US2096453A - Reflector for rectilinear light sources - Google Patents

Description

Oct. 19, 1937. 5 2,096,453

REFLECTOR FOR RECTILINEAR LIGHT SOURCES Filed June 27. 1934 INVENIOR. .Maurz'ce Exelmans.

WMAJ A TTORNEYI Patented Oct. 19, 1937 UNITED STATES PATENT OFFICE REFLECTOR FOR RECTILINEAR LIGHT SOURCES Maurice Exelmans, Paris, France,

liolophane Company, Inc.,

asslgnor to New York, N. Y., a

In France 7 Claims.

The present invention relates to reflectors for rectilinear light sources.

The divergence of light rays reflected from a point on a reflector is a function of the size of the light source. Where point, or substantially point, light sources are employed the divergence of the reflected light is comparatively small and may serve to improve the diffusion of the light without seriously impairing the control of the dominant light into the desired direction. Where long light sources are employed, divergence of the reflected light in longitudinal planes is substantial, depending upon the length of the light source and its distance from the point on the reflecting surface under consideration. The minimum angie of divergence in such longitudinal planes is obtained at a point where the normal to the reflecting surface intersects the center of the long light source. Long reflecting troughs such as ordinarily used with long light sources have been found unsatisfactory. especially when one desires to avoid spreading the light through wide angles longitudinal of the long lighting unit.

According to the present invention the reflector they may be made in molds capable of manufacture by ordinary machining operations.

Other and further objects of the invention will appear as the description proceeds.

The accompanying drawing shows, for purposes of illustrating the present invention, two of the many possible embodiments in which the invention may take form, it being understood that the drawing is illustrative of the invention rather than limiting the same. In the drawing:

Fig. 1 is a transverse sectional view through a prismatic cylindrical reflector in a plane perpendicular to the source showing the control of the rays in this perpendicular plane;

Fig. 2 is a longitudinal sectional view in a plane parallel to the source showing the control of the rays in this plane; and

Figs. 3 and 4 are sectional views in planes respectively perpendicular to and parallel to the source showing a'modifled form of reflector giving control in these two planes.

The reflector form it of Figures 1 and 2 is made of pressed glass and externally silvered as indicated at ii. It is of semicylindrical shape slightis so designed that divergence of light in longi- July 3, 1933 ly tapered if desired. Qne. surface of the reflector form is stepped'to form longitudinally extending prisms as indicated at !2 in Figure 1, while the other surface is stepped to form a series of prisms l3 extending in transverse planes. The longitudinal prisms preferably extend the entire length of the reflector form, while the transverse prisms are generally placed on the part of the reflector form which extends beyond the light source and are omitted from the part opposite the light source. Where the longitudinal prisms cover only the part of the reflector form opposite the light source, the annular and longitudinal prisms may be on the same surface of the glass.

When, as in Fig. 1, the rectilinear source S is disposed parallel with and above the center or axis 0, rays, such as SI emitted in the plane of the figure would, in the absence of prisms be reflected symmetrically to CI along the line IR. These rays would cross and diverge widely. To secure a light distribution having less spread. the prisms [2 are employed. The light will then emerge in a direction such as indicated at IR. These light rays are more nearly parallel.

The prisms l2 will not be effective, of course, to any great extent except in the case of rays perpendicular to the source; it will diminish according to the deviation from that direction; it will disappear in planes parallel to the source.

The prisms i3 shown in Fig. 2 are especially adapted to control the distribution in planes parallel to the source. In this case the natural divergence would be exaggerated by a non-prismatic reflector form and is reduced by the prisms. The rays of greatest divergence in longitudinal planes are those emitted by the extreme points S1 and S2. The point A is opposite the mid-point of the source S, so that rays 81A and 82A having an angle of incidence a give the smallest divergence. A ray such as SzJ would, in the absence of prisms, reflect normally in direction JR. If at this point a prism i8 is placed so that the ray JR is reflected in direction JR parallel to A81. all the rays falling at this point will be reflected within angle a, which will thus be a measure of the maximum angle of divergence of the reflected beam. The other extreme ray SIJ will be, for example, reflected in direction JRi.

A reflector comprising both the system of prisms of Fig. 1 and those in Fig. 2 thus permits a control of the distribution in two perpendicular planes.

The molds for making the reflector form may be made by ordinary machining processes. The prisms i3 are surfaces of revolution about the axes parallel to A8 and A32.

center C and hence the mold parts for forming them may be turned in a lathe. The prisms l2 are straight and the mold parts for forming them may be formed by planing.

Figs. 3 and 4 illustrate the case of a reflector or form I silvered as indicated at l5 and provided with prisms l6 modifying the distribution in the perpendicular plane to the source, and of which the longitudinal sections have special curvature determined in the function of 'the desired distribution.

The profile in the plane passing along the source S may be, for-example, formed by two parabolic elements having their foci respectively at the ends S1 and S2 of the filament and their In effect, as ,before, the least divergencethat one can obtain is divergence 2a. For a ray such as S21, we will have in the case of a reflecting cylinder a reflected ray I'R very divergent. In giving to the corresponding mirrored portion a parabolic form with focus at S2 and axis parallel to ASi, the ray S21 will be reflected according to direction IR parallel to ASi, all the other reflected rays being included in this angle of divergence.

The reflector thus constructed will, therefore, be of circular section in transverse planes and of parabolic section in longitudinal-planes: and will have prisms disposed parallel to the source. The mold can be mechanically turned and the prisms cut on a lathe.

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 understood that the particular forms shown are but a few of the two forms. Various modifications and changes being possible, I do not otherwise limit myself in any way with respect thereto.

Whatis claimed is:

1. In a luminair, the combination with a long light source of a trough-shaped reflector composed of a light refracting medium externally mirrored and in which the light source is longitudinally disposed, said light source being positioned within the reflector so that lines drawn from its center and an end thereof to the vertex center of the reflector make an angle a, the.

light refractlng medium having longitudinally extending prisms which increase the angle of reflected light relative to the normal to the profile to decrease the concentration of light reflected in transverse planes, the reflector also having a conformation which decreases the spread of reflected light in longitudinal planes and forms such reflected light into a beam moderately divergent in longitudinal planes, the conformation of the lateral end portions of the reflector being such that a ray of light reflected by said end portions will make \with a line parallel to the line joining the centers of the light source and reflector an angle not greater than angle a, the ends of the reflector being open to allow the escape of said moderately divergent beam.

2. In a luminair, thecombination with a. long light source of a trough-shaped reflector composed of a light retracting medium externally mirrored and in which the light source is longitudinally disposed, the light refracting medium having longitudinally extending prisms which increase the angle of reflected'light relative to the normal to the profile to decrease the concentration of light reflected in transverse planes,

the light retracting medium having transverse prisms which reduce the angle of the reflected light relative to the normal to the longitudinal profile of the reflector and form such reflected light into a beam moderately divergent in longitudinal planes, the ends of the reflector being open to allow the escape of said moderately divergent beam.

3. In a luminalr, the combination with a. long light source of a trough-shaped reflector com posed of a light refractlng medium extemallymirrored and in which the light source is longitudinally disposed, the light refracting medium having longitudinally extending prisms which increase the angle of reflected light relative to the normal to the profile to decrease the concentration or light reflected in transverse planes, the light refracting medium havingintemally disposed transverse prisms which reduce the angle of the reflected light relative to the normal to the longitudinal profile of the reflector and form such reflected light into a beam moderately divergent in longitudinal planes, the ends of the reflector being open to allow the escape of said moderately divergent beam.

4. In a luminair, the combination with a long light source of an externally-mirrored, troughshaped prismatic reflector in which the light source is longitudinally disposed, the reflector being ,of substantially semi-circular transverse profile and provided on one surface with longitudinally extending ridges out of parallelism with the opposed. surface and disposed to increase the angle of emission of the reflected light relative to" the normal to the profile of the reflector, whereby light radiated in transverse planes is decreased in divergence, the ends of the reflector having semi-circular prisms in transverse planes.

5. In a luminair, the combination with a long light source of an externally-mirrored, troughshaped prismatic reflector in which the light source is longitudinally disposed, the reflector being of substantially semi-circular transverse profile and provided on one surface with longitudinally extending ridges out of parallelism with the opposed surface and disposed to increase the angle of emission of .the reflected light relative to the normal to the profile of thereflector, whereby light radiated in transverse planes is decreased in divergence, the ends of the reflector having semi-circular prisms in transverse planes and placed on the surface of the reflector opposite that which carries the longitudinal prisms.

6. A reflector for long light sources comprising an externally-mirrored, trough-shaped prismatic reflector form having longitudinally extending prisms and adjacent its ends transverse prisms.

'7. In a luminair, the combination with a long light source, of a trough-shaped reflector comprising an externally mirrored light refractor, the reflector being of semi-circular cross section in transverse planes and having longitudinally extending prisms parallel with the light source, the trough being longer than the light source and having a cross section in longitudinal planes composed of two parabolic elements each having a focus at the opposite end of the light source and an axis parallel to the rays of minimum divergence.

MAURICE EXELMANS.

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