At about midnight I went out to check on the chicks before going to bed. Before I had even gotten out of the garage door, I could tell that something was wrong. There was no orange glow of the heat lamp through the greenhouse plastic roof. I guess the bulb burned out. I don't know how long the heat had been off, but all of the chicks were still alive, huddled against one edge of the draft guard. They're now safe in a cardboard box in the house, with a grow lamp for warmth. If I had been thinking more clearly, I could have put the grow lamp bulb in the brooder, but they're all settled now. The adrenaline is fading, but I'm still a little bit on edge.