Lumen

The lumen (lm) is the unit that quantifies the total luminous flux emitted by a light source. This parameter is a good measure of indoor lighting, but it is of limited significance when it comes to supplementing the lighting for tomato seedlings. Much more important are PPFD and DLI, which determine the amount of light used by plants in the process of photosynthesis. Therefore, you should not choose a grow light for seedlings based solely on the number of lumens; you should also check PPFD and the area it illuminates evenly.