Light distance

12-18 inches (30-45 cm) is usually the vaguely generic recommendation for LEDs unless the manufacturer states otherwise. If you are trying to dial in the maximum light intensity, a good light meter may be a next step. I order my own LED bars directly from the factory in China and have to use an ePAR meter to dial in the PPFD my lights. Considering that lighting can be a serious limiting factor in growth, the ePAR meter was well worth the money. We spend a lot of money on nutes and the devices to check those expensive nutes, but never the lights. Lights cost good money - why not acheive your ideal PPDF at all times.

Well you’re not getting 1800 at 25%.. that’s why I prefer not to run at lower dimmed rates cuz you’re kinda guessing on umols unless you’ve got a meter or specific dimmed numbers from the light company. My guess is something like 24” is fine at 25% if it’s a bar light

It's going to depend on what stage your plants are in.. check the manufacturers recommendations... Good luck..