Another help with stretching seedlings is to take a frosted plastic cup with holes in it and put over your seedling. You need to increase the light, of course, but it creates a Lighting tent effect which brings in light from all angles rather than the plant reaching vertically for light. Just a suggestion I use
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I would use a clearer solo cup…that one’s a little opaque and has a hole in it. Lighting distance and intensity is the culprit behind stretching. Lower the light and adjust the intensity(DLI of 18-23). The solo cup provides the needed humidity of 65-75% needed to feed the seedlings, they’ll absorb the moisture through their leaves 
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Frosted plastic cups cause the distance to the light to be inconsequential as the light passes through the sides and the top, to create an envelope of light rather than a spotlight. The same principle is used to photograph objects that require very even lighting from the sides as well as the top Most jewelry, photography, and small product photography is done Commercially is done through the use of a Muslim tent with the same light dispersion idea.
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Can you please post link(s) to the supporting research that leads to these conclusions?
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50 years of commercial photography. The study of light and shadow using sophisticated light meters from all angles throughout the majority of my professional career.
If you take an incandescent light meter and utilizing a dome sensor, you can remove the frosted cup And see that the light ratio is substantially greater pointing vertically, than horizontally. However, when you create a “tent“ the light intensity evens out substantially, and if done properly equally. Give it a try on your next seedlings and you can give me the scientific data. Make sure that you do have vent holes in the cup.
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How does a vent hole help? iirc the point of a dome is to trap humidity.
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The point of the frosted dome is not so much for humidity as it is for even like distribution, which reduces the stretching effect that seedlings incurred when trying to get two more intense light. Even if you’re wanting increased humidity, some fresh air is a good thing. But I will reiterate the frosted dome is to help prevent overly stretchy necks.
The recommended 300 minimum PPFD for seedlings is sufficient to prevent stretching.
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Sorry, but this sounds completely unnecessary to avoid stretching, and most likely counterproductive.
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My concern is that we have dozens of first time growers here. It would be unfortunate if they were led to believe that they can address inadequate lighting with tricks.
If a grower doesn’t have enough light to prevent a seedling from stretching, then the grower has no hope of ever flowering a plant successfully. If there is a problem with lighting, then it is the light itself that needs to be addressed.
I agree. If you are going to run a humidity dome, then run a humidity dome. Cutting a hole in the dome defeats the purpose of a dome. A dome with a hole in it won’t be able to retain humidity.
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Lighting tents are no gimmick or trick. It is just a way of evening out your light source. It’s been used for 100 years in photography and it certainly does not cause a problem. I agree that if you have the exact perfect lighting you won’t have as much stretching, but it’s still a problem that is easily helped with an eight. Cent , but it’s still a problem that is easily helped with an eight cent frosted cup if you don’t think it is a good thing don’t use it. As far as the first time grow or if you were around back in the early 60s, you might be able to say that about me. I was probably growing cannabis before you had pimples there are a number of things that can assist stretching necks and they do occur even with proper lighting depending on the strain I refer you to the ILGM growers Bible
And as far as enough light for flowering, who in the world starts their seedlings under flowering lights? I have separate seedling, clone veg, and flowering light situations. The dome system, however, would allow you to put your ceiling under your regular veg, light, cutting down the intensity enough for the tender young plants, and not giving them too much of a direction to stretch too. I’m done with this. It was just a situation that might help some people and if it helps him great. If it doesn’t help you don’t worry about it.
All due respect for your photography background and lighting experience, your seedlings are not photo subjects unless you happen to be taking a picture of them, they’re live plants.
As far as your angry response regarding age and pimples, you’re not the only grower here who isn’t a teenager. Most of us are adults and capable of productive back and forth dialog without anger or insults.
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I’m going to pile on this one. The member’s own early posts directly refute his experience claims.
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Because I took about 10 years off and realize things have changed different ways of handling different things and I’m not too proud to question everything don’t make assumptions. As I said, if the frosted cup idea helps you great if not forget about it do you have so little to do that you have to pursue something that you don’t think and help you. This is becoming personal, and that is not a good thing. Even the Bible says when you contend with a fool you become as a fool. I’m done with you.
I agree. Speaking of getting personal; I’m not sure how you might expect that implying that @Cap_Ron and I are ignorant children would go well for you, but here we are.
We don’t do bro science here and members will nip it in the bud pretty quickly. It is why I asked you for supporting research.
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Take any type of a light meter and see if the diffusion that I’m talking about is not valid. In photography we have been doing it for decades diffusion discs, Gary Fong diffusers the diffusers that Nikon, Canon, and other light manufactures sell or for the same purpose relates to horticulture as well, if you defuse the light and it comes from all directions or Omni directional, the plant does not struggle towards One light Direction. Gravity plays a big part in the seedling knowing which way is up and down. But common sense will tell you an envelope in light disguises the direction of light. As I said, if you want to try this and if it helps you great and if you don’t leave it alone, but common sense will tell you diffusing the light source makes it less directional if you need scientific proof for that I don’t know what to tell you it is so blatantly obvious Now scientifically how much it confuses the plants direction of growth you’re correct I don’t know but if you don’t think it helps don’t do it and don’t worry about it. I just made a suggestion and comment why you can’t either accept it or ignore it is beyond me. I’ll tell you what do me a favor and just ignore it my comment and everything else because how well or poorly you do actually doesn’t mean a thing to me. It does work though
I am not saying that you are incorrect about the diffusion. I am saying that it doesn’t matter and that such a method creates more problems than it solves. It is simply bad advice and has been addressed as such. If new growers ask about stretching seedlings, the growers should (and always are) told to increase lighting intensity. Your diffusion argument is valid, but it is not relevant. There are better, more appropriate, more reliable ways to address the problem that doesn’t create other problems along the way.
We do our best to ensure that the newer growers have good information that will help their grows. Your idea conflicts with the frequently recommended concept of a humidity dome. It also conflicts with the concept of providing adequate lighting.
If you have to lie about your experience and resort to name-calling to make a point, then you probably don’t have a good argument.
Good. I am muting the thread as I am done with it too after having been referred to as an ignorant child. You have a good day.
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I’ve had simular issues with my seedlings. Too much light,too little, too close, too far etc. Solved it by getting a HLG 65 fairly inexpencive and perfect for seedlings. Better node spaceing no streching just right. I leave it on till a week after transplant they drop the big light in. Seems to me to be “the right tool for the right job”
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When I was a young tyke used to go to my grandparents house I would see cups just like that in his “room” he had a couple stakes of them would peek in there when he left door open and would always get caught by gram and put in time out lol