seeds Using light during germination?

Just a quick question since I can't find a definite answer. I've read that you should keep seeds in complete darkness during germination, but why? I only have one heating mat and right now I have seedlings that are about to sprout their second set of leaves, seeds that have yet to germinate, and some that have germinated and currently are in a humidity dome. All different phases... Since the seedlings that need light are most important to me I have decided to keep the light on. I just want to make sure it's not going to affect the growth of my germinated seeds in the humidity dome. Thanks!

You definitely don't have to keep them in darkness. My germination setup is on a table that gets filtered sunlight from a nearby window. I think the more accurate thing would be to say light is not necessary until they sprout. Your setup is fine regardless of those stages. Keep the light on for your seedlings.
 
You might consider taking the humidity dome off and resort to more frequent misting for the seeds not yet germinated.