It's me again. Last year you folks told me I had leggy seedlings because I didn't have enough light. I figured I'd fix that--I wanted to get an LED setup but that didn't work out so I wound up with some 4' T5HO 6500K fluorescents, 4 bulbs/fixture, from the Jeff Bezos collection. After I took the domes off my trays, I swear I'm sunscalding my seedlings. Possible?

Yes it is possible. The dome lids can act as a reflector/magnifier and intensify the light. Remove the lids and create a little more distance between the plants and the lights until they recover. Once they are looking good or getting leggy then move them closer to the lights.

Even though your plants were leggy last year, I bet that they were fine once they were planted out. Life has a way of moving on...

I think you misunderstood, it was AFTER I removed the dome that I had the problem, although perhaps I was having it with the lids on, and it simply got much worse after I took them off.

Well it's up to you if the domes make it worse or better... The short answer is that you can burn plants with lights, so back em off and lighten up would be the simple solution. There's some kind of happy medium where the lights are the right distance and everybody gets enough light but not enough to burn... Just keep tweaking until you find that sweet spot.

I can't see too much light doing this.
The likely culprit is heat.
These light setups don't come close to putting out as much light as the sun.

Well, they certainly are hot, that's why I wanted to get LED.

Well there you go mystery solved.
Just bring the lights up a little as they are T5 and get some air circulation going.
The old rule of thumb with the T12 was just above touching.
Not so with the T5 banks.
I could keep 12 100 watt equivalent CFL Lights up around 10 inches without leggy plants.
They were in about a 10x10 inch grid.
Basically 1200 watts total in around 10 to 12 square feet.

Just in case people have different thoughts after seeing pics:
This forum is so easy to upload pictures to!

I would expect to see light-burns on the uppermost leaves. That's not what I see in your pics!

So what do you see?

I personally see heat problems.
But not the expert.

worth1 wrote: ↑Sat Apr 17, 2021 11:34 am Just bring the lights up a little as they are T5 and get some air circulation going.
The old rule of thumb with the T12 was just above touching.
Not so with the T5 banks.

I didn't realize the rule of thumb was different for the T5's, this year I decided to start my peas inside, and I cooked the first batch between the heat mat and the lights (I still had the heat mat on for the ones that hadn't come up yet). I didn't realize I was having the same problem with the tomatoes/peppers/basil etc. until some of them starting hitting the top of the dome and a lot of them didn't look right so I transplanted a number of them at that time, which was tough on them, and I backed off the lights some. But apparently I didn't back them off far enough. I have now turned off half the bulbs, we'll see how things go now.

This is only my second year doing this, and I already am planning to do things differently again next year, maybe LED lights, but definitely not going to start in these small cells, this didn't really work out the way I wanted it to.

T 5 lights are hot and you have 4 of them right next to each other
You would be far better off putting the two lights back in and backing off the distance to about 8 to 10 inches.
I looked through the posts again and didn't see what you had the distance set at to begin with.
Lower light intensity will not help at all but surely hurt.
To prove this take the fixture outside and shine it on something in bright daylight.
You won't see any effect on the surface you are shining it on.
The lumens of the sun is around 98,000 per square.meter.(LUX) at noon on a bright sunny day.
T5 lights don't even come close to this.
The T5 HO puts out around 5000 lumens.
Any light burn will be from UV light the sun emits until the plant grown inside gets use to it outside.
If sprouting outside it's just used to it from the beginning.
So the answer to your question too much light is no.

Fortunately I don't have to take any bulbs out, there is a switch for each ballast so I can turn them on/off in pairs. I have them about 7" away right now. I'm going to leave things the way they are for a day or 2 and see if things stabilize.

There are great set ups for purchase, and so many growers here have put a lot into their systems. But honestly, I've had such great success with the cheap 3200 lumen shop lights from Walmart (or any other box store). They are LED and put off next to no heat. I can put them as low as i want, and even have the leaves touch the LED strip with no damage to the plant.

It might not be the absolute best, but it's easy and cheap with nothing but success.

https://www.walmart.com/ip/Hyper-Tough ... src=aw.ds

There are larger and more intense versions was well. This is just the one they had in stock while i was at the store.

Thanks, Rockoe, but the easiest thing for me now is to get LED replacements for the T5HO's, rather than go to new fixtures. Next season.

Wow--those sure are cheap though!

Hey, I just realized, the other thing I'm doing differently than last year, is I'm watering with (softened) tap water, while last year I was using distilled water. I don't know if that explains anything.

The seedlings above obviously need more light. Now I only use led lights and I can increase the quantity of lumens without adding heat or using fans. A good way to find the right quantity of light is to take a batch of newborn seeds outside in the sunlight from 11 am to 5pm. With the right lighting you can have the same result.

I have a 8 bulb unit which produces some heat. I have an oscillating fan that blows away the heat as well as gently moves the tomato seedlings

Setec Astronomy wrote: ↑Sun Apr 18, 2021 12:49 pm Hey, I just realized, the other thing I'm doing differently than last year, is I'm watering with (softened) tap water, while last year I was using distilled water. I don't know if that explains anything.

I use unsoftened tap water to water all my seedlings. I never have used distilled water, I'd imagine some mineral content to the water isn't a bad thing, otherwise it may leach more out of the medium (same reason people shouldn't drink distilled water--but I don't know). Softened water will definitely have considerably more sodium than unsoftened, I'd switch to plain tap water, I wonder if they are getting too much sodium into the medium and that's throwing something in the plants off.