I start them on a heat mat without lights and then move individual plants to trays under lights as soon as they come up--leaving the ungerminated on the heat mat.

Wait until signs of growth unless the lighting is being used for a heat source. I always start mine on top of the freezer and when about 50% are just peeping out fire up the lights.

Thanks guys. That answers my question.
John

I have two heat mats and set them up under my lights. My problem is that I grow in my cellar, and the temps down there are in the low 50s. I start my seeds in coffee filters on a heating mat and transplant sprouts to 9-cell packs.

I move seedlings to 9oz plastic cups, and hopefully that holds them until it is time to plant them out. Though the more precocious ones get upsized again to 18oz cups.

can the seeds be in cells when they are atop of the freezer or do they need to be in something else like coffe filters?

I use small newspaper rolls (about 3cm) with up to three seeds (1 variety) and have them in a heated propagator. As soon as they germinate and start unfolding their first leaves, I take out the individual roll and place them under the lights. There I let them get their artificial sun and after some time I pinch out the worst ones (keep one or two - when two transplant them both to bigger containers later on).
It is much more convenient to be able to let all the ungerminated in the propagator and move only those that started ok, so individually transportable small containers are best for me.

So heating first, and lighting second (they need the leaves to take in the light so ...)

Now that I've potted up most of my pepper seedlings and started tomatoes in the 72 cell starter trays I'm running out of space under my lights. I will have to move the larger pepper seedlings to window sills. Hope they don't get too leggy before I plant in mid-May!
John A

Get another set of lights--unless you have REALLY good light from that window.