there are many exceptions depending of species BUT yes as a general rule use lights 16 hours a day & heat mat untill seed germinate then remove from mat.

In past years I did the 16 hrs. a day but I forgot to turn them off this year and varieties of seed I have sowed in the past came up sooner.

It's according to what you're germinating, in my opinion. I only do vegetables, and always germinate mine without light. As soon as the tiny seedlings emerge from the soil, I hit them with 16 hrs of light each day. I don't use heat mats....

EG

Here is a link that might be useful: EG's garden blog

I agree with engineeredgarden. Unless the seeds specifically need light to germinate, you are wasting the electricity keeping the lights on at all until you have germinations. Once you have germinations, then the lights are required.

And some flower seeds require darkness to germinate. Vegetables don't need the light but might benefit from the extra heat the lights generate if you are willing to pay the bill for the electricity - I'm not. ;)

Dave

After germination, how important is having heat? Is there any danger of putting the seedlings outside above freezing temps?

After germination heat should be reduced and water monitored carefully. Unneeded heat and excess water create the condition favoring damping off disease. Good air circulation is also a must at this time. Al