Ppfd vs Dli with light movers

If you run your stationary light at 1000 ppfd for 12 hours you get a dli of 43.2

If you run your light on a light rail (moves 1 light over 2 plants) at 2000 ppfd for 6 hours (the amount of time that the light is directly above each of the 2 plants) you get the same dli of 43.2

So you should get the same amount of yeild correct? What am i missing?

Photon saturation and efficiency.
2000ppfd will not be used at the same efficiency that 1000ppfd would be. Well into diminishing returns even at high CO2 levels.

But conceptually yes, 43.2DLI is 43.2DLI. Being that carbon fixation is quantifiable via photon count, DLI is your total available photons and max possible carbon fixation.

Could also have morphological effects from shorter photoperiod.
Also, hard for me to conceptualize a light mover going from 2000ppfd to 0. It's more of a intense(2000ppfd) to less intense(maybe 500)ppfd thing. Not completely on and off.

i agree, unless you block the light out compleatly to darkness, you will still get light on your plant that the light is not above. your only talking two plants, if it were a row like 10 plants (light movers were used to run the length of ten plants, a pack of seeds) thats going back about 40 yrs that info ,when i first started growing
with only the 2 plants, i wouldent worry

2000µmol is, arguably, out of the question. The light saturation point for cannabis, in ambient CO2, is 800-1000µmol. If you're using CO2, you can crank it up to very high levels (1500+) so your plants could use 2000µmol but, per the graphic below from the Chandra paper, net photosynthesis plummets when PPFD > 1500µmol.



Those are the specifics for your example. In general, yes, there's no argument that, as long as light is the limiting factor in your grow, more light is better.

Going to the concept behind your "which is better" question - as long as you don't exceed the light saturation point, it's probably a moot point but most growers don't veg cannabis at 24/0 preferring 18/6 or 20/4.

The bigger issue, to me, is to get your plants to the light saturation point as quickly as possible and keep them there. More light results in a larger, higher quality crop.

You also need to invest in very powerful lights that are turned off half the time (assuming that 12 h is the max photoperiod possible). Results would be interesting from an academic standpoint though. Very high light levels are better taken as long as DLI stays reasonable.

I dont see the point of the light mover though. That helps to compensate for uneven spread, especially by point source lighting. With quantum boards or bar lights it has little benefit.

RCJR said:

If you run your stationary light at 1000 ppfd for 12 hours you get a dli of 43.2

If you run your light on a light rail (moves 1 light over 2 plants) at 2000 ppfd for 6 hours (the amount of time that the light is directly above each of the 2 plants) you get the same dli of 43.2

So you should get the same amount of yeild correct? What am i missing?

Click to expand...

No, not really.
Light mover doesnt move instantaneously from one plant to the other. It wont hit each plant with 2000ppfd for more than the instant it takes for the mover to "turn" from one direction to the other.
In order to get the situation that your numbers are talking about youd need one 2000ppfs light hanging over each plant, alternating on and off.

If i remember correct with co2 max she can take is 1500.soo probably you are wasting most of the light

So im limited from my electrical pre wired in this room. These 4 lights and dehumidifier is all i can have without overload. So i can't add any more lights. So i went with the 2 light rails to squeeze 8 large plants under these 4 lights. My goal is maximize these lights on the rails to get the most yeild as possible. These girls have been under this setup for 3 weeks and seem fine under 2000 ppfd with the dli at 43. Looking for input.

How much power goes to your dehueys?
What make and model are they?
We are in a similar situation part of the year and use quest dehueys with a separate external control circuit. Our plan is to setup an automation setup with humistat which switches the dehuey on while dimming some of our led drivers to 0 while humidity is too high. That way you can use the amps of the dehuey for light when the dehuey is not used. The way were set up with diy lights this isnt very hard to setup, infact we can do it with nothing more than wifi/intelligent relays, no computer needed. But if you have bought lights this may be a bit more involved with programming and swtting up a computer and arduino.

amneziaHaze said:

If i remember correct with co2 max she can take is 1500.soo probably you are wasting most of the light

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These plants can definitely take more than 1500ppfd with CO2 supplementation. Most people touting that number have never grown at those light levels, and reference studies that are highly outdated. Fluence did a study showing cannabis yield increases up to 2500ppfd before photoinhibition set in.
If people’s plants can’t take 1500ppfd, that’s a grower problem, not the plant’s problem.

Ok. So you have light already. Which all have a PPF output...which is your maximum amount of carbon fixation, no matter how you move them. The light will not output more than their PPF, no matter what your instantaneous spot PPFD is.
The light movers allow you to take the hot spot that may be over saturated(say 1500ppfd when not moving), and even it out with the outer edges that were possibly understantuated.

@amneziaHaze @Rocket Soul @Lou66 @Delps8 @go go kid
I posted pics of my setup above

RCJR said:

@amneziaHaze @Rocket Soul @Lou66 @Delps8 @go go kid
I posted pics of my setup above

Click to expand...

Scorpion over one plant at full power seems like overkill to me, they give a 5x5 foot print and those plants look to have a smaller cannopy then 5feet. How hard are you running those lights? How much do you yield per plant? A scorpion like that on full power should yield about 2.5-3 pounds, is that what youre getting per 2 plants?

RCJR said:

So im limited from my electrical pre wired in this room. These 4 lights and dehumidifier is all i can have without overload. So i can't add any more lights. So i went with the 2 light rails to squeeze 8 large plants under these 4 lights. My goal is maximize these lights on the rails to get the most yeild as possible. These girls have been under this setup for 3 weeks and seem fine under 2000 ppfd with the dli at 43. Looking for input. View attachment 5368609View attachment 5368610View attachment 5368611

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Very nice set up!

My response to your posting included "arguably" because, in very high CO2 and a good grow environment, a grower could you 2k µmol.

And that's your set up!

If you want to maximize yield, "turn it up to 11". Cannabis is a light whore loves light.

43 DLI is…mid-veg for me. If you want maximum yield, you're not going to get if from 43 mol.

(BTW, how are you measuring PPFD? Seeing that you're at 43 DLI and reporting very high PPFD's, I'm getting this icky feeling that you're using Photone. If so, dump it and get a meter. If you're inclined, the Apogee is nice but a Uni-T lux meter will do just fine.)

I run in ambient CO2 and my lighting protocol is to get my plants to the light saturation point as quickly as possible. I usually measure PPFD daily, using an Apogee MQ-500 and I sample in multiple points, up to 24 when the plant fills the tent (2' x 4'). Here's my lighting data from yesterday.
It's a Growcraft X3 running at 283 watts (hang height is about 12"). Cols 2 and 3 are PPFD and DLI (the photoperiod is 24/0). 72 is the standard deviation of the PPFD and the SD for DLI is 6 so it's a fairly even light cast. The average DLI on the plant is 82 with some spots as high as 88.
The res is at 500/500 PPM.



At these light levels, there are no signs of stress and the plant is showing excellent growth.

[time passes]

My grow journal from when DLI was 43±. That was on day 22 of the grow. As you can see, I went to 51mol the next day. Cannabis loves light.


I've attached the Chandra paper which is considered the seminal paper on growing cannabis in ambient CO2. Bruce Bugbee has stated that 1200PPM (CO2) and 1200 µmol is the sweet spot but if I were growing using CO2, I'd be inclined to follow the Chandra paper.

Note that the discussion in Chandra is re. net photosynthesis ("net P") while the other paper shows that crop quality and yield increased in an almost linear manner as PPFD (DLI) increases. At 43 mol, you'll get a decent crop; at 80 mol, you'll get at least 50% more.