An improved bed apparatus (4) includes a bed (12) and a movable heater assembly (16). The bed (72) is movably disposed on a support (8), and the heater assembly (76) is movable to enable alignment between the bed (72) and the heater assembly (76) to promote uniformity of irradiance on a patient situated on the bed (72). In an embodiment, the bed (72) and heater assembly (76) are movable together to maintain alignment between the bed (72) and the heater assembly (76). In another embodiment, the bed (72) and the heater assembly (76) are independent, but one or more indicators (244, 254) are provided to enable manual alignment between the bed (72) and the heater assembly (76).