An investigation has been made to determine the relative rates of fading of colored materials by daylight and artificial light. The effects of various factors such as illumination intensity, spectral character of the radiation, temperature, humidity, etc., have been studied. Colored silk ribbons were used for the tests. The average results of tests on 23 ribbons show that exposure to sunlight and skylight at 3,900 foot-candles for 11 hours, or to skylight alone at 450 foot-candles for 40 hours, will cause as much fading as exposure to 500 foot-candles from tungsten lamps for 100 hours. Also, that approximately equal degrees of fading will result from exposures to tungsten filament radiation for 100 footcandle-hours, skylight for 34 footcandle-hours, or to sunlight and skylight combined for 77 footcandle-hours.