You searched for: “lumen depreciation”
lumen depreciation (s) (noun), lumen depreciations (pl)
The gradual loss of efficacy of a lamp over time, typically caused by the loss of chemical additives in the lamp and wall darkening in the arc tube: Lumen depreciation can be indicated by a curve depicting the pattern of decreasing lucid output.

The florescent illumination in Mildred's kitchen started to flicker, apparently because of the lumen depreciation in the tubes.

 
This entry is located in the following units: -ation, -ization (-iz[e] + -ation); -isation (British spelling variation) (page 60) lumen-, lumin-, lum- (page 3) preti-, prais-, preci-, pric- (page 2)