I just set up my first vivarium and got an Exo-terra dual top light fixture, I have 2 T8 Life-Glo full spectrum 15w 6700k, light fixture also has 2 outlets for halogens, but I replaced them with 2 LED 4w-35w bright white light at 3000k.
Vivarium is for orchids mostly, light fixture sits about 20" off bottom of tank strata.