A research project has been completed to determine if commercially available blue coated lamps provide visual benefit for nighttime driving over standard tungsten halogen lamps. As an esthetic option, tungsten halogen lamps with an absorptive coating have been developed to mimic the appearance of HID lamps. The transmission of these coated lamp results in a continuous output spectrum, like standard tungsten halogen, but with a lower “yellow” content, giving an appearance similar to HID lamps.
Aside from esthetic reasons for using blue coated lamps, there is also evidence that the spectral output may provide visual benefits over standard tungsten halogen lamps in nighttime driving. While driving at night, off-axis or peripheral vision is in the mesopic response range and the eye's sensitivity shifts towards shorter wavelengths or “blue” light. Since the spectral output of blue coated lamps is designed to be weighted towards shorter wavelengths, and since the photopic light output is maintained at standard tungsten halogen levels, a relative increase in visual sensitivity may be seen.
An experimental investigation is described that examines nighttime visual performance and subjective preference of blue coated automotive lamps. Subjects perform a visual tracking task while seated in the driver's seat of a test vehicle. Simultaneously, small targets illuminated with test forward lighting and located at various angles in the periphery are activated, with subjects releasing a switch upon detection so that reaction times can be measured. Reaction times greater than 1 sec are considered misses. The potential consequences of these results on driving safety and on the development or refinement of blue coated lamps are discussed.