Blackbird is 20 inches from canopy.
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I’d second that, I run a 550 R-Spec which is an actual 510 watts at the wall with the Inventronics 480w ballast, so 127w per QB288. I can’t run it closer than 18" without stress praying. I could use more edge light in my 4x4, but the center 2x2 or 3x3 is plenty bright!
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I wonder how many people believe that to be a good sign, I’ve seen so many be happy when they do that, and I went with it… LIKE A FOOL.
Dimmed my light to the minimum and it’s gonna stay like that until they relax again. 
Thank you all for your input, I’m glad I made this thread.
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I gradually increase light intensity over the 1st 28/32 days, I’m not in a hurry to hit full power, all plants aren’t equal some are more sensitive to light and some can take insane amounts.
I’ve always associated praying leafs with healthy plants because the plants are bouncing with health when displaying it during bud setting, but idk for sure that’s only my observations.
The end of the day is a good time to check for light stress, ime if they’re droopy the light needs backed off.
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have played around with “light” intensity - see the benifits but this go-a-rond giving them “full” light at present – UV the last 4 weeks of flower with decreased light over the last 4 weeks also. QB from Budget LED don’t have a #"ed dimmer - Dam !! next board will have them
I had never heard this. Everyone always celebrated plant hallelujahs! Maybe I’ll back my HKG 300 Rspec back from 90 percent to 80.
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Just turned the light on, significant new bud growth overnight again, still praying though, so today again on very low setting.
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I usually let em have it during flower.
But I keep reading that 75% may help yield better results.
Good thread, following. 
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I have mine dimmed for the first 3 weeks of flower THAN I go full blast… but I watch the plants for stress signs and if I see any I back off a little. But all the plants lately have been eating up the lights
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I’m in week 6 of flower now with individual dimmable QB LED panels for each plant. The stretch is long over but I kept the distance between the light and the top bud at 18" as they grew. That’s the manufacturer’s minimum suggested distance.
I think @ReikoX provided these helpful guidelines for the intensity at different growth stages:
100 - 300 PPFD for seedlings
300 - 600 PPFD for veg
600 - 1000 PPFD for flower (adjusted as the plant reacts)
Those ranges seem to work for everything I’ve grown with little variation between strains.
But the catch is that you need to be able to measure the light intensity accurately.
For me, the solution was the Photone app running on my phone. It’s a free download with paid upgrades if you want/need them. The basic version works with LEDs and other common light types. Last time I looked they had versions for iPhone & Android phones.
The app uses your phone camera to sample the light and reads out PPFD (basically PAR as delivered to the plant). It also reports DLI (Daily Light Integral) which gives a more complete picture of how much usable light energy is delivered to your plant each day.
I tested Photone PPFD readings against the published specs for my ViparSpectra XS 2000 lights and they were spot on. There are more precise instruments with useful features available but they are costly and Photone works great.
Hope this is helpful,
-Grouchy
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Just fyi, that app is likely phone specific to be of any accuracy at all.
Every phone uses a different light sensor so an iphone will not read the same lux as a galaxy s22 for instance. And all it can measure is lux as that’s what the sensor sees. Lux is not par/ppfd. I’d bet you’d have different readings even between different iphones. Like an iphone8 vs a 14pro max, due to the different sensors used in the phones to check ambient light values.
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Why i went to a shop and tested mine against a high dollar unit.
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The android apps I’ve tried weren’t worth downloading, I’m using a Sony zx.
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I found the photons app provides accurate information to get your lights dialed in.
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Just found this while looking for some information on ppfd for late flower.
I’m currently hitting around 1400, and the plants have all been responding well throughout. But I’m wondering if there’s any solid evidence in favour of reducing ppfd in the last 2-3weeks.
Also noticed some people confusing praying plants with an excess of light.
The praying comes from plant turgor. Its an osmotic pressure response, not a response to excess light. They’re literally reaching up, growing towards the light.
Plant leaves will start to bleach and lose colour, as well as droop downwards in cases of excess light.
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I run a HLG 600rspec and a 300 and I definitely can’t run them full power. I’ve tried and get herms or small buds up top. 60-70 % is my sweet spot. Although … maybe the last week blasting them could be good? I ran the UV also and didn’t like the results during the
whole flower cycle. Again maybe the last two weeks would be good. More tinkering to be done.
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UV is kinda tough on all life, only run it like a few minutes a day perhaps?
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Most of the excellent grow bloom journals I’ve read say that the sweet spot with HLG gear in bloom is 70%. I’ve got the HLG Blackbird and HLG UVA 30 Bar. I’m excited to hook them up and start testing these myself.
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Bruce Bugsby? Mentioned running UV for little blasts during the light cycle. Indefinitely need to try more experiments. I have the HLG UVA bar I’ve tried. I also have a reptile UVB I haven’t tried yet. I heard those need to be kept far away from the canopy. One of these days I’ll give it a go.
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