So last year I grew Orange New Guinea Impatiens. I tried to germinate 25 seeds. I was only successful growing 10 plants. I just could not get them to germinate. But thinking back on that process, I had them in the germination tray but also on the heating mat. And to aid with germination, impatiens need light. But with the light on 24/7, I had soil temps above 80 degrees.
This year I am not using the heat mat. I have a clamp light about 8 inches above the tray and I've got my maximum temp setting at 77 degrees. The light alone is capable of keeping the tray 75 to 77 degrees as it cycles on and off. I put 100 seeds in the germination tray on March 1st and I've covered them with a piece of ziplock bag. I will keep you posted on their progress. I think the seeds are starting to swell a bit but no sign of radicles yet.