US2198096A - Portable lamp - Google Patents

Description

April 23, 1940.

A. J. SWEET 2,198,096

PORTABLE LAMP Filed July 24, 1936 2 Sheets-Sheet 1 INVENTOR fqh wegf' e- M ATTORNEY April 23; 1940.

A.. J. SWEET 2,198,096

PQR'I'ABLE LAMP Filedqfihly 24,1956

INVENTOR w fSu'eef BYZ ATTORNEY 2 Sheets-Sheet 2 Patented Apr. 23, 1940 UNITED- STATES PATENT OFFlCE PORTABLE LAMP Arthur J. Sweet, New York, N. Y. Application July 24, 1936, Serial No. 92,299

'7 Claims.

This invention relates to illumination, and more especially to light-controlling devices. In its more specific aspect the invention is directed to portable electric table and floor lamps having means for controlling the illumination of predetermined areas.

The central and essential feature of my invention consists of a specular or substantially-specular reflector which directs light on the work, used in conjunction with a second reflector, preferably specular, but not necessarily so, which directs light to the ceiling. The two reflectors are preferably so joined mechanically as to consti tute a single device. By varying the proportions of the two reflectors, it is possible to vary within wide limits the relative amount of light directed, respectively, to the work and to the ceiling.

vIt is an essential and definitive characteristic of my invention thatthe reflector which directs light to the work be of such contour and position with respect to the primary light source as to direct its reflected light chiefly to the 45- 60 zone (nadir=, zenith-180), or. to a sector of this zone, the intensity of the reflected light increasing as the zonal angle increases, being 2 to times as great at the upper limit as it is at the lower limit. r

It is to be understood that permissible variations in design may involve a variation of as much as 5, plus or minus, in the above zonal limits. Indeed, in the case of the floor lamp, such permissible variation in design may involve a variation as great as minus in the zonal limitsl Y 'Ihe'more specific nature of my invention will be readily apparent from the following description and drawings, wherein:

Figure 1 is a top plan view of a portable desk or table lamp embodying my invention.

Figure 2 is a cross-sectional view of the portable lamp illustrated in Figure 1.

Figure 3 is a top plane view of the floor lamp shown in Figure 4.

Figure {l is a cross-sectional view of a floor lamp embodying my invention and is a modification of Figures 1 and 2.

, Companion Figures 1 and 2 show a portable desk or table lamp whose base Ill supports a pedestal H. Mounted on said pedestal is an electric incandescent lamp 12 having a coiled filament or other type of light source marked by the character X. Surrounding said lamp !2 in all directions in which, under normal conditions of use,"a human eye might be located is an ordinary translucent or opaque shade l3 supported by arms l5. The foregoing lamp parts are derived from the prior state of the art, and no element of invention is claimed in connection therewith other than in their association with the items below described.

According to my'invention the bottom of the I shade should'lie above, but preferably only very slightly above, the line a, drawn from the center of the light source to the farthest work-posi-- tion for which the lamp is designed. The top of the shade will preferably lie on a line drawn through the light source at an angle of 135 with the nadir, or roughly approximate thereto. The diameter of the shade at the bottom should be as great as considerations of appearance permit. Other features of shade design are chiefly determined by considerations of appearance.

Within said shade l 3 are located two reflectors l6 and I1 which may be joined to constitute mechanically a single composite reflector.

Reflector l6 may be made of any mechanically suitable material of good reflecting quality. It is preferably'made with a specularly-reflecting interior surface and a diffusely-reflecting exterior surface. Among suitable materials are Alzak aluminum and chrome-plated steel, copper or brass, having polished inner surface and depolished or painted outer surface. Reflector I6 may also be made of white glass or of a white molded plastic, or of crystal glass with silvered exterior surface backed by acoat of white paint.

The lower edge of reflector it, except as cut away to accommodate reflector ll, lies on or very to the top of the shade.

The contour of reflector l6 and the direction in which the light isv reflected therefrom may vary considerably without'materially afiecting the satisfactory functioning of my invention, but it is preferable that the contour thereof and the consequent direction of reflected light be such that the combined'upward light distribution of lamp and reflector afford an approximation to uniform illumination of a horizontal ceiling throughout the 150-.180. zone. The satisfactory functioning of my invention will, however, be maintained by a reflector which directs the light to some portion of the l-180 zone.

The lower edge of reflector H lies on or very slightly above line a (Fig. 2), drawn from the light source to the farthest work-position for which the lamp is designed. The upper edge of reflector l1 lies at such angle with the nadir as will provide the desired relationship between the illumination on the work and the general illumination of the interior as produced by the upward-directed light. On general, this angle will be not less than 90 nor more than 135. The

- contour of reflector l! is such as to provide, in

combination with direct, non-intercepted light from the source, an illumination which does not materially decrease and preferably increases as the horizontal distance from the vertical line through the light source increases, throughout the range of work positions for which the lamp is designed. In the case of a desk or table lamp having a light source l8? above the horizontal plane of the work, the preferred height for this type of lamp, the above work-range corresponds to a zonal range of 496l. In the case of a floor lamp having a light source 24 above the horizontal plane of the work, the preferred height for this type of lamp, the above work-range corresponds to a zonal range of 45-58.

The contour of reflector I1 is determined as follows:

The mounting height above the horizontal plane of the work having first been decided upon, the exact zonal range corresponding to the range of work positions for which the lamp is to be designed is computed. The amount of light required to produce the desired average intensity of illumination is next computed. This is ob-' ta-ined by multiplying the desired average intensity expressed in foot-candles by the area of the ring formed in the horizontal plane of the work by the limits of the zonal .range of the work, this area being measured in square feet. The amount of light so obtained is hereinafter designated as required work .lumens.

The amount of light emitted by the light source within the zonal range of the work, when operated without accessory light-controlling equipment, is next determined by photometric test and .computations therefrom. This light is hereinafter referred to as "light source .lumens on work. The light source lumens on work are subtracted from the required work lumens to give the "required reflected .lumens on work. The required reflected lumens on work are divided by a constant representing the reflecting efficiency of the particular .material employed for reflector 11 to give the required incident lumens on reflector.

The lower edge of reflector l1 lies at the upper limit of the zonal range of the work. The upper edge must lie at such angle as to intercept .an amount of light equal to the required incident lumens on reflector. Since photometric test on the unequipped light source and computations therefrom will disclose the amount of light emitted by the sourcein any zone, the angle at which the upper edge of the reflector must lie to intercept the required amount of light may be determined by such computations.

If the upper edge of reflector i1 is found to lie at a higher angle than it is desirable to adopt for the upper edge of reflector 15, either the average intensity of illumination to be provided on the work must be reduced or a larger lightsource employed. Under either alternative, the computations above described are revised to apply to the new set of conditions.

The zonal range of the work is next divided into any desired number of sub-zones, the number depending upon the desired exactness of design. Typically, 4 sub-zones will be sufficient. The relative quantity of light required to produce the same intensity of illumination in each sub zone is next computed, being directly proportional to the difference between the squares of the tangents of the angles defining the respective sub-zone limits. The relative quantity in each sub-zone being known, it can be expressed as a percentage of the total quantity in all sub-zones. Apportioning the required work lumens in accordance with these percentages, the theoretical sub-zone lumens are obtained for each subzone. For each sub-zone, the light source lumens emitted within that sub-zone are subtracted from the theoretical sub-zone lumens to give the theoretical reflected sub-zone lumens.

Starting now at an angular distance from the nadir equal to the upper limit of the zonal range of work positions, the contour of reflector I1 is so inclined as to deliver its reflected light in the sub-zone farthest from the nadir. This involves a contour which starts at its bottom edge almost vertically and inclines more and more towards the light source as it extends upwards. The contour at any point is perpendicular to the bisector of the angle between the incident and the reflected light.

Proceeding upward by small increments, the contour is extended until the intercepted lumens, multiplied by the reflection constant above referred to, equal or exceed the theoretical reflected sub-zone lumens for the sub-zone farthest from the nadir. Then the contour is so inclined as to reflect the intercepted light into the next adjacent sub-zone, and is continued upward by small increments until the intercepted lumens, multiplied by the reflection constant above referred to, equal or exceed the theoretical reflected sub-zone lumens for the subzone next to that farthest from the nadir. So proceeding, sub-zone by sub-zone, the contour is extended upward until the limiting angle for the top of reflector l! is reached. The so-produced reflector ll extends upwardly inward towards the vertical through the center .of light source X.

Reflector I! is a surface of revolution about a vertical axis through the light source. The revolution defining the surface may be a complete revolution of 360, or may be any part thereof. In the case of lamps designed for use in the home, reflector I 1 will preferably be a surface of revolution throughout 360. In the case of lamps designed for use of a single person in oflice or study, reflector I I will preferably be a surface of revolution through 90. The composite unit consisting of reflectors l6 and I! may be supported by a lip on reflector l6 bearing against the upper edge of the shade or by arms secured to the pedestal I'l.

Screen 26, Figure 2, may be made of any mechanically suitable material which can be so formed or treated as to transmit only a prede-' termined portion of the incident light and to diffuse the light so transmitted. Proper amount of transmission anddiffusion will be determined by the requirements that no part of the under surface of the screen shall have a brightness exceeding 5 candles per square inch and that the average brightness shall not exceed 2 candles per square inch. Brightness values half as great as these limiting values are preferable. The screen may be made of white glass or of white molded plastic, the optical density of the material being such as .to provide, in conjunction with the thickness employed, the proper amount of light transmission and diffusion.

Through the center of the light source draw a line, the inner limit of the zonal range of work positions for which the lamp is designed. Through the bottom edge of reflector I! draw a line parallel with the outer limit of the zonal range of work positions. The point where these two lines intersect, if revolved around a vertical axis passing through the light source, establishes the theoretical position of the circumference of screen 20. This position, however, involves either an undesirable projection of the screen below the shade or a shade of too large bottom diameter for pleasing appearance. The actual position of the circumference of screen 20 is therefore a compromise, lying at least 45 from the nadir and on or slightly above the line drawn through the bottom of reflector l1 parallel with the outer limit of the zonal range of work positions. The screen is designed to'intercept all light emitted by the source at a lesser angle than that subtended by the circumference.

Substantially all of the light reflected by the designed reflector I"! is directed in paths extending downwardly towards and beyond the vertical through the center of the light source X and above the pedestal ll and above the screen 20 and between the outer edge of the screen 20 and the lower edge of the shade l3 to the workarea spaced a material distance from said vertical to supplement appreciably that portion of the direct light from source X which travels above the support and between the outer edge of the screen 20 and the lower edge of the shade l3 to said work area as shown in Figure 1.

Within the circumference the screen may be a flat disk or may be dished as shown in Figure 2. When the shade I3 is translucent, screen 20 serves a secondary purpose of reflecting light to the inside of the shade, which light will in part pass through the shade and improve its appearance. This purpose is better served by theinverted dished form of screen shown in Figure 2.

The screen may be of substantially uniform thickness, ortapered as shown in Figure 2.

The screen may be made in part of opaque material provided approximately one-third or more of the area of the screen is translucent.

Where no specular surfaces are apt to lie in the visual field surrounding the work, as is typically the case with the floor lamp, screen 20 may be omitted as apart of my invention without materially impairing the utility thereof. Where, however, a translucent shade is employed and screen 20 is omitted, I provide another aspect of my invention to light up the translucent shade. This aspect consists in providing transparent interruptions in the reflecting surfaces of both reflector l6 and reflector l1, through which interruptions light is transmitted to the inner surface of the shade. By properly proportioning the size and spacing of these interruptions, their images on the inner surface of the shade are made so to overlap as to produce a substantially uniform illumination of this surface, the images blending and substantially or entirely disappearing. The size and'spacing of the interruptions necessary to produce this eifect depend upon the projected dimensions of the light source, the distance of the light source from the interruption and the distance of the interruption from the surface on which its image is cast.

Companion Figures 3 and 4 show my invention as typically applied to a floor lamp. In these figures, a base 30 supports a pedestal 3| which in turn supports an incandescent lamp 32. Partially surrounding said lamp is the shade 34 supported by the arms 33. The description heretofore given of the similarly-named elements of companion Figures 1 and 2 apply equally to these elements.

Within said shade 34 are located two reflectors, 3'! and 3B, which may be joined to constitute mechanically a'single composite reflector. The de-- scription heretofore given for reflector I'B of Figures 1 and 2 applies equally to reflector 31. The description heretofore given for reflector [1 applies equally to reflector 38. The difierences in form ofthe two combinations result chiefly from the fact that reflector 38 is a surface of revolution through 360 while reflector H is a surface of revolution through 90. In other respects'the principles of design are the same.

Reflectors 3'! and 38 are provided with perforations 4!] whose purpose and character has herein above been fully set forth.

The composite unit consisting of reflectors 31 and 33 may be supported by an inner web'resting on lamp 32, or by arms carried by pedestal 3|.

Although my invention has been described in detail it is not to be limited by the exact construction shown in the drawings except as specifled in' the claims.

What is claimed is:

l. A portable lamp comprising a support, a light source carried by said support, a shade whose lower edge is approximately in a line drawn between the center of said light source and the farthest work position for which the lamp is designed, a brightness screen lying approximately in the plane of the lower edge of said shade, the outside periphery of said screen lying, with respect to the center of the light source, at approximately 45 from thenadir and having reflecting, absorbing and diffusing characteristics such that the underside of the screen nowhere shows a brightness exceeding 5 candles per square inch, and a specular reflector for reflecting a portion of the light from said source to a horizontal work area'extending from approximately 45" from the nadir to approximately 60 from the nadir, the contour of said reflector and its position relative to said light source and to said brightness screen being such that said portion of light reflected by said reflector passes chiefly above said screen and chiefly below said shade to said work area to produce thereon an illumination which is substantially as great at portions of said work area remote from the vertical through the light center as it is at portions of said work area closer to said vertical.

2. A portable lamp comprising a source of light, a pedestal, a shade, said source of light carried by said pedestal, encircled by said shade and emitting a portion of its direct light below the lower edge of said shade to a horizontal work area whose inner limit is spaced from the vertical through the center of said source of light a distance approximating the distance from the plane of said work area to the center of said source of light, and a specular reflector located between said'shade and said source of light and intercepting light emitted by said source of light in the zone lying between approximately 60 and at least 90 from the nadir, said reflector extending upwardly inward towards said vertical and directing substantially all of the light reflected by it downwardly towards and beyond saidvertical and above said pedestal and below said shade to said work area, said pedestal located substantially entirely below said path of reflected light, the lower edge of said shade being approximately 60 from the nadir and located in a plane materially below said lower limit of said reflector.

3. A portable lamp comprising a support, a source of light, a shade, a screen and a specular reflector, said screen located below said source of light and limiting the degree of brightness of said source as viewed within an appreciable angle from the nadir, said source of light encircled by said shade, carried by said support and emitting a portion of its light downwardly between the outer edge of said screen and the lower edge of said shade to a horizontal work area spaced a material distance from said support, said specular reflector located between said shade and said source of light and intercepting light emitted by said source in the zone lying between approximately 60 from the nadir and at least 90 from the nadir, the outer periphery of said screen disposed at a greater distance from the vertical through the center of said source of light than the distance from said vertical to said lower limit of said reflector, said screen located below and vertically spaced from the plane of said lower limit of said reflector, said shade horizontally spaced from the outer periphery of said screen, said lower limit of said reflector located above and vertically spaced from the plane of the lower edge of said shade, said reflector extending upwardly inward towards said vertical and reflecting the light intercepted thereby chiefly in paths extending from said reflector downwardly towards and beyond said vertical to said work area and between the outer limit of said screen and the lower limit of said shade, said support and screen located substantially entirely outside of said path of reflected light.

4. A portable lamp comprising a support, a source of light carried thereby, a shade for said source of light, a specular reflector located be tween said shade and source of light, the lower edge of said reflector being approximately 60 from the nadir and the upper edge of said reflector being at least 90 from the nadir, a brightness screen located below said source of light and intercepting the light from said source in the zone lying between and 45 from the nadir, the optical density of said screen being such that some light passes therethrough and the brightness of the lower surface thereof is less than five candles per square inch, said screen lying approximately in the plane of the lower edge of said shade, the lower edge of said shade being approximately 60 from the nadir and located below the lower edge of said reflector, said reflector extending upwardly inward towards the vertical through the center of said source of light and directing substantially all of the source light reflected by it downwardly towards and beyond said vertical and above said screen and below said shade to a horizontal work area, said support located substantially entirely outside of the path of said reflected light.

5. A portable lamp comprising a source of light, a pedestal, a shade, said source of light carried by said pedestal, encircled by said shade and emitting a portion of its direct light below the lower edge of said shade to a horizontal work area whose inner limit is spaced from the vertical through the center of said source of light a distance approximating the distance from the plane of said work area to the center of said source of light, and a specular reflector located between said shade and said source of light and intercepting light emitted by said source of light in the zone lying between approximately 60 and at least 90 from the nadir, said reflector extending from approximately 60 from the nadir to at least 90 from the nadir upwardly inward towards said vertical and directing substantially all of the light reflected by it downwardly towards and beyond said vertical and above said pedestal and below said shade to said work area, said pedestal located substantially entirely below said path of reflected light, the lower edge of said shade being approximately 60 from the nadir and located in a plane materially below said lower limit of said reflector.

6. A portable lamp comprising a support, a

source of light carried thereby, a shade for said source of light, a specular reflector located between said shade and source of light, the lower edge of said reflector being approximately 60 from the nadir and the upper edge of said reflector being at least 90 from the nadir, a brightness screen located below said source of light and intercepting the light from said source in the zone lying between 0 and 45 from the nadir, the outer limit of said screen being approximately 45 from the nadir, the optical density of said screen being such that some light passes therethrough and the brightness of the lower surface thereof is less than five candles per square inch, the outer edge of said screen disposed adjacent the plane of the lower edge of said shade, the lower edge of said shade being approximately 60 from the nadir and located below the lower edge of said reflector, said reflector extending upwardly inward towards the vertical through the center of said source of light and directing substantially all of the source light reflected by it downwardly towards and beyond said vertical and above said screen and below said shade to a horizontal work area, said support located substantially entirely outside of the path of said reflected light.

7. A portable lamp comprising a support, a light source carried by said support, a shade whose lower edge is approximately in a line drawn between the center of said source of light and the farthest work position for which the lamp is designed, a brightness screen below the upper portion of said shade and disposed adjacent/the plane of the lower edge of said shade, the outside periphery of said screen lying, with respect to the center of the light source, at approximately 45 from the nadir and having reflecting, absorbing and diffusing characteristics such that the under side of the screen nowhere shows a brightness exceeding 5 candles per square inch, and a specular reflector for reflecting a portion of the light from said source to a horizontal Work area extending from approximately 45 from the nadir to approximately 60 from the nadir, the contour of said reflector and its position relative to said light source and to said brightness screen being such that said portion of light reflected by said reflector passes chiefly above said screen and chiefly below said shade to said work area to produce thereon an illumination which is substantially as great at portions of said work area remote from the vertical through the light center as it is at portions of said work area closer to said vertical.

ARTHUR J. SWEET.

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