Seedlings need 14-16 hours of light every single day, without fail. Don't leave them on for 24 hours a day though. Like us, they need to rest at night. So plan to keep your artificial lights on for 14-16 hours during the daytime, and turn them off overnight.

Should seedlings get 24 hours of light?

In general, seedlings should receive roughly 14 to 16 hours of light a day when situated in a south-facing window. ... Many people make the mistake of leaving their seedlings under fluorescent lighting 24 hours a day. This does not make them grow faster, and can actually hinder the success of your seedlings.

How long should seedlings be under a grow light?

Once sprouted, most vegetable seedlings and other garden plants require at least 12 hours of good light per day, along with 8 hours of darkness. However, they'll grow the best with around 16 to 18 hours of light. Houseplants are happy with less, where 6 to 12 of light is sufficient (depending on the type of plant).