How much is too much Light?

I am in Day 9 of flower; day 47 from seedlings. I recently bought a 320W XL QB324 LED from HLG. I noticed in my 4x2 tent the corners weren’t as lit up as center unless I really pulled the lights up.
I have decided to also put in my Blurple LEDs which are about 200w each wall. I used them for veg and they are very bright. Had to raise them a lot to get my girls to stretch.

Question is: Is this too much light? Is there such a thing? Does this cause fox- tailing?

Another issue is I over crowed with 4 plants. 2 WW and 2 Super Lemon Haze. (I plan on only 2 Blue Dream in 5 gal smart pots next grow).So I think I need serious light.

I have great heat control with an A\C line directly through the intake fan so no issues there.

What are your thoughts @dbrn32 @anon95385719 @Countryboyjvd1971 or @raustin

I wish I could help u here. When it comes to lights I am I big noob. This is only my 2nd grow indoors. I have always used the strongest light on the market. And the cheapest. The sun. But @dbrn32 @anon35207245 or @Aolelon have a lot of knowledge here

You should probably be good around 24". How close do you have it now?

I don’t think you have too much light, it looks good.

I think I have it at about 18" or so now @Aolelon. Thanks also @raustin. I had just a tough of pH issue a while back and tiny amount of nute burn but so far so good for first grow.
:rofl::stuck_out_tongue_winking_eye:Still a lot of room and time to screw it up!!! Thanks for the help.

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They look good . I have the same light and same size tent . A few of my top leaves turned brown after a week of running the dimmer on high and height was 18’’ . Dimmer now is about 60% power and height is approximately 22 inches .Tent temperature has never been over 78* with the QB , even on high . I think you will be ok . Just keep an eye on it and adjust .

I think the light was too close .

Whoa I might just raise up a bit higher then. I am at full light and 18 like you were so I think I will match up your settings if it worked out ok for you.

I would definitely do 24". You would get much better light spread and more even light levels to your plants.

I’m still a noob and I packed way too many in my 4x2 and they turned out awesome.


Plus I had like 5 different strains which was brutal for first grow. Lol

Anything over about 800 umols/s/m2 is going to be point of diminishing returns on ambient co2. In my opinion, that is where you can start talking about too much light. I haven’t seen integrated sphere data, but if I extrapolated the data correctly, ppf on version 2 320 kit should be around 720 umols/s. In 8 square feet that should put you at ppfd of about 970 umols/s/m2. If you have version 1 boards, I’d expect that ppfd to come in around 900 umols/s/m2.

Not ridiculous, but probably a little more than you need.


I’ve read of some people effectively using 1500 umol/s and lowering their day to 6 hours. Not that it changes much.
You really want to aim for around 30 mols. 20 - 25 in veg and around 30-35 is the max in flower. With co2 this can be a bit higher.
A lot of people are going by watts /sqft which is a good basis, but an even better one is to figure out how many umol/s/m2 your light is putting out and then figure out how many mols/day you are aiming for and to try and hit that.
For those who want to figure it out, you would take your mols you want to hit. Let’s say 32 mol / 18hr photoperiod / 60 minutes / 60 seconds = 0.000494 moles. This is the amount of moles delivered per second per square meter.
0.000494 × 1,000,000 = 494 umol/s/m2
So to hit 32 moles. You would need to average around 494 umol/s/m2 with an 18 hour day.
I’ve heard anything over 40 moles is pretty much a waste without co2, but every grow is different so you really just have to adjust accordingly

Theres also a pretty easy way of figuring out the ppfd of your light if you know the CCT. Take your lumens and divide by 69 for 3000k, 71 by 3500k. I’m unsure of what you divide by if higher or lower, maybe 73 for 4000k.
So my 3000k QBs if putting out 40000 lumens I divide by 69 and that would be 579 umol/s. I dont think its 100% completely accurate but its a nice baseline.
It might only be true with white LEDs I’m not 100%

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I am a noob also. I have 2, 1000w LED’s in a 4’ x 4’ space. The lights are permanently fixed to the ceiling, about 7.5’ high. I have 3, 7-gallon smart pots in there now. They have been in the flower stage for 10 days now. They have stretched out to about 1.5’ from the lights now and formed into a thick bush top to bottom. I may try cutting back to 1 light if they get much closer.

3000k qb 288 at 2300ma ppf is about 290 umols/s. If we’re talking about 2 boards, pretty damn close.

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usually too much light is a good thing , but it gets to the point of diminishing returns unless all other parameters are up to speed. Co2 becomes necessary with perfect environmental controls and nutrient levels.

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