Abstract
Optical radiation sources represent effective means of communicating warning information to travelers entering restricted areas in vehicles or on foot. Warnings can be communicated independent of language barriers to travelers not equipped with radio or satellite communication devices. The objective of this research is to document what qualities of pulsed monochromatic light stimuli are most likely to be interpreted by observers as warning signals. In two experiments observers viewed a realistic urban scene projected onto a display screen. At different times simulated warning signals with varying characteristics appeared. Observers made decisions about whether the signal represented a warning or not. The light stimulus parameters investigated included color (red-only, white-only, green-only, red-white, red-green, white-green), flash frequency (CW, 3-Hz, 10-Hz), and brightness. In experiment 1 ambient illumination represented nighttime viewing conditions. In experiment 2 the ambient lighting was consistent with dusk or dawn viewing conditions. Results of both studies indicate that higher flash rates, use of red, and increased brightness were consistently associated with perceptions of warning. Implications of these findings for the design of optical radiation warning systems to protect secure areas will be discussed.