DLI calculation for 650R

@dbrn32 @fano_man Folks I am trying to calculate the DLI/moles needed based on distance and intensity on the dimmer. I have 2 hlg 650rs in a 8x4, so consider 1 650 in a 4x4.

Ive done my best at researching this but am confused and I don’t have the means now to buy a par meter. Ive seen this mole(s) term thrown around in both seconds and also a much lesser number for /day. Further, on for the 650 here is independent study, but I have no idea what the heck this is talking about.

Net net is I am trying to figure out how close and what intensity on dimmer I need to hang to optimize DLI.

Im sure this is rambling incoherence but maybe not lol


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To calculate dli:

Ppfd x (3600 x your light hours) / 1,000,000 = DLI


Ok so I am straight of the ppfd is 900 and at flower that would mean dli is 38.8?

Is there an optimum for cannabis at each stage?

Thx @Bobbydigital !!

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That’s right. Around 35 in flower will get you there. Around 45 for veg. Which is about 700ppfd for 18 hours


Solid @Bobbydigital I am learning fast thanks to you! So this is the ppfd for my light in a 2x2 (they show 3x3 and 4x4). Anyway, as you can see the ppfd varies. When making this calculation, are you taking the center most point under the light and as such, the highest ppfd?

You’re looking for the average ppfd for the area at a specific height. Haven’t seen a map with that many points of reference.


And that’s just the 2x2 lol. I’ll reach out to the mfg

:clap::+1: don’t know how many times I’ve had to type this!


Here is ballpark cheat. Hlg-650r ppf=1770 umols/s. 4x4= 1.49m². Definition off ppfd is umols per second per meter squared. So…

1770/1.49=1188 umols/s/m². That is ballpark because you will have some losses. But is indeed the total amount of light per square meter.


OK now Im back to complex math. I thought Im looking for DLI 35-40. The formula @Bobbydigital made it simple to calculate. Just plug in the 796 that HLG shows for 30" and that comes to like 34.3 DLI. So if you want it a bit higher, drop the light a bit.

@dbrn32 you’ve seen enough of me to know what the heck I am trying to figure out. This gets back to determining the right dim percentage or height of light so that I am not overloading or wasting light. Since I cannot go any higher in my tent, I will be roughly at that 30" mark. And maybe that’s why a long time back you just said use 80% and I have wasted a lot of time since I didn’t just listen to you lol.

Or just buy a damn meter :slight_smile:

I have learned a ton on this topic and TDS just the past 24 hours, this is great. Thx gang.


He’s just saying the average ppfd for that light is 1188 in a 4x4 space. So that’ll need to come down by raising the light or dimming. If you can find a map of theirs that has the average ppfd of 800 at x inches, run it at that height. If they don’t then it’s a guessing game without a meter.


OK, yes, I found it by clicking into their independent study. I don’t know what 6" square grid means, but I take it to mean that the average at 30" is 796. The image is cut but toward the bottom is center. I guess that’s why for this HLG light compared to other ones, the canopy height is ~6 inches higher than others due to the power of the 650.

If this is the case, and I am running only at 50%, I am missing out on a lot and per the other thread my perceived issues with light burn (which the plant showed hardly anything) could have been related to not increasing my nutes along with the lighting. Those could have been nute deficiencies not the light.

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Dimmimg gets technical because light output isn’t linear. The more you dim your light it gets more efficient. So at like 50% power is maybe only a 40% reduction in light output. But thumb eyeball should be close enough to attain what you’re looking for.

I would shoot for flowering at roughly 70-80%


Thanks @dbrn32 which is exactly what you told me 2 month ago before I got that light LOL.


Right or wrong I’m at least consistent haha


Basically they measure every 6 inches.


Every time I feel I get smarter learning an acronym, its something like this that dumbs me right back down haha. Thx @Bobbydigital


Sry been busy … team’s got you covered …anything over 800 ppf average is over kill without co2 supplementation… the most even spread I’ve noticed on several lights was in the 18 to 22 inch range … ppf is pretty closer to as uniform as they get unless you got a really large spread like a strip light or a scorpion there light sources are pretty evenly spaced out over the canopy… cluster lights like 650r 600r they definitely have big contrast of numbers to edges I would love to have a meter

Good morning @dbrn32 @fano_man @Bobbydigital @Myfriendis410

Well I cranked up the light one notch to what hlg states is 60 percent. One issue I’m having is the fan is kicking on more frequently as I’m exceeding 80. So my humidity is down to about 35. Not horrible but I’ll get the humidifier back in there.

But look at these two. One is the GG that tends to look droopy but looked great yesterday. I’ll see if I have before and after. And the other pic is from a different strain. Some look like this (not as bad) others don’t which confuses me.

I watered wed night. They don’t feel like they need it yet. Although the gg seems to be thirstier. For now I turned the light back to 50.

Have a great day

Gg before

Gg today/after

One of the GSCs (others looked fine)

Banner that looks great still

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Quick update I read low humidity could cause leaf moisture loss so I put the humidifier in for a couple hours, lights are about to go off. It should bump it back to 40 plus but would 35 Rh cause that much? Last change was I put in the risers that are 2 inches but I’m still 30” plus from canopy of tallest plant which is that gg