How do they react with the lamp? Do they huddle under it, or mostly stay away from it? My biggest concern, since you are planning to be away, is actually fire danger (depending upon who is going to be taking care of them during that time). I would try, today, turning it off and watching their body language. If they don't even notice it, you won't need it. How many chicks? Do they have a "huddle" area to keep each other warm at night? It would be great if you just had one less thing to worry about on your trip.