Thanks for asking.
The distance of the LED grow light from the plants affects light intensity. The farther it is the less intense and the closer it is, the intensity also increases. But it's a little more complicated than that.
Light intensity is measured in PPFD (umol/m2s). We have made a detailed intensity map of our Z2 LED grow light lamp that displays the intensity it reaches at certain distances and how far the lights spreads out before it starts to fade. We can send the map to your email but you can check out our website as well. Here is the link: https://www.ledtonic.com/pages/z2-product-info.
I'd like to say that there is no specific number to follow as there are many factors that dictate the amount of light a plant can handle. A few of them are temperature, humidity, water requirements, and nutrient requirements among others.
Generally, we recommend 100-300 PPFD for seedlings. Start at the lower intensities (higher distance) and lower the lamp a little each day to increase intensity.
Shocking the plant by suddenly giving it more than it can handle can result in tip burn, twisted leaves, and stunted growth.
Aim for 100-150 PPFD just when your seed is breaching the surface, and increase intensity in even increments slowly. Try to aim for 300 PPFD when your plant is around 2 inches tall and keep increasing slowly, up to around 400-500 PPFD during vegetative.
When it is time for flowering, aim for 600 PPFD or slightly more. Again, this is best done in increments. The distance will most likely be decreased automatically by the plant when it is growing taller and taller, towards the lamp.
Seedlings: 100-300 PPFD (30
= 191 PPFD center spot value) = 293 PPFD and 18
Vegetative: 300-500 PPFD (24
= 530 PPFD) = 600 PPFD)
flowering: 600 PPFD (16
You can try to carefully work your way from 16
to 12. You see, 12" will result in 871 PPFD and this is absolutely doable but we only recommend it in the late stage of flowering.
It also requires all other criteria to be met, as I mentioned before (humidity, temperature, etc.). Keep an eye on your plant if it looks healthy and thriving.
Experiment with lowering the lamp an inch and give it a couple of days. If you see signs of stress, tip burns, or leaves curling, raise the light a couple of inches.
I hope this was helpful. Let me know if anything was unclear or if you have any other questions.