Not sure what kind of heat lamp you’re using, but in general the red bulbs are less imposing than the bright white bulbs. You can get them at pet stores, just gotta make sure the fixture can support the strength of bulb you’re getting (They will say up to 120Watts or 74Watts etc). I used to keep outside rabbits when I was in high school and we kept the bulb right over the water bottle to keep it from freezing. Also, stuffing extra straw in the nest box can keep them nice and toasty