is approximately 41 8', the index of refraction being approximately 1.52. 0n the other hand. some of the light impinging at less than the critical angle is also reflected and the relative amount is substantially as l portion of the light'y Cil lessees shown in Fig. il. ln this figure the ordinates represent percentages of the totalV light which is reflected and the abscisszc represent angles ofincidence in degrees?l the zero in the scale being the critical angle. 'llhose degreeson the left of the scale in dicate angles greater than the critical angle7 and as the curves show all such light is reflected. The degrees to the right of zero indicate angles less than the critical angle and they are therefore marked as negative angles. The curve A represents the light reflected upon a single reflect-ion, the curve B upon a double reflection and the curve C upon a' quadruple reflection. rl`he meaning of these ,curves and the effective result of the facts they indicate may perhaps be made more clear by considering a. concrete example.

ssuming that a single-reflection critical-angle reflector (as disclosed e. in the aforesaid Comstock patent) is p aced at such an angle that all light impinging thereon at the critical angle is reflected horizontally and all rays impinging thereon at angles greater than the critical angle are reflected at corresponding angles below the horizontal. it is clear from curve 'A of Fig. l1, that although-there will be a pronounced drop in the intensity of the light at the hoiiaontal plane,v nevertheless more than 30% of the light reaching the critical angle reflector at 1 less than the critical angle will he reflected and will be inclined upwardly 1. Similarly more than 20% of the reflected light will be directed upwardly 2", and even at 50 within the critical'angle 10% of the light will be reflected. ltf'will readily be understood that in the case of a high-powered headlight even 10% of its light energy will produce ablinding light and light directed upward through 5 and starting from the level of the usual automobile headlight will extend upward sufliciently to blind a pedestrian or driver quite close to the light.

Considering' this curve A from the oppof site `view point and taking it in connection with those types of critical angle reflecting screens which utilizes the transmitted or non-reflected light, the area below the curve represents the light lost. and since the most intensel and useful light is that directed nearest the horizontal it is apparent that such screens leave something to be desired from the point of efficiency.

llut if. instead of using a single critical angle' reflector a plurality of such reflectors are arranged in succession, as illustrated in the drawings for example. `the. percentage of light which passes through the screen within the critical angle is greatly reduced. as shown in Fig. ll where the curverl shows the amount of such light in a mul-A tiple-refiection and curve C in a quadruple reflector such as illustrated in Figs. l to l of such light passing through as in a single reflecting screen lonly about passes through in a double reflectingscreen and practically' none passes through in a quadruple reflecting screen. lt 'therefore appears that a. multiple reflecting screen is far more effective in eliminating upward glareat the same time the intensity of the beam at and near its 'upper boundary,` and consequently its effectiveness to illuminate thedistant' roadway. is extraordinarily effective.

The action of the screen shown in Fig. 9 is illustrated in the diagram of Fig. 10. rlhe ray a entering along the horizontal impinges upon the total reflecting oblique surface of the prism 26 at substantially the critical angle and is therefore reflected. lt passes down through the lower horizontal face of the prism 26 and the upper horizon, tal faceof 'the adjacent prisrn -2'5 of the' other series at angles lessth'an the critical angle and is transmitted. lt then impinges upon the oblique surface of the prism at an angle greater than the critical angle and is reflected, the several angles of the prisms being proportioned so that it passes forward substantially horizontally. Obviously all rays reaching the original reccting surface at an angle greater than the ray discussed, will be acted upon in the same manner.

Hou-'even rays such as indicated by t) of Fig. l0 which impinge upon the original rcilecting surface 20a at angles less than the critical angle will be largely transmitted through said surface and only in small part reflectedbv this surface as indicated by the curves of Figli. Taking as being 5o less than the critical angle. at the first surface substantially 9057? will be transmitted and 10% reflected. 0f this 10F/f which is reflected. when it reaches the second reflecting surface 26h. 90% of it. or 9% of the original light, is transmitted leaving 1%of the original intensity to he reflected forward and upward at 5c above the horizontal. as shown by the curve B of Fig. 6. Except in very strong headlights. lF/f of the intensity will not be sufficient to he blinding. fm'isiderinLr now the 90%' of the original ray 7) which was transmitted through the first reflecting surface, this light is obstructed by one of the methodsdisclosed, and is preferably didused by a non-transparent film, such as a sheet of paper interposed between the two prisms,

the thickness or light transmissive quality ofthe film or sheet of paper'depending upon the intensity of the light with which it isto he used. The9% ofthe original light which is transmitted through the second reflecting surface is diffused by the film between that surface and the adjacentl one. It even a sharper cut-oil' is desired than that given by a double reflection the form ot' my device shown in Figs. 1 to 8 which gives four reflections may be used.

The action of the screen shown in Figs. 1 to '3 is illustrated in Fig. 4. Li ht entering from the rear (the left 1n Fig. 4 is reflected as indicated by ray C if it strikes the critical-angle reflecting surface outside the critical angle; otherwise most of it passes through the critical-angle surface (as shown by curve A in Figll) and is either absorbed or diffused or otherwise obstructed depending upon the material 30 placed between the prisms.

entering the' prisms horizontally is incident at substantially the critical angle, e. g. just inside the critical angle, then "substantially no light is projected vl'rom the headlight above the'horizontal. By inclining the rear faces of the prisms as shown, the light-is bent down upon entering the screen. whereby each ray leaves the screen in a lower di rection than it enters. lin this way rays which are upwardly inclined before entering the screen may be transmitted and projected in or below a horizontal direction, thereby increasing the efliciency of the screen without decreasing its remarkable non-glare qualities. The light issuing from the screen is spread by the cylindrical surfaces 9 on the cover glass 7.

The operation of the embodiment shown in Figs. 5 to 8 is similar to that of the first embodiment, but the light is bent downward upon leaving the prisms instead of upon entering and the spreading surface is located on the forward lace of the prism instead of on the front face of the cover glass. Thus both the front and the rear' faces ot the screen are dat and smooth.

In a double-reecting lens such as shown in Fig. 9, the following arrangement (hereinafter referred to as the principal example) has been found satisfactory. The criticalangle reecting surfaces are set at such angle to the vhorizontal that the'horizontal rays are incident to the reflecting surfaces 1o within the critical angle, thuspermitting approximately 11% of such rays to be projected (s'ee curve B in Fig. 6). ays inclined above the horizontal 1o are incident to the reflecting surfaces 2O within the critical angle and only approximately 6% of such rays are projected. And rays inclined downwardly only 1o are substantially 100% projected inasmuch as they are incident at the critical angle.

lf the horizontal rays above referred to are the parallel rays of the light beam., i. e., the rays parallel to the axis of the reflector, which are the most edective rays, it is obvious that these rays are largely obstructed,

if the criticalangle refleeting surfaces be so inclinedthat the light thereby reatly lowering the eliiciency of the headlight for distant illumination. However, the present invention is adapted to produce the shar cut-'oil at the horizontal (or lat any ot er desired elevation) and at the same time utilize these most effective rays to much greater advantage. This may be accomplished in several ways of which the following are examples tirst, by bending all the projected rays downwardly, say 10 before reflection (Figs. 1 to t); secondly, by bending the reflected rays downward after redection (Figs. 5 to 8) in which case the critical angle Vsurfaces are inclined at a lesser angle to the horizontal than in the principal example, say 1 less; thirdly', by placing the critical angle 'surf aces as in the principal example and then tipping the paraboloidal reflector so that vits axis is inclined 1o below the horizontal, without tipping the screen; and fourthly, by tipping the entire headlight including both the paraboloidal vreflector and the screen downwardly say 1o and at the same time inclining the critical angle reflecting sur- :laces at a lo lesser angle to the axis of the headlight than in the principal example; etc. ln each of these four cases the line or plane or boundary of the top of the beam would remain unchanged in position, e. g. assuming the upper boundary of the projected beam horizontal in the principal example, it would be horizontal in each of the four cases mentioned.

When employing light-dit'using layers between, the prisms, as torexarnple strips ci paper, the upwardly directed light which is transmitted through the critical angle reflecting surfaces is very useful as diduse'd light to illuminate the sides ol' the roadway and to makethe headlights visible at points above their level, but is not of sullcient intensity to be blinding.

Although l have described my invention as utilized in connection with an automobile headlight, it is obviously of much broader application. lt may be used in any situation where a light having a sharply defined boundary is desired, as for example in ilood lighting of signs or buildings and in other situations demanding light of similar characteristics.

l claim:

l. A screen for headlights comprising transparent media having total-reflecting surfaces lfor transmitting light therethrough by successive reflection from said surfaces, and light-obstructing means behind said surfaces for ,substantially preventing direct transmission of light passing through said surfaces.

2. A translucent screen for headlights or the like having total-reflecting surfaces arranged to reect a plurality of times and transmit without substantial diminution light incident to said surfaces at angles surfaces set at oblique angles to' the plane greater than the critical angle, the screen of the screen and having means placed behaving means t0 diffuse light incident to said tween said juxtaposed surfaces adapted to E@ surfaces at angles less than the critical obstruct light passing through said surfaces. 5 angle. Signed by me at Boston, Massachusetts,

3. A translucent screen for headlights or .this lth day of @ctober 1920. the like having juxtaposed total-reeeting LYMAN'F. WHlTNEY.

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