Until they get near to pencil thickness, daylength will not be an issue. Leave the light on 24/7 so they get more light. Unless you have a very expensive professional lighting system, the light they are getting is very very low compared to sunlight. When they get a bit past pencil lead thickness, I would take them out side if it is warm enough during the day to get some real light. My favorite method is to take them out from dusk till dark the first day, and then put them out about 5 minutes earlier each day. Plants have the equivelent of gear ratios for accepting sunlight. It takes a week or two for them to change gears. To little when they are used to full sun, will stress them, to much when they are used to artifical light will often burn and kill them. Most onions can handle partial shade, at least in my area.

Negi,

Thank you VERY much for the information! I will certainly be able to leave the lights on 24/7. Hopefully, that will get them thick enough to transplant out by March 1st.

Lisa