Did you harden them off? Or just put them outside and leave them? If the latter that’s the problem.

What I see in the pictures doesn't look like a months-old pepper plant. Peppers grow slowly, but not that slowly. If so, they've been seriously stressed. What are the "regular lights" in your grow area? But that's true. Sudden exposure to temps below 50F can be harmful.

It’s not just the temperature which is the problem if they are not hardened off. The plant tissue is too delicate to withstand sun and wind.

I think these ones were hardened for about a week or longer. Regular standard light bulbs and a few heat lamps. Then off 8 hours a day.

"Regular standard light bulbs" doesn't mean much. If incandescents, they're hot, and you'll never get them close enough to the plants. If LEDs, then a "100W equivalent"=17W LED is about 1700 lumens, which is barely adequate if one foot away from the plant. Takes a lot of light to be a substitute for sunlight!

3 heat lamps , 2 light bulbs. Not sure how much more I can add. they are bright. Not sun bright but very bright and are growing inside. Not sure how much more I can add or what can change.

Also have a fan on them to move them around.

Most of these were transplanted less then a week ago, that is why they are smaller.

The older ones I put outside in the past few days.

Those lights are not close or bright enough. They are growing rather weak, and lights are no substitute for hardening outside with the sun and wind.

I set pepper plants out in filtered sun or shade on warm days for a while, bring them in at night if cool. No direct sun at first, baby them at first, then more sun after a few days. I plant them then the first warm stretch. The direct sun can burn them at first, and the breeze helps build plant strength. Light rain if warm is okay.

You have a couple of "regular light bulbs" suspended several FEET above the plants? No way, Jose. Your plants are small and stunted because of lack of light. They are leggy, and the stems are very thin. If they survive outdoors, they may strengthen back up, but I'm not optimistic. If you want to grow seedlings indoors, you need to get some real lights. Even a T8 LED or fluorescent would work OK, if doubled, and put an inch or two above the plants. We're not talking about light that you can read by. We're talking about light that approximates sunlight. Very different things.

Temperature was my original concern, lights were second.

They are thin, noticed this from start after seedling. I moved some of the lights moved them closer and decreased any darker spots. and turned on the LED light on full. Fan is the only thing that is not on a timer. May have to transplant a few more of the starter ones soon.

How long is it suggested to harden?

Well, OK, but your picture isn't telling us the story you're telling us. The plants look like they are light-deprived. The picture is indicating light deprivation. For peppers, any temperature above 65F will be fine for seedlings. What was the temperature inside where they were growing? If it was cool, that could account for their small size, after months of growing. You said you hardened them for a week or longer. That's much more than they should need. A couple of days should be fine.

The temp was between 70 and 80 when they first were seedlings. Then eventually moved them to pots. I have a lot that need moved to pots yet, but was hoping to cycle them out as some harden.. Right now anything in my basement are around 70+ when lights are on and around 65 when they are off.

How and where exactly did you harden them off?

Basement. They are under the same lights as the picture. But now increased as suggested. (about double). They are in boxes with top open to contain heat and light. Off the floor about a foot. 16 hours lights plus lamps. 8 hours dark. Fan is running consistently (small fan)

OK. Hardening off, by definition, must take place outdoors. You can't do it inside. The purpose is to gradually get the plants used to outside conditions - sun, wind, temperature changes, rain .... You set the plants outside in a sheltered spot out of full sun for increasingly long periods until they're outside full time. Start with as little as an hour. Bring them back in each day when their time is up. Some reading: Hardening Off Pepper Plants - Moving Peppers Outdoors - Pepper Geek

Read through the link you provided and watched video. But one thing I missed, maybe just overlooked. Is it says 2 weeks total to harden them off, but do you bring them back into the grow area when you are in that process or just set them inside. Some of the pots are 3.5 gallon. I am also wondering if these in this next image are ok to start that process. These are still in my starter cups and was going to transplant them into large pots soon.

I’ve never used lights so I just bring them back inside.

I myself harden off for just a couple of days because here it's always pretty comfortable outside. As to sunlight, my indoor-raised seedlings never have any issue outdoors after being exposed to sunlight for a few hours for a couple of days. So people say two weeks, but maybe that's in case the outdoors look like serious abuse.

But you really need to do something about lighting in your seedling grow area. No question that plants that have been starved of light aren't going to take kindly to being shoved out into full sunlight. You have a lot of pots, so adequate indoor lighting isn't going to be that cheap. You might consider putting them outside in that box with a protective piece of transparent plastic over the top, just to get real illumination. As long as the air temperature doesn't get below 50F, they'll do OK. Maybe a heat mat underneath?

I brought most of those damaged ones in, some looked like they would be ok .

I did bump the lighting a lot. and see that the plants are appreciating it , even after a day.

One thing I did on the ones on my deck is just toss them outside because I thought they would be ok. Now any plants I put outside I am going to condition and pay attention more to how they are doing. There is a few with broken stems, those probably wont make it.

Yes, I think two weeks is erring on the side of extreme caution.