US2297124A - Lighting fixture - Google Patents

Description

Sept. 29, 1942. Yv. @ANDERSON ET AL 2,297,124 I LIGHTING FIXTURE Filed March asf 1940 5 snags-sheet 1 ATTORNEY .3? ./Q Q3 v Sept. 29,1942. we'. 'ANDgRsoN Erm, f -A2,297,124 v LIGHTING FIXTURE v Filed Maren 29, 1949 5 'sheets-sheet 2 ATTORNEY Sept 29, 1942. l v. G. ANDERSON r-:TAL 2,297,124 I 5' sheets-sheet 5 ATTORNEY Sept. 29, 1942.

v; G. ANDERSON ETA;

- LIGHTING FIXTURE Filed March 29, -1940 1 l5 Sheets-Sheet 4 ATTORNEY Sept. 29,11942. v, G. ANDERSON Erm. 2,297,124 LIGHTING FIXTURE Filedarch 29, 1940 5 sheds-snoei s ATTORNEY 'lighting fixtures Patented Sept, 29.1942

UNITED STATES PATENT V,ori-rca Victor Geist Anderson, New Rochelle, and Edward Rambusch, Brooklyn, N. Rambusch Decorating Company,

YL, assignors to New y York,

NfY., a corporation of New York Application March 29, 1940, Serial No. 326,546 9 claims. (ci. 24o-fis) The present invention relates to lighting fixtures, and is more particularly directed toward intended to be mounted in or on the ceiling and for producing controlled lighting in restricted working areas below the fixtures.

The present invention contemplates lighting fixtures in which the upward component of light produced by the light source (with or without an luminaire the upwardly :acting reflector below the source) is directed downwardly by reectors of such contoury as to produce a controlled symmetrical distribution of light. The fixtures contemplated 'by the 'present invention employ reectors with as high a degree of specular reflection as possible in commercial materials, and the. disposition of the reflecting surfaces and light source -are such that the desired spread and distribution of light is available. -These reflectors and the light source are'suitably screened so that direct observationV of surfaces of substantial brightness is-avoided. The source of the illumination may for practical purposes be completely concealed at ordinary'angles of observation. .l

Where one desires to accurately control and distribute light from l small sources, such as the tungsten lamp iilament, by reflection, the reflecting surfaces must have proper focal relations with the light source for otherwise the reflected rays scatter into uncontrollable angles. The parabolic reflector, which has the ability to collect light rays from a concentrated source at the focus and project them in a beam of parallel rays,

, is suitable for projection work, out is unsuited for illuminating extensive working areas, because it is impossible in a fixture of reasonable size to cover an extended working area. The ellipse has the well-known characteristic originatingat one focus and reflecting it convergently toward the other focus.` It continues divergently and may be made to, cover an area substantially greater than the area of the reflector itself;

With light sources such as the pendent, bowl silvered lamp, or the incandescent lamp bulb with specular spherical reflector underneath, practically the entire output of the lamp is directed ofcollecting light l above the horizontal and at substantial anglesl from zenith so that nearly all the lumen output is within the zone from 90 to 150 degrees above nadir. The available light is therefore substantially all concentrated into a 60 degree zone immediately above the horizontal. The present invention contemplates the provision of a luminaire having reflectors of elliptical contour (or a very close approximation thereto) adapted to inter- Von the desired area with angle cept light in this region and reflect it downwardly at suchangles as to produce downwardly directed light of adequate divergence to cover the desired working area. Where no light from the source goes directly to the Working area .below the spread and distribution is under the control of thereectors, without admixture of direct light. By proper selection of the location of the conjugate foci of the reflecting areas and the light output'I handled by'them the spread of the light may be controlled to place the light either a very even intensity of illumination, or marked asymmetry.

Other and further objectsl will appear'as the description proceeds.

The accompanying drawings show. for purposes of illustrating the present invention, several embodiments in which the invention may take form, it being understood that the drawings are illustrative of the invention rather than limiting the same.

In these drawings:

Figure 1 is a diagram illustrating the functioning of a series of elliptical reectors with fixed foci and varying eccentricities, and also the functioning of angularlyccontiguous segments of such reflectors forming a single stepped reflector;

Figure 2 is a diagrammatic view illustrating thedistribution of light from a long light source and two sets of rectilinear elliptical reflectorsV of the type shown in Figure l, placed on opposite sides of a vertical axis; Figure 3 is a' view illustrating the illumination of a working area by an annular luminaire;

' Figure 4 shows a photometric curve of an annular luminaire and an `illumination intensity curve on a working area at a distance; A

Figure 5 is a diagram illustrating reflector action with variousl locations of conjugate foci;

Figure 6 is a vertical cross sectional view through an annular luminaire such as employed in obtaining the curves of Flguret; l y

Figure '7 is an inverted plan view of the luminaire of Figure 6 with parts in section on the line 1-1 to show interior construction; and

Figures's to l0 illustrate modified forms of construction.

In Figure 1 the light center as well as one oi!v the foci of afseries. of ellipses is indicated by the latter F. The horizontal line'v I0 extendingl through this focus and the oblique line Il at an of approximately 60 to the horizontal -represent the limiting rays to the left of .a ver tical axis V-V which, it is contemplated, are to be intercepted by the reflector tothe left of' this distribution which will cover an .distribution oflight vertical axis and reflected downwardly through the conjugate focus F'. of the major and minor axes I2 and IZa as indicated. The lengths of these axes and the eccentricities ofthe ellipses will vary. For purposes of illustration the conjugate focus F is located so that the highest reflected ray from the outer edge I2.' of the reflector form is at an angle of 30 with the vertical, and furthermore F' is offset from line V-V a distance o f about 65% of the distance from F to I2.

With the foci F and F at assumed positions an indefinite number of ellipses may be drawn which intersect the lines I and II and in each case the reflector profile conforming to the elliptical contour between linesV III and II will intercept the same amount of light. -In the drawing a series of elliptical arcs are drawn. The largest starting at I 2' and having the greatestl eccentricity is lettered A. The smaller and less eccentric arcsl are lettered B, C and D. It is obvious that more or less than four ellipses may be employed and at an entirely diierent spacing. While a reflector form made according to any- .one of'these ellipses Will concentrate all the resmaller angle indicated at=B andit wouldfall y on the portion of the working plane WP between bb and bb. Similarly the reflectors C and D would concentrate the light in the regions indicated .by the angles C and D', respectively, and the light would fall on :the working plane between ccfand cc and dd and dd, respectively. The larger reflector A will, it is apparent, give a area greatly different from the area which can be reachedby light reflected by reflector D. In each ase the This fixes the location taken-out of `ellipses B and C, produce narrow 'light beams indicated at b and c'. It will be noted from the drawing that the reflector a produces a beam a' light, and that the reflector d produces a much more convergent beam d cident on it and thus condenses thelumen output in this zone.

By breaking up the reflector form into the four subordinate elliptical reflectors with intermediate inactive regions e, f and g, four zones of illumination a', b', c' and d', and three intermediate theoretically unlighted zones e', f', and g' are produced. The divergence to the left of the vertical v v through the focus F"availab1efin the smaller ellipse D is preserved and at the same time the divergence to the right of the vertical v-v by the larger ellipse A is preserved so that the overall divergence of the output of light from the stepped reflector is much greater than available with any single reflector of elliptical contour and the same foci and major axis. 'I'he zones e', f' and g' are indicated by light cross hatching in Figure 1 between the lighted zones d and c', c' and b', and b and a', They are brought about by reason of the fact that no specularly reflected light from the point source is emitted downwardly in the angles e', f', y' of Figure 1.

The inactive surface f is drectly above the conjugate focus F and hence no specularly reflected light is emitted vertically downward. If there were an active elliptical surface directly above the conjugate focus F it would project light rays parallel with the axis and tending to produce a region of excessive brightness near the center beam projected by the single reflector has a narrow distribution of light with non-uniform in- ,tensity throughoutthe width of the beam and tendsl to concentrate the light into a brightv spot when itfalls on the working plane. If therefore any vsingle reflector form were used such as A, B', C or D, one would obtain an entirely different on theworking plane. Figure 1 illustrates the' effect of 'employing a narrow segment only of each of the ellipses A, B, C and D and arranging 'these segments as indicated at a, b, c, ,d2 so that they occupy angularly contiguous zones about focus F and therefore will in the aggregate intercept the same amount of light as anyone of the wider angled elliptical segments A, B, C or D. The angles I selected in the drawings are arbitrary. In actual -design the contour of the stepped reflector will be such as to give the best distribution from the source to be used. The segment a of the ellipse A sends a beam of light indicated at-a', whose extreme ray below the conjugate focus -has the same inclination to the right of the4 vertical as did the corresponding light ray from the reflector A. The small reflector d produces a beam of light d" whose extreme ray below F has the same.. inclination to the left of the vertical as did the corresponding ray produced by the reilector D. Thev small elliptical reflectors b and c.

of 'the working area.

It will bevnoted from of the conjugate focus F is such that the divergence of light on each'side of the vertical v-v is approximately the same. A shift of the focus F to the right or to the left with corresponding change in the reflector contour will disturb thisapproximate .balance and build up the amount of light diverging to one side of the `vertical at the expense of light diverging to the other side lof the vertical.

The above discussion is based upon light rays from a point source and4 perfectvspecular reflection with reflectors perpendicular to the plane of the paper. In practice the light source instead of. being a point at F maybe on -opposite sides of F, as indicated at I3 and I4, and rays such as I5., I6, I 1 and I8 may converge on the reflector and be reflected as indicated at I5', I6', I1' and I8, .respectively, but generally toward F. In practice the reflector is not a perfect specular reflector and the glass used in the incandescent lamp bulb may be frosted. All vthis will act to causedivergence of the direct light rays greater than the theoretical into the intermediate or' theoretically dark zones.

- Where downwardly emitted light from the source is reflected upwardly by a cylindrical reflector I9 concentric with the focus F, there will be further divergence of the light rays on account of the eccentric position of the filament. As a result the intensity of illumination on a working plane with a rectilinear source and reflector both perpendicular to the plane of the paper may partake of the character illustrated by thecurve 20. 'I'he high intensity in the left portion of the curve is `brought about by the relatively large widthof the than the light rays inrespectively.

Figure 1 vthat the position and spread the light over `plane remote enough spreading action of zone d and the concentrating action of the correspondingV portion of the reflector.

Figure 2 illustrates the light output wheres. similar reflecting system has been placed on the i, opposite side of the vertical axis V-V .to distribute light from a conjugate focus F" to the right of the vertical axis V-V. The distribution. of light from the two conjugate foci F and F" on the working plane WP'is illustrated in Figure 2 and the same reference letters are employed as inFigure l1 to represent the distribu-l tion of light from focus F. The distribution of light from focus F.' is indicated by small letters with double primes and the distribution over the .working plane between aa' and dd insteadIof 4intensity of illumination to be had on a working to have allowed the two,

beams to mix. With this arrangement of rectilinear source and reiiectors it is possible to seillumination over a central area and a higher illumination on each side of the central area. This type of distribution is typically what one would use to build up higher intensities on opposite sides of 'an aisle; By properly selecting the angular Aextent of the refleeting zones, the divergences of the beams produced, the location of the conjugate foci, and the mounting height above the working plane it is possible to secure various distributions of light over the working plane which have low intensity in the center area and higher intensities in side areas.

Where the reilectorc cure a reasonably even ntour of Figure 1 is used in an annular reflector withan ordinary incandescent lamp the zones illustrated in Figure 2 may be deemed to be revolving about the vertical axis V-V. 'Ihis is illustrated in Figure 3, where the lines are drawn from the foci F' and F" the same as displaced from the center and therefore eccentric with respect to the center of `a spherical reilector. With the bowl silvered lamp ter and the reflected rays are therefore further scattered. This departure of the light rays from the ideal of the drawing will cause additional divergence of the light beams.

'Instead of the boundaries of elliptical areas being rectilinear as contemplated in Figure2, they are annular, and the lumen output from a source intercepted by an annular zone of unit angular width is a function of the angular position of the zone relative to the horizontal; for example, the lumen factor for a zone in the region of reflector a (which is in the95" zone above nadir) is 1.090, for the outer part of reflector d (which is in the 125 zone above nadir) is .897, and for the'inner'part of reflector d (which is in the 155 zone above nadir) is .463. As a` result of the variation of .lumen output ofthe source in theV vertical angular region underconsideration, the concentrating action of the inner reflector d, the the outer reflector a, the

variation in area. of annular regions on the working plane of equal'width, the overlapping of the beams and the scattering of light arising from diffuse reflection, diffusev transmission, sizeof light source and eccentricity of the spherical, or

- nearly spherical reector, the resultant illumination onthe working plane may be very even.

the reecting surface is ordinarily not concentric about the light cen- ,Y

from the vertical V-V to the point k25.

This evenness i the curve 2| in Figure 3, the spread being about 30 each side of the vertical. A i

Figure 4 shows the photometric curve of an annular luminaire with a stepped elliptical reiiector and a 150 watt bowl-silvered lamp. The

lamp output is illustrated at 22 and the luminaire output at 23. Thecurve 24 shows the intensity of illumination on a working area 10 feet below the luminaire.

In Figure 5 it is assumed that the light source is at F and that a series of reectors of elliptical contour, with one focus at F extend from the point25 on the horizontal plane through F upwardly toward zenith. The vertical lines marked 50%, 60%, l70% and 80% show the loci of conjugate focal offsets of the -namedpercentage sloping lines 26, 21 and 28 marked 45 max.

above nadir," 30 max. above nadir and 20 max. above nadir, respectively illustrate reflected rays at these angles from thepoint 25. vThese sloping and vertical lines are for purposes of ilv lustration. At whatever percentage oiset is selected and angle of maximum above nadir selected a point may be located where the lines intersect which forms a conjugate focus for an ellipse through thepoint 25, and for a series of other smaller elliptical arcs similar to those illustrated at b, c and d1 in Figure 1.

T-o illustrate the discussion the limiting elliptical arcs have been drawn using conjugate foci corresponding with the 45 maximum` and the in Figure 2. The lament isnec'essarily l to have the light cross below the light source each side of the vertical to each side of the and 50% oisets, and from the 20 maximum' and the 80% and 50% oilsets. The area bounded by these ellipticalzarcs is indicated by slanted cross hatching. All other ellipses frompoint 25 and having their conjugate foci within the region under discussion will fall within the cross hatched area,and it is obvious that when a stepped reiiector is used with the corresponding kconjugate focus its steps will be below the corresponding elliptical arc which goes through the cross hatched area.v As an indenite number of such stepped elliptical contours might be drawn they are omitted for clearness.

vAsit isintended to use a companion ellipse on the opposite side of the vertical V--V vand and mix so as to spread over the working area to the same extent on each side of the vertical, .i it is desirable as the next assumption in designing the reflector to assume a maximum angle' above nadir of the downwardly slanting rays from the outer margin of the reilector which equals ythe maximum angle above nadir of vthe downwardly 'slanting rays from the region of the reectonnear zenith.

In Figure 5 a number of dash lines slanting V upwardlyand'to the right appear, and to these thereference character 29 is generally applied. These lines arey drawn through selected intersections `of thesloping lines 26, 21 and 28 and the percentage .offset lines, each such dashline being at the same angle to the vertical as the corresponding, maximum angle of the ray reected from thepoint 25. It will be seen that these lines generally go through a region near zenith and thatthe reflector may be terminated at such a point near the zenith so that .in typical cases the bisector of the extreme reflected ravs may be vertical.V It will also be apparent from the /drawings that it is possible to design elliptical reflectors giving adistribution offrom 20 The vertical and maintain the conjugate focus at a reasonable distance below the light source.

In the actual design of luminaires employing the elliptical reflector with or without steps it will, of c'ourse, be understood that proper consideration must be given the permissible diameter and depth of the unit, the necessary cut oil and screening angles, and the obstruction caused by the upwardly acting reflector, where one lis used, or. the obstruction caused by the opaque light source where such a source is employed.

A structural embodiment of an annular luminaire is shown in Figures 6 and 7. Apendent lamp bulb 30 is carried by the socket 3| connected to asuitable outlet box 32. 'I'he outlet box 32 carries a suitable cone shapedmember 33 which is secured in any suitable manner to asheet metal reflector 34 having an aperture 42 to accommodate the lamp bulb. This reflector is a surface of revolution about the vertical axis through the source and has a plurality ofzones 34a, 34h, 34e and 34d of elliptical contour With one focus F at the light source and conjugate foci indicated at F and F" and disposed in a circle indicatedI by the dot and dasharc 35, Figure 7. 'Ihe intermediate orinactive areas 34e, 34f, and 34g are sumciently steep to avoid intercepting direct light either on their surfaces or on the llets which connect them with the active surfaces. The luminaire is provided with an outercylindrical screen 35 extending downwardly from the periphery of the reflector and carrying aflat apertured plate 31 at approximately the level of the foci F and F". As here shown the lamp bulb is received in aspherical reflector 38. This reflector, as well as an innercylindrical screen 39 and aflatscreening disk 40 are supported from the upper reflector 34 f by clips 4I which pass up through the central opening 42 of the upper reflector. The luminaire can be conveniently recessed in aceiling 43 as indicated. `The aperture formed between thedisk 40 and theplate 31 is sufficiently large to provide a window to allow substantially all the desirable light from the reector to escape in the controlled directions. The light may therefore pass downwardly without passing through a dust collecting medium. 'Ihe disk and plate together with thecylindrical screens 36 and 39 will completely screen the light source and the reector 34 from the eye of an observer outside the region where the intense rays are being transmitted. The inside surface of the 36 and the outside surface of thescreen 39 may be coated any desired colo'r and this will be brought out by the spilled light intercepted by these elements.

In Figure 8 the outlet box, reflector and support forthe same are shown as in Figure 6 and the same reference characters applied. Here `thereflector 34 andsupport 33 are recessed in the ceiling and the screening means is in the form of a translucent bowl having outer diffusing side walls 5| and is held up by screws 52. It also has inner diffusingside walls 53 which extend up near the bulb at substantially the level of the light source so as to facilitate the removal of a bowl silvered lamp 30'. An annular region 54forms the' window for transmission of reflected rays. This window may be clear crystal glass where the diffuser is of glass, or one may employ openings as illustrated at 55 in Figure 9 where a plastic diffuser is used. be flat as indicatedv at 56.

`Figure 10 illustrates theuse of a long light Screen The center may common focal point at distribution to supplement that from the upper y reflector. It also acts as a screen when the luminaire is viewed from the side.

Since it is obvious that the invention may bc embodied in other forms and constructions within the scope of the claims, we Wish it to be understood that the particular forms shown are but a few of these forms, and various modifications and changes being possible, we do not otherwise limit ourselves in any way with respect thereto.

What is claimed is:

1. A luminaire comprising ,a `light source, af l downwardly acting specular reflector symmetrical on opposite sides of a central vertical axis through the source and accepting substantially all the light emitted by the source in an axial plane and above a horizontal plane near the level of the source, the reflector being composed of angularly contiguous reflectingzones of variant light accepting angles and of elliptical profile in said axial plane vand separated by inactive zones, the said reflecting zones having a the center of the light source and coincident conjugate focal points in said axial plane and uniformly displaced on opposite sides of `said central vertical axis, the axes of the ellipses in which zones are formed being shorter as the zones approach the central axis of the luminaire for the purposes described, each of theA focal points being so spaced below the horizontal plane through the source' that horizontal incident rays low the horizontal than 2. A luminaire comprising a light source. an upwardly converging reflector form extending from two opposite points substantially equidistant from the source and substantially in the horizontal plane through the light source, the reflector form being specular and of elliptical contour with one focus at the light source and with coincident conjugate foci forming virtual light sources andfspaced substantially below said horizontal plane a distance greater than 50% of the distance from the source to the corresponding opposite points from which the reflector starts and substantially less than the entire distance, and wherein the reflector form has contiguous reflecting zonesof variant light acceptgreater than 45 and less ing angles and intermediate inactive zones for the purposes specified, and outer screening means extending lfrom the conjugate focal Vregion tothe outside of the reflector form and inner screening means extending from the conjugate focal region to the said horizontal plane whereby the reflector form and source are screened at angles outside the spread of the controlled specularly reflected rays.

3. A luminaire for illuminating to a substantially uniform intensity of illumination a predetermined horizontal circular area vsymmetrically below a vertical axis through the luminaire, comprisingan axially disposed light source above said area, a spherical reector below the source, an annular stepped specular reflector disposed above and on opposite sides of said source, said reflector having a plurality of angularly contiguous areas of elliptical contour with one focus at the light source and the conjugate foci coinare reflected at angles be- A 2,297,124 i cident and annularly disposed with respect to substantially .all the upwardly emitted light and said vertical axis, the elliptical areas adjacent redirect it so as to`converge and pass vthrough the source having the shorter axes, whereby a narrow annular region disposed below the zones of reflected light converge at said consource and of a' diameter such that none of the jugate foci and diverge therefrom with an over- 5 reflected rays cross the `axis of the iixture until all divergence suicient to cover said area to be they have proceeded a substantial distance belighted, and the zones of reflected light are low said annular region, a spherical reflector beseparated by zones of comparative darkness, low thesource and supported from the upper some of the zones of illumination produced on reiiector, an outer screen extending from the said area by the reflector to one side of the periphery of the annular reiiector to the outside vertical axis substantially coinciding with the of said annular region, arid an inner screen exzones of said area which would be comparatively tending from the inside of said annular 'region to dark if receiving light only from the opposite the spherical reflector so that' no glare from the i side of the reflector, and screens extending from light source proper nor glaring specular reflecadjacent the region containing said conjugate tion thereof will be visible when the unit is viewed foci to the outer peripheries of the mentioned from points beyond the controlled light beam.-

reflectors. 6. A luminaire as claimed inclaim 1, having 4. A lighting unit comprising a light source, `directly above each conjugate focal point an ina downwardly acting specular reflector above the active zonenso that no light originating at the source adapted to intercept substantially all the common focal point is reflected vertically down- `upward1y emitted light-and redirect it so as to wardly. converge and pass through narrow regions dis- 7. A luminaire as claimed inclaim 1, wherein posed below the source and so oifset from the the zones of reflected light converging at said vertical plane through the source that none of conjugate focal points and diverging therefrom the reiiected rays cross the axis of the fixture g5 are separated by zones of comparative darkness until they have proceeded a substantial distance and the zones of illumination produced on a below said regions of convergence, a concentric working area by the reflector at one side of the reflector below the source to reflect light into vertical axis substantially coincides with the said upper reflector, outer screening means ex. zones of said area which would be comparatively tending from the mouth of the upper reiiector dark if receiving light only from the'opposite side to the outside of said regions, and inner screenof the reector.

ing means extending from the inside of said re- 8. A luminaire asclaimedin claim 1, wherein gions to the concentric reflector so that no glare the light source is a. point source, the reflector from the light source proper nor glaring specular is annular and locus of the conjugate foci is a reflection thereof will be visible when the unit circle whose center is in the vertical axis. is viewed from points beyond the controlled light 9. A luminaire as claimed inclaim 1, wherein am. the light source is elongated, the reflector is .5. A lighting unit comprising a downwardly rectilinear and the loci of the conjugate foci are opening iixedly supported lamp socket, a lamp parallel. bulb therein, an upper, fixedly supported, an- 40 VICTOR. GEIST ANDERSON.

nular, downwardly acting reector apertured t0 EDWARD RAMBUSCH. accommodate the bulb and adapted tointercept 4

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