I do add heat at night when it's down to the mid 20s or below. And last winter I used a heat lamp. But unless you use safety to the nth degree (guard, appropriate housing for the bulb, securely connected (NOT with the clamp) to two diff. points, etc.), you're going to worry about using a heat lamp. I remember doing the same thing last winter, waking up and going to the window just to "check." So you can NOT use it (and they WILL be okay at those temps if it's draft free) or find another temporary heat source that is safer. Have you looked into the cookie tin or clay pot heaters frequently used for waterers?? Even something like that would add a little warmth...