What air temperature after germination?

What is the minimum temperature requirement to keep new seedlings outside in a heated greenhouse? I realize there is variability in the plant types, but all of my seeds had a recommended germination temperature of either 65 or 70 degrees. I have been heating the greenhouse to 55 degrees at night, but would love to lower the temperature to avoid the power bills while we have these cold nights. I am a total newcomer to growing anything, so I have read everything I could to get through this. I bought a home with an existing greenhouse last summer, so I decided to try my hand at the seed propogation. I got carried away and planted tons of seeds. The good news is that everything is coming up and looks great, but the bad news is that I don't have any indoor lights for the seedlings. If I have to, I'll get the indoor lighting, but if I can find out the minimum temp for the greenhouse I'm hoping I can do away with the indoor lighting and keep them in there after they sprout. Any and all advice would be appreciated!

Day temps should be approx 72°F and most night temps should be 55°F. And, it also depends on the plant varieties...some need to be warmer...around 65°F at night. Cooler variety type plants, such as pansies, snapdragons, petunias, dianthus, can take lower temps and do quite well. Also, keep in mind you should also have a fan or two blowing in the greenhouse - depending upon the size of your GH - to help circulate the air so you don't have warm areas, and this also helps to dry the plants after you've watered them. They're called HAF fans. Or Horizontal Air Flow fans.

The germination temps you mentioned above are soil temps for germination, not air temps. Day, night, and germination temps are different from each other. I use a heating pad I made up and believe I have soil cables that are set at 72°. I'll be taking pics of this later this year so folks can see how I went about this for my germination table.

As for indoor lighting, I only use the lights in my GH's for me to see when I'm in there. I have no need and don't see much of a need for any supplemental lighting unless you're growing specialty type crops. Bedding plants really don't need any and will do just fine with the normal day length lighting.