newbie gardening question

what temp can you germinate seeds at in a green house I herd 20c can you also germinate seeds at 15c or can you start them at 20c and tern the temp down to 15c

All I know about starting plants indoors to get ready for the spring planting is that the seeds will germinate at the cooler temps just like outside but if you keep the young sprouting shoots really warm even at nights then the plants will grow too tall too fast and be lanky with no real strength to their stalks. If you start them in your heated garage which is what i did it is important to have the nights cooler as it would be in their real environment outside. My younger brother is a horticulturalist and he told me that my problem with my seedlings was that they were not exposed to cooler nights which has the plant slow it's growth a little and helps them to have thicker stronger stalks thus making for a healthier stronger plant. Isn't it nice to have old farts like myself on these sites who have actually been around the block once or twice? O.K. maybe not but at least I am an old fart.

I never really thought about the temp thing, as I have never really worried about it. I actually do provide decreased night temps, but perhaps not enough. My lights are very close to the plants to reduce stretching, and the lights produce heat. My entire house Id thermostatically controlled to get cooler at night and the lights are on a timer. My plants don't stay under lights long. Just long enough to get a few true leaves, then they go out to the greenhouse.