Your problem isn't the light but the domes. Domes are NEVER left on after germination occurs. The combination of the trapped moisture and lack of air circulation is death to seedlings. Add the heat from the light and it is a wonder any survived.

HPS lights are great to use for seedlings but they do generate a great deal of heat so they are normally kept much further above the plants.

The formula for HPS light is watts= sq.' footprint. A 400 watt bulb gives you approx. a 4' sq. footprint of effective light - 4' wide, 4' long, and 4' high. Since this is a used fixture/bulb I assume then depending on age the footprint may have shrunk to 3' square. But it is seldom less than that unless the ambient temp in the area is quite cool. If that is the case you can lower the light more. I can't give you an exact height without knowing the age of the bulb and the ambient temps but I would never put one closer than 18" from the top of the plants.

Get the dome off, add a small fan to the area to keep the air circulating and adjust the light accordingly.

Dave

Thanks I think that I'll help a lot still use heating pads? And I just put all new seeds in yesterday so take the domes off still? Or wait for seedlings to pop up? Sorry so many questions but the window sill and direct sow or low flos I've used this is to much he said the bulbs about a yr but when I got it I assumed it was broke so I bought e at Home Depot but when I went to set it up to went on there in a niche in the garage so 66& up easy day add the light ok at night it drops to 60's.

Wait for the majority of the seedlings to pop up and then remove the dome. The rest of the seeds will follow shortly. Also remove them from the heat once most germinate. Heat, like domes is only used for germination.

60-65 is the ideal growing temps once the seeds are germinated.

If new bulb then no closer than 2.5 feet and on for 12-16 hours, off the rest of the time.

Dave

Thanks I'm gonna run with that thanks again

Sorry I'm posting a pic I'm getting spindle little sprouts that appear to be strectching and most rant coming up. I thought to much mositure with heat I added the fan as directed but nothing is coming out right I miss my flos I have numerous varieties in the same dome. As they pop I'm moving them over to an uncovered dome lower right of pic any more advice?