Effectiveness of clear-lens turn signals in direct sunlight

Abstract

Current front turn-signal lamps in the U.S. predominantly use clear lenses and amber bulbs. However, clear-lens lamps are more susceptible than amber-lens lamps to sun reflections that may be interpreted as turn signals (sun phantoms). In this study, we quantified the relevant photometric differences in direct sunlight between these two lamp types for a large sample of current lamps, and presented inferences for likely effects on driver performance. Although our data confirm that, in general, clear-lens lamps are likely to provide signals that are less discriminable, the variability within each lamp type is large. In other words, some clear-lens turn lamps currently on the road are likely to be resistant to sun phantoms, and some amber-lens lamps are not. The report also discusses the desirable photometric levels of turn signals for effective performance in direct sunlight. Finally, it is argued that an indirect benefit of turn-signal lamps that are near low-beam headlamps is that, because of their higher required intensities, they are likely to be less susceptible to sun phantoms than lamps farther away from low beams.