Glare Glare is any unwanted light that causes discomfort, interference with vision, or eye fatigue. Direct glare is caused by light coming directly to the eye from a source or bright surface. Discomfort or reflected glare is light reflected from a surface in the direction of the eye. Illuminance Illuminance is the density of light falling on a surface. It is expressed in footcandles or lux.
Lumen depreciation is a term that describes the normal attrition of light.
Essentially, the longer a lamp operates, the less light it delivers. Different light sources have different rates of depreciation. Louver A framed opening, as in a wall, door, or window, fitted with fixed or movable horizontal slats for admitting air and light and shedding rain. May also refer to one of the slats used in such an opening. Dirt or dust that accumulates on luminaires decreasing the total output of light, lowering the overall efficiency of the system.