US1867502A - Light reflector - Google Patents

Description

: Jul 12, 1932.

K. A. EDSTROM LIGHT REFLECTOR Filed March 7. 1950 Patented July 12, 1932 UNITED STATES PATENT OFFICE Application filed March 7,

or filament shadows.

A further object is to provide a reflector which maybe positioned relatively close to the surface which it is desired to illuminate so that the beams will reach the surface with a maximum intensity. and but a minimum of space will be required.

- Other objects and advantages reside in the detail construction of the invention, which is designed for simplicity, economy, and efficiency. These will become more apparent from the following description.

In the following detailed description of the invention reference is had to the accomproved reflector illustrating the paths of typical light beams. This section is taken on the line 11, Fig. 2.

Fig. 2 is a plan view of the complete reflector.

Fig. 3 is a diagrammatic view illustrating the reflector positioned so as to illuminate a relatively high vertical surface such as the front of a building or the like.

Fig. 4 is a similar view illustrating the placement of the reflector for illuminating a relatively large horizontal surface such as the ground. 7 The invention comprises a primary reflecting surface 10 havin the contour of an ellipsoid. The foci of tfle ellipse are indicated at A and B. A secondary reflecting surface 11, also having an ellipsoidal contour, joins the reflectin surface 10 and projects outwardly there rom with its major axis in alignment with the major axis of the surface 11. The reflecting surface 11 em- 1930. Serial No. 433,932.

ploys the focus B of the surface 10 for one of its foci, the other being indicated at C. The two surfaces 10 and 11 are joined on a plane which substantially intersects the focus B. l 6 Substantially half of the surface 11 is cut away, preferably on a vertical plane intersecting the foci B and C, as indicated in Fig. 1. The amount cut away, however, varies with the purpose of the reflector. Should it be desired to illuminate a relative- 1y small area, less than half will be cut away. The reflecting surface 10 is provided with a supporting base 12 which adjustably carries a lamp receptacle l3 supportinga suit- 68 able lamp or light source 14. The receptacle 13 may be set in any desired position in the base 12 by means of a set screw 15 so as to bring the filament of the lamp 14 to the focal point or focus A. x

The'base 12 is simply illustrative of a type of base which may be provided. Other bases could be devised for special purposes or the light reflector might be enclosed in a suitable supporting housing (not shown) having a suitable lens. These are features within the skill of the ordinary user and form no part of the present invention which relates only to the reflecting surfaces.

In Fig. 1 typical light beams have been illustrated by; broken lines at 16, 17, 18, 19 and 22. It will be noted that owing to the ellipsoidal contour of the reflecting surface '10 all incident rays from the light source 14:-

are reflected to an intersection or focus at B. A portion of these rays, such as indicated at 16, pass through the focus B and outwardly through the open side of the reflector as indicated by the rays 17. Another portion of the rays as indicated at 18, pass through the focus B as indicated at 23, and strike the reflecting surface 11 from which they are reflected so as to again intersect each other at the focal point or focus C. After passing through the focus G they are projected outwardly through the open side of the reflector as indicated by the rays 19.

The rays 17 and 19 spread the light over .the entire area to one side of the reflector.

These rays are so interlaced and overlapped by being projected from two separate focal points that all filament shadows or other dark spots from one focal point are covered by llght rays from the other. 1

Additional coverage is obtained by incident rays from the focus A striking directly on the secondary reflector 11, and being pro- 'ected at a still different pro ection angle, as indicated by the dotted line 22. These rays 22 also assist in covering the imperfections in the other'two sets of overlapping rays (17 and 19) so that an absolutely uniform illumination is assured.

It would seem from the above that the entire source of reflected light was at the focus Experiments however, prove that both the foci B and C serve as additional light sources. At both theselatter foci a complete brilliant image of the filament or light source of the lam 14 appears. The image at B has but slight y less intensity than the originalat A and the image at G has but slightly less intensity than the image at B.

The brilliant image at B reprojects light back into the reflecting surface 10 as indicated by the arrow X. This reprojected light is refocused at A to intensify the original light source, thereby greatly intensifying the projected beams. A portion of this reprojected light will pass through the original light source and again strike the reflecting surface 10 and intensify the beams 16 and 18 so as to reintensify the brilliancy of the image at B. A portion of these intensified beams will project through the focal point B, intensifying the beams 17. Another portion will pass through the point B and intensify the beams 23 and the image at C be fore passing out to intensify the beams 19.

Th1s same phenomenon occurs with relation to the reintensified image at C, which is also a brilliant reproduction of the light source at A.. This brilliant image at C will reproject light backwardly against the reflectin surface 11, as indicated by the arrow This reprojected light will be refocused at B to further intensify the image at B and through it the original source at A.

In other words, all light beams before leaving the reflector must pass through the focal points B and C, where they create brilliant images to serve as original light sources. These brilliant images are themselves re-reflected to constantly build up the volume of projected light. It is not known exactly how much of the light is reflected from the images but experiments seemto indicate that the lumen intensity is increased approximatel 300% by reflection from the two images and C.

The fact that the images B and 0 do actually serves as original light sources can be readily demonstrated by positioning a small parabolic reflector between the foci B and C, with the focus C at its focal point. If

this is done a brilliant beam will be projectedfrom the inserted parabolic reflector although no direct beams from the lamp 14 can reach its reflecting surface. "The reflector has many uses, such as..illuminating the walls of buildings, signs,;etc., such as indicated at 20, Fig. 3. F or this purpose the reflector may be positioned a short distance. in front of the vertical surface which it is desired to illuminate. The beams will then be projected evenly over'the en-' tire surface. In Fig. 3, the reflector is positioned at the bottom of the surface '20. It could, of course, be hung downwardly from a bracket at the top of this surface with equal efliciency. I

For illuminating large floors or fields' such as indicated at 24, Fig.4., the reflector could be positioned upon a wall or post such as at 21. It would then uniformly spread the light from immediately belowthe reflector to an infinite distance beyond it.

When the light 14 is not lighted a double image of the filament of the light-can be seen at the focus B. If the secondary reflector 11 is removed one of these images disappears leaving but a single image of the filament.

This definitely indicates that the 'second 7 image at B is thrown back from the image at C, and appears to be positive proof that the image at B is intensified by return rays from the Image C.

While a specific form of the improvement has been described and illustrated herein, it is desired to be understood that the same may be varied, within the scope of the appended claims, without departing from thespirit of the invention.

Having thus described the invention, what is claimed and desired secured by Letters Patent is I 1. A light reflector comprising: an ellipsoidal reflector; means for supporting a light source at the rear focus, said reflecting surface being truncated adjacent the forward focus; a second ellipsoidal reflecting surface joining said first surface at said truncation, the rear focus of the latter coincidin with the forward focus of the primary re ecting surface, the forward focus of the latter being in alignment with the two foci of the primar surface, said secondary reflector com, prismg: substantially half of an ellipsoid positioned to one side of the major axis so as to leave the other half open to allow the rays from one side of the forward. focus bf the ward focus of the second reflector being in alignment with the two foci of the first rev flector, said sezo'nd reflector comprising: substantially hal of an ellipsoid positioned to one side of the major axis so as to leave the other half, oFen to allow the rays from one side of the orward focus of the second reflector to project outwardy, said second reflector extending forwardly of the forward focus thereof.

In testimony whereof I aflix my si ature.

mi, A. EDST OM.

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