Seedlings under heavy lighting test

So I've got a few hundred BCN critical cross Laos Highland seeds and I'm going to sacrifice a few in the name of boredom.

I see all these charts suggesting ludicrously low lighting intensity for germination and seedling stage...I have three seedlings that just germinated today and they are already under roughly 33000 lux (calibrated to 3000k) on an 18/6 schedule. Will be interesting to see how they go.


Let's put this rumour to test. I've heard 5-10k lux or less for germination and seedlings, but a single 11w household globe at 8" puts out twice that illumination and that just seems insanely low.

Watch me eat my words lol. After three or four days I'll raise them till it hits 50k lux and then keep going up until I see issues. Considering shade in my yard read 35k on a sunny day I'm not stressed at all.

For reference a single 11w 3000k led globe at 8". Just under 20k lux.

To get the "5-7k lux expert growers recommend" my single desk lamp shown would need to be around 12" away. When I see the seedling they showed under 6k lux, they were stretched as shit and struggling to stay upright.

VincenzioVonHook said:

For reference a single 11w 3000k led globe at 8". Just under 20k lux.
View attachment 5135179
To get the "5-7k lux expert growers recommend" my single desk lamp shown would need to be around 12" away. When I see the seedling they showed under 6k lux, they were stretched as shit and struggling to stay upright.

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FWIW, I sprouted a seed under a 600W SE HPS, and after the cotyledons were open, I put it outside. It's not growing fast because it's so cold, but it's under full sun 12+ hours per day.

It's fine.

GenericEnigma said:

FWIW, I sprouted a seed under a 600W SE HPS, and after the cotyledons were open, I put it outside. It's not growing fast because it's so cold, but it's under full sun 12+ hours per day.

It's fine.

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I've had the same results under a 320W quantum board at 20" full pelt and then outside after a week and a half. I'm mainly doing this out of pure boredom, and in response to Bruce B and his assertions that even cannabis seedlings can deal with high DLI. I'm gunna leave one under the lamp for a week or so (starting at 6k lux and then moving to 15k as recommended and see what the difference is).

I'd love to have somewhere that gets full sun all day. Most places I have grown have had 7ft fences and townhouses, leaving only 6 or so hours of direct light, if not less.

This is Gunna stay under the lamp for a week at 7k lux, this is the 11w bulb at 14" away as a comparison. I'll throw it in a 1 gal pot in a few days when it roots.

Nice side by side. I've never had luck with seedlings under high lux, but I'm curious to see how you do with this. Good luck!

Rurumo said:

Nice side by side. I've never had luck with seedlings under high lux, but I'm curious to see how you do with this. Good luck!

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Same. I just couldn't be bothered to set up a separate tent for seedlings at the moment so I figured I'd just chuck then in the main tent and see how we go. I'm guessing they will be a bit more compact, but all in all they can only generate so much energy from light to begin with.

It wouldn't be worth running a full pelt 240w board for seedlings by themself though. Just a waste of energy.

VincenzioVonHook said:

Same. I just couldn't be bothered to set up a separate tent for seedlings at the moment so I figured I'd just chuck then in the main tent and see how we go. I'm guessing they will be a bit more compact, but all in all they can only generate so much energy from light to begin with.

It wouldn't be worth running a full pelt 240w board for seedlings by themself though. Just a waste of energy.

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I've played around a lot with seedling light intensity using just my lux meter, but I'd love to do the same again once I get a par meter just so I have more accurate #s. I love these little experiments. 30k lux is usually my max during veg, so it will be cool to see how they do for you at that intensity, in case I need to grow some seedlings temporarily in my main tent at some point.

VincenzioVonHook said:

I've had the same results under a 320W quantum board at 20" full pelt and then outside after a week and a half. I'm mainly doing this out of pure boredom, and in response to Bruce B and his assertions that even cannabis seedlings can deal with high DLI. I'm gunna leave one under the lamp for a week or so (starting at 6k lux and then moving to 15k as recommended and see what the difference is).

I'd love to have somewhere that gets full sun all day. Most places I have grown have had 7ft fences and townhouses, leaving only 6 or so hours of direct light, if not less.

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Right on, hopefully we can all learn some stuff!

I may have sun, but not enough privacy. I only veg outside.

I think its less about whether you can/can't...more about whether it slows development or more particularly if you get reasonable internodal spacing. Sometimes you see plants that obviously have 2 or 3 or more good nodes but they're basically ground cover, which may make any kind of topping and training tough.

Rurumo said:

I've played around a lot with seedling light intensity using just my lux meter, but I'd love to do the same again once I get a par meter just so I have more accurate #s.....

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Your results would be essentially the same.

When Migro tested his Apogee Par meter against the Uni-T lux meter, the difference was only a few percent, more than enough accuracy for 99% of use cases.

Lux x .017 = PAR iirc

Billy the Mountain said:

Your results would be essentially the same.

When Migro tested his Apogee Par meter against the Uni-T lux meter, the difference was only a few percent, more than enough accuracy for 99% of use cases.

Lux x .017 = PAR iirc

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It was 8.8% difference on average (reading too high).

If you use the bluetooth version of the Uni-T it allows you to connect it to PPFD Meter app. Then in calibration settings you can change it to -9% (It doesn't do decimals). Pretty good accuracy for such a small outlay!

TrichDaddy said:

It was 8.8% difference on average (reading too high).

If you use the bluetooth version of the Uni-T it allows you to connect it to PPFD Meter app. Then in calibration settings you can change it to -9% (It doesn't do decimals). Pretty good accuracy for such a small outlay!

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I was ordered the Bluetooth model for that reason...I noticed the ppfd Meter app was around 18% higher than the apogee when I tested it using the phone sensor, and it varied depending on distance and spectrum selected. Sometimes it was worse, sometimes it was closer.

They sent me the wrong one. At least they refunded me. Should get off my ass and order the Bluetooth model. I hired an apogee a few times to gather readings at a few different distances to get a rough idea, but for pure excess I would love to purchase a PAR Meter.

The BT model and ppfd Meter is probably the closest I'll get though as I'm a student these days. Good times.

GenericEnigma said:

Right on, hopefully we can all learn some stuff!

I may have sun, but not enough privacy. I only veg outside.

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I grew four plants this size in my yard last year, in the middle of a townhouse complex lol.



The other two were also big sativas in the corner. See if you can spot them.



People's back doors are around 4m away from these pictured (you can just see them in the pic). It's illegal to smoke or grow in my state full stop here in Aus, and I have a few previous weed charges. At one stage they ended up a few foot over the 6ft fence and I had to constantly re tie them down.

I was in the only house in the complex, and was surrounded on all sides but people with only a few metres from the fence.

The police raided both neighbours over two weeks for smoking/being obnoxious drunk wankers and I was chilling at home with 4 monsters and two autoflowers in the yard. Was a hair raising experience. I could see the officers heads over the fence. If they rotated their heads a few degrees it would have been all over for me.

I've found if you keep to yourself and you help your neighbours, noone has a reason to be sour. There is zero way they didn't know I had multiple plants, two years in a row.

I miss that place. In uni accom now, and hiding smoking and growing so im stuck with a single 2x4 and a 1.6x.1.6 in the closet for drying

I can't see you having any troubles, before I had T5s I use to sprout seeds under a 250w mh i've also had 2-3wk seedlings under a 600w hps close enough to prevent excessive stretching.

I cant say for sure but from memory a seedling started under brighter light is ok one started under T5s then moved to bright light needs to be introduced slowly to avoid issues, I've a sp150 I occasionally used for seedlings without any problems.

It's been one day so far and the one in the cube already rooted out the bottom and side so i removed it from the cube into a 100mm starter pot. It's already three times the height of the others in less than 24 hours. Didn't expect that much of a difference, especially considering i put another cm or so of dirt around the stem and its still three times the height.


Will be interesting to see if there is detriment to having too close a node spacing. These are 50% Landrace sourced directly from Loas/50% BCN crit so they have long internode spacing naturally. These three seedlings are from the two larger crosses you see in the pics above.

Update. Week old. Not too much to report on as their hasn't been been much leaf to catch light.

The one under the lamp is now at 11000lux due to growing into the light, and the others still at the same. The one under the lamp is roughly three times the height and just popping its second set of leaves

The others in the tent have pushed out the second leaves and the third set it showing through.

I'd say it's going to make a difference moving forward now there's some leaf surface to accelerate the light differences. When comparing size, keep in mind that the one under the lamp is in a 100mm pot, and the others are in 140mm and 180mm pots.

I'll leave the ones in the tent at 35k lux and over the next week they should grow up to 40-45k lux, and the one under the lamp I'll rise to 15k lux tonight and see how we go. I'm going off the numerous charts that all suggest 5-7k lux for germ and first week seedling, 10-15k early veg and 45k late veg.

They will be vegged for four weeks before flip.

VincenzioVonHook said:

and a 1.6x.1.6 in the closet for drying

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Bro I got a 1.6x1.6ft tent too, lol. 50cm x 50cm. I thought I was the only one! It's my veg tent but I'm gonna upgrade one day. I love your escapades man. Can't believe you're growing in uni accommodation lmao. I just had my elderly parents visit for a few days. Ripped my tents down and hid my 5x vegging Blue Dreams under my house. Just got everything re-erected tonight. Hoping they didn't get too many nights of 12/12 natural light (I'm in North qld and it was 3 nights/dark periods). Any opinions on that?

To get slightly on topic, one of those blue dreams is amazingly stretchy and grew straight into my Mars ts1000 dimmed down a little. It got me thinking why do we screw around with ppfd/lux etc when at the end of the day it seems to come down to genetics?

Your seedlings look mega healthy though. Looking forward to how this goes. Cheers.

TrichDaddy said:

Bro I got a 1.6x1.6ft tent too, lol. 50cm x 50cm. I thought I was the only one! It's my veg tent but I'm gonna upgrade one day. I love your escapades man. Can't believe you're growing in uni accommodation lmao. I just had my elderly parents visit for a few days. Ripped my tents down and hid my 5x vegging Blue Dreams under my house. Just got everything re-erected tonight. Hoping they didn't get too many nights of 12/12 natural light (I'm in North qld and it was 3 nights/dark periods). Any opinions on that?

To get slightly on topic, one of those blue dreams is amazingly stretchy and grew straight into my Mars ts1000 dimmed down a little. It got me thinking why do we screw around with ppfd/lux etc when at the end of the day it seems to come down to genetics?

Your seedlings look mega healthy though. Looking forward to how this goes. Cheers.

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Yep, good old 50x50x100 for drying. I'd never seen them before either. Also have a 40x40x120 here which is handy for small autos. Its hectic here though. I think the running around behind backs makes it more exciting tbh lol. Everyone here is mega straight, young and foreign so they would freak out if they found out i'm mid 30's (they think I'm like 24) and growing let alone smoking. late bloomer when it comes to further study. Luckily due to the foreign nature, they are always cooking up nice food which permeates the whole building so smell is well masked if the smoke buddy and air purifier don't do the job.

The plants should be fine if it was only 3 days tbh. I've seen Blue dream autos stretch like shit as well. Mate had two NL autos and a blue dream auto in a 140x70x200cm. The NL were both 30ish" mid flower and the blue dream was two weeks behind and over 44". had one massively dominant cola. Made it hard to set lights for sure. The blue dream was 12" from the lights, and the others were close to 28" away.

Best of luck and hope you get an uninterrupted schedule from now on. luckily (or unluckily) I don;t have family up here so straight visitors are a non issue. If I do have someone over that doesn't smoke, i just chill in the common area.

I caved. The one under the lamp was stretching insane at 18k lux, so I put it in the tent with the others. Just seemed obvious it was going to be far less dense and far more leggy using the supposedly "correct" lighting intensity for indoor seedlings and early veg. Enough for me to conclude that the charts aren't always correct and bail. They are reg seeds, so I'd kick myself if the other two were male and the stunted/stretched plant ended up fem.

At day 9 it was basically toppling over with the slightest breeze. I have put it in a 1.3 gallon pot last night and buried 2" of the stem to give it a chance of staying upright without support.

Even after burying it another 2", it's still like three times the height of the others with far less leaf growth and no satellite growth.

Considering I only have a 120x60x150 I can't afford to have a leggy ass plant that has a long stretch period if it does end up being the only fem.

Sorry for concluding the experiment after like 9 days. Was far more apparent than I though it would be.