LED light distance from seedling?

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you need a light meter . Then convert it to par for the proper stage.
Suggest height idk ? I do not know your light . But i want to say. make it as bright as a led bulb you have in your house lamp when your hand is about a foot away . No brighter . Or lets say the light was full blast i would place it 4 foot above .

 

They should have ur answer on their web page

 

This image below is new (provided I found your actual light model, looks like S33), everything below is copy paste on lights mate, should take some of the mystery out. (May want to double check "par map" or "ppfd map" for your light model and see if other images give you similar numbers) These are the numbers your light is supposed to put out at 100% and varying heights)


Numbers show roughly how many microromoles per second (umol/s) of light hit the plant based on the height per picture, falling off as you hit the edges of the 3x3 coverage area of the light).

If you have an intensity knob, thats straight linear math. So at 18 inches and 25% intensity you "should" be hitting about 300 umol/s dead center (1206 x .25 or 1/4 for the 25% intensity.)

If you adjust by height, light is reduced to 1/4 of the value shown, every time you double the distance from the plant. So at 100% and 12 inches, the light puts out a max of 1702 umols/sec. IF you double the distance (raise light from 12 inches to 24 inches above plant), the light drops to approx 425 umol/s on that dead center spot.

This is important because your plants want different amounts of light as they grow. you'll find all sorts of numbers around the internet heres some numbers from the dutch passion blog, I typically give my plants more light than they recommend, but I only do that because I've had numerous grows where I gauged hands on how the plants responded.

So anyway, all around the internet you can find various numbers like this with recommendations.
Seeding = 100-300 umol/s
veg = 250-500 umol/s
flower = 600-1000 umol/s

The overall healthier your plants are, the more light they will be able to use and grow, so healthy plants can usually handle numbers much closer or even about the high ends given here (but by the time you have plants thriving at 1000+ umols, you'll get greatly diminished returns from anything beyond without supplemental CO2)

Likewise, stressed plants (not enough nutrients, water, wrong PH in the medium) will tolerate less light before they start to get light stress. Whole plant works together.

So sad, deficient plants like this, might get stressed if you give them more than 300 umol/s in veg, and will only get worse quicker if you keep upping the light intensity without correcting the problem (in this case it was various deficiencies plus under watering.

Second pic shows a veg plant at same age, healthy, good soil and water schedule, happily sucking up 600+ umol/s because its a strong healthy plant in an environment that keeps it "happy" and "hungry".

Start low and slow, if the plants look good up the light a little every few days (or as they get bigger), adjusting your light around the very general and approximate ranges, then "dialing it in" with the the math and your own observations on your plant to get them the most light they need, without frying them (too much light will kill a plant just as surely as none at all)

Best of luck mate, the unfortunate reality is that every grow is usually a little different, and although reading can impart a lot of knowledge, for me at least it didn't really "click" until I had a few grows worth of hands on experience watching what the plants do to various adjustments in light, water, nutrients etc.

Don't get discouraged, it took me almost 2 years from my first grow to the point where I felt I was producing buds I could feel "proud" of. Barring any usual issues (disease, pests, mold) every grow you finish, no matter how crappy, will exponentially increase your skill for subsequent grows!


Anyway hope this helped, but the Sunday wake and bake session is over for me, time to go face the day

 

I am using 1000W Prime Grower Horticulture LED Grow Light. I keep my light 18 to 24 inches away from the plants and it's working great for me.