a blacklite will be fine 24/7.ive looked at home depot and never seen dimmers that are not the ones you wire into a wall.you need a piggy back dimmer.look at lowes.the white light you were using is meant to give off a solid beam of light or basking spot.it will raise the ambiants as well but a blacklite wont focus all the heat to one beam and still raise you air temps.if you cant find a dimmer for the bulb try raising the bulb 6 inches or so above the screen lid.