US2394992A - Lighting unit - Google Patents

K. FRANCK LIGHTING UNIT Feb. 19, 1946.

Filed June 30, 1943 2 Sheets-Sheet 1 INVENTOR. llll/PT FRANCK ATTORNEY Patented Feb. 19, 1946 UNITED STATES LIGHTING UNIT Kurt Franck, Newark, Ohio, assignor to Holophane Company, Inc., New York, N. Y., a corporation of Delaware Application June so, 1943, Serial No. 492,807

7 Claims.

The present invention relates to lighting units, and is more particularly directed toward lighting units suitable for providing both vertical and horizontal illumination in long narrow regions such as aisles.

It frequently is desirable to employ a single row of lighting units or luminaires for lighting two regions on the opposite sides of an aisle, as for example, in railway vehicles, buses, the lighting of corridors, book stacks and storage bins, and in the lighting of the cargo carrying space in airplanes. In locations such as these the problem involves the lighting of vertical surfaces of substantial extent. The embodiment of the invention to be described herein is one more particularly developed for lighting the cargo space in a cargo carrying plane.

Where elongated areas are lighted with a single row of luminaires over the center of the space and such luminaires have a symmetric distribution about the vertical axis the illumination tends to be spotty and uneven unless the luminaires are comparatively'close together. When such luminaires are spaced more widely the regions intermediate the luminaires are insufliciently lighted.

According to the present invention the system of lighting employed contemplates the use of luminaires provided with light controlling means whereby the light is spread away from the nadir a lesser amount in directions transverse of the regions to be illuminated than it is spread in directions lengthwise of the regions to be lighted. This makes it possible to direct the light emitted generally in the direction of the regions to be lighted at higher angles above the nadir intermediate the luminairesso that it reaches these more distance areas at angles'where it can be utilized more eflectively.

Other and further objects will hereinafter pear as the description proceeds.

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

In these drawings: Figure 1 is a diagrammatic cross sectional view through a region to be lighted;

Figure 2 is a diagrammatic longitudinal plan view of the same;

Figure 3 shows a photometric curve taken in the plane of Figure 1 through the center of the light source;

Figure 4' illustrates photometric curves taken in the vertical plane through the centers of Figures 1 and 2; i I

Figure 5 is a diagrammatic perspective view illustrating light distribution; v

Figure 6 is a vertical sectional view through a luminaire taken in directions of the line 8-6 of Figures 2 and 7;

Figure 7 is a top ure 6;

, Figure 8 is a section through the lens of Figure 6 taken in the direction of'the line 8-8 of Figures 2, 6 and 7 and Figure 9 illustrates a modification.

Figures 1 and 2 illustrate a region to be lighted. Here the luminaires are indicated at ID. The regions to be lighted are indicated at II, II and they are on the opposite sides of an aisle It. It will be noted that these regions occupy substantial width in horizontal planes, have substantial vertical depth, and that their longitudinal extent may be indefinite.

The spacing of the luminaires l0, I, as illustrated in Figures 2 and 5, is about one and onehalf times the mounting height as illustrated in Figure 1, and the mounting height is shown to be plan view of the lens of Figapproximately equal to the maximum widthof the area to be lighted in a typical arrangement sucha illustrated the more remote part of the floor is approximately 30 from the nadir.

If the lighting equipment were designed to havesymmetrical distribution about its vertical axis it would produce equal illumination at all points equidistant from the'flxture axis, as illustrated by the circles l3 of Figure 2. If the angle of spread were such as not to waste light on the outer side walls of the region directly opposite the luminaires, then the spread in longitudinal directions would be insuflicient to have the spots of light meet and overlap. This is illustrated by the failure of the circles I3, I3 to cross one another and overlap. Under such conditions there would be a comparative excess of light close to the fixtures and comparatively no light halfway between the fixtures, and both vertical and horizontal surfaces would be poorly lighted especially these surfaces more distant from the center of the aisle and halfway between the luminaires.

The present invention contemplates providing luminaires with light controlling means whereby the illumination may be satisfactorily built up in those areas which would otherwise be poorly illuminated so that comparatively high illumination is available and yet maintain the desired spacing of the lighting equipment.

As the radial \plane shifts from plane 6-6 through intermediate planes toward 8-8 there is a change in the steepness of the ridge surface in such radial plane and there is less lessening of the angle of incidence and of refraction and hence elevation of emergent rays above the nadir lessens until at plane 8-8 the ray direction is solely controlled by the lower ridges acting as elements of prisms whose upper surfaces are flat.

Instead of having light distribution which can readily be illustrated by a cone 5|] with a circular bas with its apex at H], such as illustrated in Figure 5, there results a distribution of light which can more properly be as confined to the shell-like surface of a non-circular cone, i. e., one whose base instead of being a circle (as at |3) is a quasi-ellipse, such as illustrated at 5| in Figures 2 and 5. It will thus be apparent that not only is the horizontal illumination improved in regions between the circle l3 and the quasi-elliptical curve-s 5| of Figure 2, but that each source improves the vertical illumination, particularly on transverse planes opposite or nearly opposite the adjacent sources.

Since it is obvious that the invention may be embodied in other forms and constructions within the scope of the claims, I wish it to be understood that the particular form shown is but one of these forms, and various modifications and changes being possible, I do not otherwise limit myself in any way with respect thereto.

What is claimed is:

1. In a luminaire, means for acting on a downwardly divergent cone of light to cause the less divergent emitted light to spread away from the nadir throughout the entire circumference at a greater angle above the nadir in two regions diametrically opposite one another than in the two regions at right angles thereto and to reduce the divergence of the more divergent light to substantially the same angle above the nadir as that to which the less divergent light is spread in the same azimuth, whereby the distribution is asymmetric in vertical planes with higher angle of maximum candlepower in the first two regions than in the other two regions, comprising a horizontal lens intercepting the divergent cone of light rays and having parallel, upwardly and .outwardly sloping prismatic ridges on the light incident surface disposed in the direction of the lower-angled high-angle light, and annular prismatic ridges on the light emitting side whose retracting power decreases from the center to a minimum and then increases.

2. In a luminaire, a point source, a substantially flatretractor having a system of parallel.

upwardly and outwardly sloping prismatic ridges on the light incident surface of minimum refracting power at the center of the refractor and reater retracting power remote from the center for diverging light in two opposed azimuthal clirections without affecting it in azimuthal directions at right angles thereto, and annular prismatic ridges on the light emergent surface, the retracting power of the inner annular prismatic ridges being such as to spread incident light away from nadir, the retracting power of the outer annular prismatic ridges being such as to deviate incident light falling thereon toward nadir whereby the angle of maximum candlepower of the emitted light output is higher above nadir in the first two azimuthal directions than in the azimuthal directions at right angles thereto.

8. A luminaire comprising a substantially point light source, a normally horizontal, substantially flat lens plate with its center below the source, the upper surface of the plate having on opposite sides of a median vertical plane through the light source parallel prismatic ridges havin variant retracting power from prism to prism, each ridge being uniform throughout its length and having a light incident surface at an angle of incidence to direct light from the source lower than would be the angles of incidence for a similarly placed flat smooth surface, whereby the angle of refraction on entering the plate'is less and the angle or the light in the plate is raised higher above the nadir and the lessening eifect on the angle of refraction and the raising of the light in the plate decreases with angular distance from the median plane, the lower surtace of the plate having annular prismatic ridges which converge the rays transmitted thereby into generally parallel directions in each radial plane and direct the emitted beam away from the nadir a minimum amount in the median plane and a maximum amount in planes at right angles thereto, and continually changing amounts in intermediate planes.

4. An aisle illuminating device symmetrical about a central vertical plane for use in an aisle with a plane of symmetry transverse of the aisle, said device comprising a light source and a refractor underneath and close to the source so as to receive substantially all the downwardly emitted light, the retractor being provided on its upper surface with a system of parallel outwardly and upwardly sloping prismatic ridges extending parallel to said plane of symmetry ot minimum retracting power at the center of the retractor and greater retracting power remote from the center for diverging light in the retractor in directions along the aisle without aflecting the light in directions across the aisle, and having on its lower surface a system of circumferentially uniform annular prismatic ridges of varying retracting power with varying diameter to concentrate light divergent from the source into an annular region whose diameter is substantially the width of the area intended to be illuminated and with a light beam intensity varying from a minimum at nadir to a maximum at the periphery of said region, the parallel prismatic ridges transmitting the light which falls on them such that it reaches the annular ridges from a lowered virtual source in such an amount that the annular prisms concentrate the emitted light in directions generally lengthwise of the aisle at vertical angles such as to direct said light on to the remote portions of said area.

7. The combination with a concentrated light source of a horizontal retracting plate below the source to accept a cone of divergent light therefrom, said plate on its upper surface carrying a system of parallel regressed prismatic ridges optically equivalent to a negative or divergent cylindrical lens surface each side of a central vertical plane through the source, and on its lower suri'ace at its center carrying a system of annular regressed prismatic ridges optically equivalent to a negative or divergent spherical lens surface, and outside this divergent system carrying a second system of annular regressed prismatic ridges optically equivalent to a positive or convergent spherical lens surface, the two systems being separated by a narrow flat area and the refracting powe of each system of annular prismatic ridge being such that the light emitted at each azimuthal direction is substantially parallel to that emitted at that direction through the flat area.

KURT FRANCK.