Light recommendations cook my Autoflowers!

It’s not just due to the light (I was having issues where the root ball wasn’t getting enough water due to using fabric pots)…

But just the same, Mars Hydro’s recommendations cook my plants. Others have said for autoflowers to keep the light 24" above and set it for 100%. That would be the same as setting it at 50% and having it 12" away, wouldn’t it? That would definitely cook plants, maybe even in flower.

THAT WAS BEFORE… This time… I’m being really careful. I just set the light for 50% today. It had been at 43% prior to that for quite some time, yet I was still seeing light damage on leaf tips (and some “praying”). I had been keeping it at about 20" and shooting for about 400 par.

Now that they’re both fully in flower, I was thinking it’s time to head toward 600 par, but if I am already seeing tender leaves…

That’s my whine. Here is the info, followed by pics.

Mars Hydro SP 3000 (I had better luck with previous TS1000…)

Left: Girl Scout Cookies Extreme, flowered REALLY late and is gigantic
Right: AK-47, flowered early and is small for a 7 gallon pot but looking pretty good–some leaf tip damage from too much light, I think
Approx. 9 weeks old each (including veg)

Autoflower supersoil mix, tap water, tap is about 6.5 pH, water every 3 days (about one gallon each, but obv Cookie needs more water than AK); still add cal-mag, occasionally some bud bread or kelp juice

Can’t remember what else you need to know. It’s about 75F, and the humidity is always 40-50%, but I shoot for about 45%.

Best plants I’ve ever raised, believe it or not, because I realized I need to let them soak up the run off, and because I realized that prior to this THE DANG LIGHT WAS COOKING MY PLANTS! If a person uses the Mars Hydro recommendations, they will absolutely incinerate an autoflower. I don’t get why more people aren’t having this disaster.

Photos are meant to show that even with my conservative (I thought) lighting, damage is still occurring

I’m not sure what I need help with… I guess wondering if anyone else has had these issues and why there aren’t stern warnings for autoflower growers not to use photoperiod light settings (i.e. you need less par for autoflowers).

AK-47 with previously damaged leaftips

full view (Cookie on left)


Cookie with damaged leaf tips and lighter-green and yellowing leaves


I have never treated an Auto any different than a photo period.
Where did you hear that?


Dang I can’t edit anymore. The plants are about 9 weeks old (including veg).

Photos and Autos | The Recommended PAR levels for Photos and Autos - MIGROLIGHT.

That’s not where I first read about it. But my plants were all getting cooked, and I couldn’t figure out why.

Additionally, autoflowers have a light cycle where they spend a lot more time in the “sun”. Therefore the sun needs to be weaker. 12/12 is a totally different deal from the 20/4 that most autoflowers get.

Lux/ppfd/DLI chart for Autos? | The Autoflower Network This link had a little chart…
Lux_ppfd_DLI 24hr CT4000

In this example chart, the highest par it ever reaches is 555. This would be like setting a Mars Hydro SP3000 to about 55% and keeping it at least 19.5" away. So a full 100% at 12", even in flower, would be absurd. A plant can’t even use that much light indoors without some kind of crazy co2 setup.

1 Like

Looks to me like nitrogen toxicity not light burn dark green waxy leaves and burnt leaf tips all point to too much nitrogen


Light intensity and distance are not a linear relationship. Intensity changes with the square of distance. So twice as high is one quarter the intensity. 100% at 24” and 25% at 12” are equivalent.


But they’re not waxy… they’re not turning into claws either.

Yikes okay… that’s good to know. Either way, my numbers for 19.5" should be correct. I think. Conveniently, it should be about the same as the % setting (i.e. 40% is 400 par).

I have grown autos and photos together several times With same everything. Overall plants look good. I don’t see any light burn. Welcome back good luck !


I have been giving my autos 50 - 60 DLI since they got established. I have 480 watts in the tent. Nobody roasted yet, and Temps hang out below 80.

I don’t check light height, just make sure they are within the DLI range.


Yeah if can download photone app it will help give u an idea of your DLI, from my understanding you can give to much light that might produce some foxtailing but if that’s the case just either turn down light intensity or raise your light


Thanks, guys–I’ll see if Photone works for me. My phone is really old

1 Like

can’t edit!

Photone–it seems really inaccurate and is now telling me I need a “diffuser”. I did not purchase the LED mode, though, so maybe that’s why.

Yes on older phones you need to make a diffuser not hard just need printer paper

I can give it a shot! Will it still work without me buying LED mode? Or maybe I should buy LED mode.

Best results from thse that tested against Apogee meters was using the sunlight mode. iOS phones need a diffuser, androids do not. Follow instructions on how to make one, but it’s a strip of printer paper wrapped around the lens and taped to the back.

Okay, great!! I’m on iphone, but sounds like I can just use sunlight mode if I use a diffuser

Correct. You may have to buy sunlight mode, btw. To get an accurate read on DLI you have to set the hours of light you’re using. I forget what the default is, but it will give you an incorrect DLI if you’re running something different.

The burnt tips is just slight nute burn. Backoff nutes a tad b4 you worry about the light. Flowering with the SP3000 and autos, on a 18/6 light schedule, you want to be around the 16" range above canopy. This should put you in the 55-60 dli range


No difference in photo or auto light requirements. I run photo together with auto. If i decide to flip photo in auto tent i change light. Auto just plugs on along. I would look for other issues before light. I run up to 3 550r in my 4x8. Watch the girls. They will “glow” when feeding good on light. Will be very vibrant. Just adjust a little each day till you see them react. They will.

1 Like

I don’t know how it could be nute burn. The nutes are all in the soil. I don’t put much in the water except cal-mag.

Forgot to mention, I do the typical 20/4 autoflower light cycle, not 18/6. 16" above the canopy at 100%? Not sure what it would be for 16", but that would be 1240 par at 18" or 940 at 24". That’s a lot. I don’t think autoflowers can even use above 700 unless there’s a co2 setup.

1 Like