Depends what the light is. Can be anything from a few inches. Up to a few feet. CFLs can be really close. COBs need about a foot- foot and a half. And things lije LECs/HPS/MH need at least that foot and a half.
Depends what the light is. Can be anything from a few inches. Up to a few feet. CFLs can be really close. COBs need about a foot- foot and a half. And things lije LECs/HPS/MH need at least that foot and a half.