What are Initial Lumens?
Also called “initial light output,” initial lumens refers to the amount of light produced by a lamp after 100 hours of operation.
Why Does the Light Output After 100 Hours Matter?
The amount of light produced by a light source is not consistent throughout the lifespan of the lamp. While LED technology has advanced enough so that top-tier LED grow lights see very little light depreciation over time, even the most cutting edge lights lose some lumen output as the lamp ages.
Fluorescent and HID lamps are especially complicated when it comes to light output over time. These luminaires contain light-generating chemicals that will not fully settle or stabilize until the lamp has seen around 100 hours of operation. And the lamp will not produce optimum light until the chemicals have stabilized. Initial Lumens, therefore, measure light output when the lamp is at its absolute best: just after the chemicals have settled but before the light quality begins to diminish.