I just started some onions from seeds. They are just starting to sprout and need to go under the lights. Searching the internet some say 18 hours lights on, 8 hours off. Others say 12 on, 12 off for onions.

If you have started onion seeds under the lights for a number of years, I'd love to know your thoughts.
Thanks, Steve

What is the variety of Onion? Onions are finicky and the length of light is not the same for all of them.

I am starting Walla Walla Sweet, Sweet White Spanish, and Sweet Spanish Yellow Utah Jumbo. All long day for my Pacific Northwest garden.

Personally, I'm doing 12 hours of light. That's the general recommendation that I have found.

I have planted Amish Bottle Onion seeds in early June and they started bulbing shortly after the summer solstice. So I don't think you want to be using 18 hours of light.