Investigation of Light-Emitting Diode (LED) Point Light Source Color Visibility against Complex Multicolored Backgrounds

We evaluated the threshold visibility illuminance for signals sent from light-emitting diodes (LEDs) of 5 colors (green, red, white, amber, and blue). Experiment 1 involved controlled laboratory measurements of LED visibility against selected uniformly colored backgrounds. Experiment 2 involved outdoor measurements of LED visibility against camouflage patterns in natural daylight. Five camouflage patterns were used (MARPAT Woodland, Desert, and Navy, and Arctic and Swiss Alpenflage). These camouflages represent a variety of battlefield environments. Indoors, LEDs were displayed before 5 uniformly colored backgrounds selected to best match the combined chromaticity of the camouflages. Participants used the method of adjustment to vary the brightness of the LEDs until each LED color became barely perceptible, and barely imperceptible, providing visibility thresholds for each LED against each background. Results show the LED illuminance required to achieve threshold average visibility increases as background illuminance increases, the Arctic (white) backgrounds required the highest LED illuminance to achieve threshold visibility, and the red LED color was visible at the lowest illuminance against all background materials at the highest background illuminance values.