Cleaning of the luminaires, which involves wiping the dirt from reflectors and refractors, should be performed during group relamping. This periodic cleaning of the fixtures reduces the depreciation of light due to the accumulation of dirt and allows the delivery of more light per lighting dollar. Allowing the illumination system to provide more consistent illuminance throughout the life of the lamps provides the motorist with better visibility and TxDOT with a more cost efficient lighting system.