The Effect of Environmental Conditions on Moisture Clearing Time in Automotive Lamps

The FMVSS humidity test, as described in 571.108 S8.7, for forward automotive lamps permits environmental conditions to vary within a given tolerance. Pre-soak conditions of the lamp for the test may vary. The tolerances during the soak portion of the test allow for a +4°C variation (from the initial 38°C environment) and a +10% variation from the initial 90% environment relative humidity. Tolerances during the wind portion of the test allow for a +4°C variation (from the initial 23°C environment), a +10% variation from the initial 30% environment relative humidity, and a -0.153 m/s (-30 ft/min) variation from the initial 1.68 m/s (330 ft/min) airspeed setting. Utilizing a climate control wind tunnel, this study demonstrates that the tolerances on the environmental test conditions will produce substantial test result variation. The discussion emphasizes the best environmental condition to minimize time to clear condensation for a particular automotive lamp.