I have several indoor baby habitats, and I have 100 watt Zoo Med Mercury Vapor Bulbs in some and the tube type fluorescent UVB bulbs with reflector in others. I prefer the MVB because then I only have to have two fixtures - one for the MVB for day time and one for the night time heat. With the tube I need three - one with a 100 watt incandescent bulb for heat, the tube plus the night time fixture. With all those fixtures hanging over the enclosure it's hard to change water, etc without taking down a fixture.