Answer: Impatiens seed is very sensitive to storage conditions and can be difficult to start. It requires a warm soil, but temperatures over about 85 degrees can inhibit germination. They should be pressed into the mix rather than covered with soil, then covered with plastic wrap to maintain humidity. The pot should be placed in a bright location but out of direct sunlight because the plastic causes rapid heating of the contents. (Exception: apparently the Accent series prefers two days of darkness).
The marigolds on the other hand are much more forgiving. Started as you described in a slightly damp but not soggy soil, lightly covered and misted to ensure good soil contact, they should germinate within 3 days to a week at soil temperatures of 75 to 80 degrees, longer in cooler soil. Remember that the soil temperature is cooler than the ambiant room temperature; this is why many gardeners will use a source of bottom heat to help germinate seeds quickly or to accommodate the seeds requiring warm soil.
Finally, the lights are not needed until the seeds germinate. At that point, (most seeds germinate withon a few days of each other, so when about a third have sprouted) remove the plastic cover and set the plants under the lights with the lights only two or three inches above the plants.
Good luck with your seeds!
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