U.S. flag

An official website of the United States government, Department of Justice.

Effects of Warning Lamp Color and Intensity on Driver Vision

NCJ Number
Date Published
October 2008
54 pages
This study examined how the colors and intensities of warning lamps on emergency vehicles influenced both positive and negative effects on safety in both daytime and nighttime lighting conditions.
Under the three test conditions, major differences were found between day and night conditions. Test drivers' search for lamps was easier at night, and their search for pedestrians near the emergency vehicles was easier during the day. The large difference in safety effects of warning lamp color and intensity under day and night conditions add support and some level of quantification to the view that the most significant improvements in warning lamps may be in adopting different light levels for night and day. Over the range of lamp intensity used in the testing, there were improvements in safety with higher intensity for the lamp during the day, but safety performance on warning lamps at night was uniformly effective, with no improvement in safety occurring with greater lamp intensity. Lamp intensity and color had little effect on the visibility of pedestrians near the vehicle during either day or night testing. The testing also found that more use of blue light during both day and night is best. Another recommendation is that color coding be used to indicate whether or not emergency vehicles are blocking traffic lanes. Study participants were selected to be reasonably representative of the driving public. Two groups, based on age, were chosen to ensure that some estimate could made of how warning lamp effects might differ with driver age. A static field setting was used to simulate the most important visual circumstance of situations in which drivers respond to warning lamps in actual traffic. Four lamp colors were used (white, yellow, red, and blue); all four colors were presented at two levels of intensity. 3 tables, 27 figures, 13 references, and appended sample of study materials

Date Published: October 1, 2008