Illumination – Light source and modifier – Including reflector
Patent
1992-11-10
1994-11-15
Cole, Richard R.
Illumination
Light source and modifier
Including reflector
362309, 362310, F21V 1304
Patent
active
053654188
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to lights and in particular to signalling lights.
The invention has been developed primarily for use with signalling lights for traffic control and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use and is also suitable for warning and indicating lights.
BACKGROUND ART
The function of traffic signalling lights is to project a beam of light at specific angles through an aperture of predetermined cross sectional area. Endeavouring to achieve this end, an internal light source provides illumination to a suitable lens. To facilitate more efficient illumination a reflective surface, usually of parabolic shape, is employed to re-direct toward the lens light from the internal source which would otherwise be wasted. The combined action of the reflective surface and reflection from the filament and envelope of the internal source also causes light from external sources, such as the sun, to be re-directed toward the lens, which can lead an observer to believe that the light is on, when in fact the internal source is off. Such an occurrence is known as a "phantom signal".
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a relatively simple signalling light which overcomes or substantially ameliorates the disadvantage of the prior art.
According to the invention there is provided a signalling light including a light source, a lens of the type commonly described as a fresnel lens to provide an output beam, and a reflective surface partially surrounding said light source defining an opening directed toward said fresnel lens and having an area substantially less than the area of the fresnel lens so that the amount of light that is available for the production of phantom signals is reduced with respect to the amount of any external light that enters via the fresnel lens and wherein in use, a portion of the fresnel lens is directly radiated through the opening by light from the source and the reflector directs substantially the remainder of the light from the source toward said fresnel lens to substantially evenly illuminate all of the available fresnel lens area.
Preferably, the reflective surface and the lens are fixedly spaced by a non-reflective support means. fresnel lens, for providing different angular spread of the light in the horizontal and vertical directions.
Preferable also, the area of the opening of the reflective surface is one half or less of the area of the fresnel lens.
In a preferred form the reflector is shaped so that the combination of reflected light and direct light results in a substantially uniform illumination of the surface of the fresnel lens. The shape of the fresnel lens surface is dependent upon the geometric arrangement of the source, reflector and fresnel lens.
It will be apparent that the fresnel lens collimates the light passing through it which originates from the internal light source.
BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention will now be described, by way of example only, with reference To the accompanying drawings in which:
FIG. 1 is a cut-away side elevation of a signalling light according to the invention.
FIG. 2 is an enlarged cut away section of the fresnel lens of FIG. 1 showing the path taken by light originating from the light source.
FIG. 3 is the fresnel lens of FIG. 2 showing the path taken by light originating from an external source.
MODES FOR CARRYING OUT THE INVENTION
Referring to FIG. 1 the signalling light 1 includes a light source in the form of an electric globe or bulb 2 and fresnel lens 3 to provide an output beam. A reflective surface 4 partially surrounds the electric globe and defines an opening directed toward the fresnel lens 3 which has an area substantially less than that of the fresnel lens. A portion of the fresnel lens is directly irradiated through the opening by light from the globe 2, and the reflective surface 4 direct
REFERENCES:
patent: 1581491 (1926-04-01), Rhodes
patent: 1626615 (1927-05-01), Kirby et al.
patent: 2124417 (1938-07-01), Hamel et al.
patent: 3428800 (1969-02-01), Levin et al.
patent: 3818218 (1974-06-01), Heenan et al.
Cole Richard R.
Commonwealth Scientific and Industrial Research Organisation
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