Different plants require more or less light and heat to grow properly, so it is highly important to determine the right formula for your indoor garden before planting any seeds. Generally speaking, the stronger the light, the further you’ll need to hang it from the seedlings to prevent them from burning or being damaged by too much heat.
A 1000-watt LED grow light should be hanged at a minimum of 15 inches from the plant. However, depending on the strength of the light, you shouldn’t place the light higher than 30 inches above the seedlings if you want them to still develop normally.
Smaller-sized lights like the 400-watt ones should stand around 20 inches above the seedlings without losing vitality. Keep in mind that this only applies to LED lights that don’t generate too much heat. By comparison, a 1000-watt HID grow light should be placed 16-31 inches away from the plant to prevent burning it.