Once the weather starts to warm up a bit the pepper plants can benefit from being outside during the day. This allows them to get the much brighter sun light and frees up space under the fluorescent lights which has probably gotten quite crowded by now.
“Outside During the Day” does not mean outside at night. It’s still way too cold at night. Further down on this page are the guidelines as to when its OK to leave plants out all night.
Plants must be allowed to gradually adjust to the much brighter sunlight. If this is not done the plants will be severely sunburned, which will stunt their growth or even kill them. Worse, the damage caused by sunburn does not exhibit any symptoms for a couple days – by then it is too late. Don’t slack off here – this can be a precarious step and result in disaster if your not careful.
The amount of time required for the hardening off period depends on the difference in light intensity between your artificial light and full sunlight. If your artificial light setup is on the skimpy side then take more time to harden them off.
Also, when moving outdoors there may may wind and heavy rain exposure which can be equally damaging to your up_to_now pampered seedlings. Be sure to provide protection from severe rain and even light winds while hardening off. For rain use a cold frame, or delay hardening off for better weather. For wind, use natural (or erect your own) wind barriers. Plants left flat on the ground suffer less wind damage than those placed up at waist level on a table.
In preparation for hardening off I increase the light from my fluorescent fixtures up to 24 hours per day several days in advance of hardening off. I’m just getting them ready for lots of light. Some balk at this, thinking that light/dark ratios affect flowering and fruiting, but my experience does not support this contention. Many plants are day length sensitive and use the shorter days in the fall to start producing seed for next years crop. If you think about it, this doesn’t make sense for peppers which originated near the equator where day length is pretty much constant all year. Peppers in their native habitat are perennials, and flower/fruit all year long.