COLOR OF THE LIGHTS, DURATION OF THE FLASH, USE SITUATION, AND THE AVAILABILITY, MAINTENANCE, POWER CONSUMPTION, AND COST OF WARNING LIGHT UNITS ARE FACTORS TO BE CONSIDERED WHEN ESTABLISHING WARNING LIGHT CONFIGURATIONS. CONFIGURATIONS ARE NOT UNIFORM IN THE U.S., BUT THE MAJOR TYPES OF LIGHTS ARE ROTATING, OSCILLATING, AND FLASHING LIGHTS, AS WELL AS FLOODLIGHTS AND SEARCHLIGHTS. STIMULUS-RESPONSE PATTERNS, VISUAL STIMULATION FROM EMERGENCY VEHICLE WARNING LIGHTS WHEN SEEN FROM THE REAR, SIDE, AND FRONT, AND THE PERIPHERAL FUNCTIONING OF THE EYE IN SENSING LIGHT, COLOR, MOVEMENT, AND FLICKERING ARE EXAMINED IN RELATION TO WARNING LIGHT SIGNALS. THE EFFECTIVE INTENSITY OF A SIGNAL LIGHT IS THE GREATEST DETERMINATE OF ITS CONSPICUOUSNESS, BUT OTHER PARAMETERS ARE SIGNIFICANT. THESE INCLUDE THE FLASH RATE, DUTY CYCLE OR LIGHT-TIME FRACTION, WAVE FORM AND FLASH DURATION, LIGHT COLOR, SPATIAL BEAM SWEEP, NUMBER AND SPATIAL PATTERN OF LIGHTS, AND MOTION AND ILLUMINATION SPACE OF THE LIGHT SOURCE. ALTHOUGH THERE IS NO GENERALLY ACCEPTED QUANTITATIVE METHOD FOR MEASURING SIGNAL LIGHT CONSPICUOUSNESS, DIRECT SUBJECTIVE RATINGS, EYE MOVEMENT RECORDING, AND REACTION TIME STUDIES ARE POTENTIAL BASES FOR MEASURE. THE FINAL SECTION OF THE REPORT CONSIDERS PHYSICAL MEASUREMENTS OF SIGNAL LIGHT COMPONENTS NECESSARY FOR ADEQUATE CHARACTERIZATION OF WARNING LIGHT UNITS, AND THE RELATIONS OF PERCEPTUAL AND PHYSICAL MEASURES TO PERFORMANCE STANDARDS IN LIGHTS. A GLOSSARY AND AN INDEX ARE PROVIDED.