The lumen (PPF) output of an Inda-Gro induction lamp is expected to have depreciated after 100,000 hours to no less than 70% of the initial rated output. When any lamp is new, its light output is at the maximum. As the lamp operates, various processes (plasma, chemical, and thermal) within the lamp causes a gradual reduction of its lumen output. The degree to which the actual light out put decreases with operating time is referred to as lumen maintenance.