We have developed a thin type rear combination lamp comprising a parabolic cylindrical reflector and a Fresnel lens with linear lens cut (hereafter linear Fresnel lens).
Currently available rear combination lamps are either reflector or inner lens type. The reflector type uses the paraboloid of revolution reflector, and the inner lens type employs a Fresnel lens. In both types, the filament of bulb is placed at the focus of the paraboloid or Fresnel lens.
An inner lens type rear combination lamp can be thinner by employing a Fresnel lens of a shorter focal length. This is the reason why most of the lamps classified as the thin type are inner lens type.
However, the inner lens type has an inherent shortcoming that “with a shorter focal length, difference of brightness at the lamp center and the periphery is increased”. For this reason, efforts for the design of a thinner lamp have their limit.
We have developed a rear combination lamp in which a cylindrical parabolic reflector is combined with a linear Fresnel lens in order to reduce the luminance difference at the center and the periphery, and whose thickness is about one-half that of the inner lens type rear combination lamp. We report the principle, structure, and photometric performance of the lamp developed.