PPFD/DLI vs Light Mfg Specs

I have a MarsHydro TSW2000 LED fixture in a 3x3x6 tent. I am currently about 6 wks along with a single Blue Dream auto into her flowering stage.
I have followed mfg recommendations for fixture height & pwr level up to this point as they have coincided with what I have read to be target PPFD & DLI levels for seedlings & veg
This time around I have opted for 20/4 Light schedule just to see how it goes…
My research showed @20 hrs of light a day that around 700 be a PPFD target and DLI ideally around 40 - that is if I’ve understood correctly.
Mfg recommends setting fixture height @ approx 16” and at full power for flower.
At this height & pwr the PPFD reading is at approx 1200-1300, DLI about 75-80
I’m curious - was the 700-800 mark too low?
This morning I adjusted the fixture height & pwr to the mfg specs to keep an eye on how things develop.
Any info/advice will be appreciated!
Thanks in advance
She began flowering about 1 week ago btw

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The critical part in calculating DLI is to use the average PPFD of the grow space

In both examples, PPFD of 700 for 18 hours yields DLI of 45. If the hours are increased to 20, DLI increases to 50. (700 X 20 X .0036 = 50.4 DLI)

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@beardless Thanks. I already readjusted Light to my original height & setting. Only after a short while she showed me her disapproval.
Thanks again!

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I keep it simple and run ~1,000 PPFD at the canopy throughout the grow.


@MidwestGuy thanks!

I don’t try to measure PPFD or DLI. I turn the lights on and raise them as the plants grow and will back off power late in flower to minimize foxtailing.


The manufacturers recommendations for flowering are for photoperiod plants. They are based on 12 hours of light. You require a lot more intensity to get the right DLI at 12 hours than you do at 18, 20 or 24. Everything requires a little adjustment when you grow autos.

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