Impatiens are pretty slow to germinate...like 14-21 days. Your soil temperature should be about right but you don't want to go any warmer. Yes, light is recommended for germination and the seed should not be covered with potting mix.

Only thing is that the soil underneath the surface could have dried out in that amount of time. That's one reason why misting isn't the best way to moisten. Try bottom watering the trays.

Dave

Dave, I don't typically water my containers from underneath until I get a set of leaves. Since the impatien seeds are on the surface of the soil (or just slightly beneath) I would think that a generous spraying (not misting) every 3-4 days keeps the soil surrounding the seeds pretty moist.

That's fine as long as your mix was wet enough to begin with. But over a period of several days of that soil "sweating' out all its humidity it could be quite dry. And with peat based mixes that means water-repellent. In that case seeds can germinate - sprout their initial rootlet - and then almost immediately die as that emerging rootlet seeks moisture where little to none exists.

Misting is very superficial, just the surface of the mix, and evaporates quickly. Can happen within hours. So with slow-to-germinate seeds deeper moisture is vital. With no signs of germination one often discovers they did in fact sprout but then died.

Dave