I'd put a 22'' T5 over the elevated portion and set a PAR38 halogen flood light (start with maybe 70w and see how that does for temps) and go from there. If you can set the flood light to a dimming thermostat or dimmer you can fine tune the output to compensate for temperature changes around the tank once the temps are pretty close using wattage. I'd keep the area under the shelf relatively dark to act as a hide/shade area. Maybe a CHE on the other side that you can turn on if winter nights get cold but if room temp stays above about 70 it isn't needed.