PAR vs. DLI for Autos

Ok, I’ve been using PAR as my light meter reading during my grows. Now I’m learning about DLI. So, does it really matter which measurement unit you should use? I just read this.

How much DLI do Autoflowers need?

“For Autoflowering plants the typical light cycle is 20 hours on and 4 hours off. This maximizes the time the lights are on while still allowing a few hours darkness for the plant to ‘sleep’ and metabolize. Because the day is longer the PAR intensity can be lower to reach the same maximum 40 DLI .”


Everything you need to know is discussed here. The formula given early in makes it easy to calculate how intense the light needs to be


Cannabis requires the same DLI whether it’s auto or photo.


Awesome. Intense but great info. I’ve been using Photone but only for PAR. So now it’s on to DLI. The chart is exactly what I was looking for. Thanks.

DLI is where it’s at. The Photone app will give you DLI instantly if it runs correctly on your phone. It makes setting the intensity and height of your lights so simple. From everything I’ve read optimal DLI for seedlings is 10-20, veg 20-40 and flower 40-65. You can run the lights at less intensity (lower PAR) for a longer period of time and get the same DLI as high intensity for a shorter time. DLI is a measure of total light over time.


I was about to make a post about this very question. I have read the original post about Dli and have been using the photone app for Dli. My question is, do we disregard wattage, ppfd, and lux and just focus on DLI? I can lower my lights and increase my DLI but what if my ppfd and etc are higher than supposed to be at that point? Or do they always equal themselves out ( if I get correct dli my other levels will be correct?)

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This is my first run indoors. From what I’ve read DLI is key. In my limited experience when I get the proper DLI the PAR is always in the suggested range as well. My ladies just entered veg (literally day 1) and are at 22 DLI. I’ll dial it up to 40 slowly.


I get why you said that but let me throw a monkey wrench into it.

I grow 12/12 from start to finish. I disagree that Autos don’t care about a light schedule. Because i am extremely consistent of getting 1 to 2 oz dried, cured and no stems.

I feel the 12/12 hurts Autos. I haven’t ran one at 18/6 but I am willing to bet I would get more of a haul if I did 18/6 for the whole grow.

Even my Indica Photos is between the same weight as my Autos and its extremely consistent.

Now Sativas is a whole different matter altogether. I get up to 2+ lbs per grow cycle.

For a caveat….these are different strains and the weight is consistent with Autos and Indicas of the same weight range. I could be wrong in logic but my experience has me leaning that 12/12 hurts Autos.


Couldn’t agree more. My autos have been on 18/6 since day one. I’ll probably try 20/4 and 24/0 some time, but I’ll never run autos anything under 18/6.


I’ve got nowhere near enough experience to argue that for a second.

As far as numbers and research goes it makes sense to me that if a plant can only take so much photosynthesis per day, that full is full. If it can be achieved with light over 18 hours, or more intense to match for 12 hours, that full would still be full.

I look forward to having the experience and perspective you have. :metal:


@Underthestairs I have killer lights so that is not an issue for me.

Example: I run HLG lights at full power.

With experience, you will gain a lot of insight. I used to believe Autos don’t care about light schedule and now I fully disagree. Because different strains still had the same weight as Autos and Indicas. Still learning about Indicas in full disclosure. My Sativas tho are legendary for a indoor grows

Now the pictures deals with Sativas. I have gorilla arms and Redwood Trees for legs… I’m 5’10” and I can reach up to about 7’4” high.

So the plant was cut in half and I had to pull the bottom half up so it didn’t touch the floor. Also a key point is the forest photo was not even 4 weeks into flowering.

At 6 weeks the front left plant Cola was a size of a volleyball and grew to the back right corner and she was also 2 feet out of the tent. This is the one I am holding.


So what’s your opinion on optimum light schedule for autos? I do 20/4 atm




Trust me, I’ve looked in on your grows. I’ve seen you pull more than one monster!

I also run HLG lights, but I’m still only on my second run with them. It has already become very clear to me that these things all have their own preferences for environment and training and such.

I look forward to having the practical experience too. Killer plants man!


Haha. I did bodybuilding throughout my 30s and 40s. I have weird genetics that caused my forearms to grow pretty big. One of the guys I used to work with said I had “Popeye arms” because my upper arms biceps and triceps didn’t keep up with my forearms.

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Thanks for this. I have charts and stuff but haven’t gotten myself honed in yet on the #s for each stage.

If this is the case why can’t we then just use PAR?

I run mine at 24/0 and get about 1.5 to 2.5 oz per plant. And, I’m a beginner who’s making mistakes and stressing plants. I’ve been thinking about 20/4 more for myself than the plants. Summer heat and humidity are extreme here – so 4 hours off from 2-6 p.m. would help immensely in keeping my grow room cooler with less effort.

But – I’m concerned about DLI v. PAR. I was taught to use PAR.

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You should change your handle to Popeye – great story.

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I just found this. Do you experts agree? It looks like it’s for 18 hours. So what happens to the DLI when you increase time to 20/4 or 24/0?

First three weeks:
The marijuana crop’s first stage is also it’s most important. Cultivators should ensure their first-stage canna plants get DLI from 13 – 19 units each day. That’s at a rate of 200 – 300 PPFD for eighteen hours.

At this range, there’s a chance of better yields when your cannabis plant crosses the vegetation stage.

Vegetative stage:
At the veg phase, your cannabis plant has to receive upwards of 20 moles of light each day. But the DLI isn’t expected to exceed 35 units during this period. Because this is a make-or-break stage, cannabis growers are mostly at odds on numerous fronts.

During the veg phase, canna plants usually require more energy to boost plant growth potential. Some indoor growers could flat-out disregard recommendations and double the required DLI for increased vegetation.

Several elements, like hours of light, light intensity, and grow light spread could impact plant growth at this stage.

Flowering stage:
Optimal flowering may require around 38 – 65 DLI units each day. If your marijuana flowers as it should, you can expect a good harvest.