Recently a light under a foot tall cardboard box, seed tray on top, covered was touted. I found that it works well. While I was at it, I built a wooden box (no top or bottom) just larger than a 72 plant seedling tray with cover. Ran wood strips around the inside creating a lip about 1/2 an inch down. Set the tray into the box, put a 60 watt bulb under the box in a wire cage trouble light. Bottom heat a bit strong in this wattage but pretty good germination. Gareth the ChileKnight