From: "FDR"

When starting seed, like tomato or pepper plants, is it necessary to have a
light on before the seed has sprouted? I plan on using a heat mat for the
first time this year, so the warmth of light won't be needed, but I wonder
if it's still necessary to have light

Not much in the way of light is needed before seeds sprout but lots of light is
needed once they have sprouted plus cooler temps. While an ambient temp of 75+-
is good for sprouting about 68-70 will be better for growing.