Northern Lights blinds small eyes

If in vegging should be roughly 24 inches and flower a little closer like 18. Of course this depends on how strong your light is and if you want it to stretch more. Some led lights are too powerful and need more space. I use a inexpensive light meter to gauge the ppfd of the light and adjust appropriately. 2000 ppfd is suppose to be equivalent to full sun. Personally I aim for around 1200 to 1600 range but I grow several plants in different stages under same light. I just prop plant containers up closer to light for smaller plants. Hope this helps and happy growing.