I would think that its shortly after they pop through the soil - the seem to grow towards the light even at the cotyledon stage...

Though they may not use it for more than warmth until the true leaves pop up... I'm not sure...

The cotyledon of peppers do the same for the seedlings as true leaves, guess they are the forerunners until the true leaves appear then either stay or eventually die later. I always put under lights as soon as they sprout. I had some sprout and grow yellow until I placed under lights which they then turned green in a matter of hours.

OK, I have been running my lights since a day after they started sprouting just to be sure. Does kind of sound like they expect light right after they pop up.
Bruce

Sounds good, I have my lights inches from the seedlings keeps them short and compact instead of long and leggy, floro lights of course or would not be so close. I raise as they grow, and from your other posts sounds like you got it covered with making hight adjustments easy. How close do you have yours?

Mine are within an inch of my seedlings. The tallest ones are a bit closer right now.
Bruce

I think I just got my answer to my original question: When do peppers need light?

I checked on my seedlings just a minute ago after the lights had been on them since 2am last night. It was about 1pm when I checked them so about 11 hours. Well, what I immediately noticed was that all the seedlings in the outside containers were leaning slightly inward toward the middle of the two shop lights. This was with the outmost bulb on each edge directly above the those same peppers. They were leaning in even with a 40W floro less than an inch directly above them, so my theory is that they are already looking for as much light as they can get even with just the Cotyledon leaves right now.
Makes me wonder if I should get a third bank of lights set up already. The two banks are already only about a half inch apart but still cover the seedlings on both edges.
I had problems with "leggy" plants last year. I dont want them growing legs this year too.

Bruce

My lights are set on a timer for 18 hour days and set within 2 inches from the tops of the peppers when they sprout. As they grow the lights move up..... When some get taller than others (varities grow differently), I sort them out and the taller move to their own tray and lights..... A lot of musical pepper pots moving sometimes, but they grow nice beefy stalks and strong all around by the time they move to the greenhouse.

Sounds like a nice setup sandy. I'd never be able to keep them straight though. I know what my plants are based upon where in the jiffy greenhouse they are. Even drew up a map.

If I were to start moving them around, I'd likely lose track worse than I have on some already (first batch started in oct, when I planted them in cups, I was going to do the same and leave the cups sorted by pepper type. Well... Lets just say I had a helper, and now I have about 140 unknown plants.

There after, I've been a lot more particular with making sure the names are clearly written, and also have not asked for help from that person again xD

Yes, they need light right away. If you want to reduce the internode length, use 6500K T5HO's. The brightness and temperature of these lights keeps them from stretching. LED with a high amount of blue will do the same.