Improvements In Lighting Units

Abstract

A lighting unit consists of an elliptic rotational reflector having the light source positioned in one focal point, and a convex reflector facing the elliptic rotational reflector and serving for polydirectionally radiating the light rays which are emitted by the light source and pass through the other focal point of the elliptic rotational reflector. The convex reflector has at least one cup-shaped inwardly bulging recess which reflects the light rays impinging thereon at least essentially parallel.

Description

This invention relates to a lighting unit of the type comprising an elliptic rotational reflector having the light source positioned in one focal point thereof, and a convex reflector facing the elliptic rotational reflector and preferably formed as a segment of a sphere for polydirectionally radiating the light rays which are emitted by the light source and pass through the other focal point of the elliptic rotational reflector. The characteristic feature of the lighting unit resides in that the convex reflector has at least one cup-shaped inwardly bulging recess which reflects the light rays impinging thereon at least essentially parallel.

When devoid of a cup-shaped inwardly bulging recess, the lighting unit presents the same character of radiation in all directions. A lighting unit having in accordance with the invention a cup-shaped inwardly bulging recess provides a certain directional effect on the light, and this effect can be exploited for illumination of a roadway laterally of the lighting unit.

The invention will now be more fully described in the following, reference being made to the accompanying drawing which in cross section illustrates the reflectors of the lighting unit in a preferred embodiment thereof.

1 DESIGNATES AN ELLIPTIC ROTATIONAL REFLECTOR HAVING THE LIGHT SOURCE POSITIONED IN ONE FOCAL POINT F1 thereof. The reflector 1 shall be of such a size as to entirely conceal the light source. Mounted above the reflector 1 is a convex reflector 2 with the reflecting surface facing downwardly. More precisely, the reflector 2 is formed as a segment of a sphere.

The light rays emitted by the light source are reflected by the reflector 1 through the other focal point F2 thereof towards the reflector 2 so that a polydirectional radiation is obtained within the area A-B.

The lighting unit presents rotation symmetry around a vertical axis drawn through the focal points F1 and F2, the lighting unit being carried by a post, mast or like element so as to be adapted for use as a stationary lamp, as for example, a stationary roadside lamp for illuminating a highway. A clear cover of glass or plastics shall preferably be arranged between the outer peripheries of the two reflectors 1 and 2.

In accordance with the invention, the reflector 2 has at least one cup-shaped inwardly bulging recess 3 which reflects the light rays impinging thereon at least essentially parallel, thereby providing a certain directional effect on the light.

As will appear from the drawing, the focal point F2 of the ellipse is the focus of a curve y =f (x ), for instance, a parabola. When caused to rotate about the O-X-axis, this curve will generate the inwardly bulging recess 3 in the reflector 2. The light rays impinging on this section of the reflector 2 will thus emerge from the lighting unit in parallel relationship. The size of the recess 3 is determined by the amount of light to be reflected by the recess. Normally, the recess 3 is given the size shown in the drawing so as to extend from the reflector center to the periphery of the reflector 2, thereby forming an annular recess reflecting a peripheral array of essentially parallel light rays.

The angle .alpha. by which the O-X-axis is inclined in relation to the horizontal plane H is determinative of the direction in which the light emerges from the cup-shaped inwardly bulging recess 3. By changing the angle .alpha. it is thus possible to attain the desired angle of radiation of the lighting unit.

When it is desired to throw the light along a roadway in both directions as measured from the lighting unit, the reflector 2 is provided with two cup-shaped inwardly bulging recesses 3 of the above-mentioned design rather than a single annular recess 3. When the lighting unit is to be placed laterally adjacent to the roadway to be illuminated, the light should be directed slightly obliquely forwardly to cover the roadway. This is attained by causing the longitudinal axes of the two recesses 3 to be axially offset relative to each other so as to be displaced at an angle of more or less than 180.degree. with one another. The same effect can be attained by asymmetrically inclining the reflector 2 from a horizontal plane so that the reflector edge closest to the edge of the roadway is at a greater height over the ground.

The reflector 2 may very well have more than two cup-shaped inwardly bulging recesses 3. For instance, with four cup-shaped inwardly bulging recesses 3 uniformly distributed over the circumference, an approximately square lighted area will be obtained on the ground.

The invention is not limited to the embodiment described above and shown in the drawing but can be modified within the scope of the appended claims.

Claims

What I claim and desire to secure by Letters Patent is:

1. A lighting unit of the type comprising an elliptic rotational reflector having a light source positioned in one focal point thereof; and a convex reflector facing the elliptic rotational reflector and preferably formed as a segment of a sphere for polydirectionally radiating the light rays which are emitted by the light source and which pass through the other focal point of the elliptic rotational reflector, said convex reflector having at least one cup-shaped inwardly bulging recess which reflects the light rays impinging thereon at least essentially parallel, said cup-shaped inwardly bulging recess being defined by a generated curve y=f(x) the focus of which is situated in the other focal point (F2) of the elliptic rotational reflector, said curve having been caused to rotate about its axis (O-X) through the focus.

2. A lighting unit as claimed in claim 1, wherein the convex reflector has two substantially diametrically opposed, cup-shaped, inwardly bulging recesses.

3. A lighting unit is claimed in claim 1, wherein the axis (O-X) of the curve y=f(x) through the focus is inclined in relation to the horizontal plane.