There are some interfering elements, which are able to influence the signal functions of a car's rear light. One
of these elements is the sensitivity to external light sources, which is able to affect the intensity of the rear
lamps by the impact of direct sunrays in a flat angle. Recognition of the signals could be made more difficult
or impossible. This effect is called phantom light effect. Today the regulations of the ECE do not contain these
influences. To investigate the meaning of the effects to the traffic safety, there has been a test with a sun
simulator. The task of this test is to measure the luminance of signals from different actual taillights with and
without sunlight. Another part of the investigations are some psychophysical tests involving about 20 persons.
The dimension of phantom light effects at taillights will be quantified by the analysis of the luminance pictures.
With these cognitions some possibilities to reduce the phantom light effect with little changes in the optical
design of taillights will be performed. One example will be shown.