UVB is filtered by glass and plastic (except some specially fabricated to pass UV).
If you want to cover the top to keep temperatures steady - this can work. You can use tin foil for that too (it's easier to cut around the light fixtures). But don't cover the enclosure until you have a thermostat to turn the heater on and off
If you want to cover the top to keep temperatures steady - this can work. You can use tin foil for that too (it's easier to cut around the light fixtures). But don't cover the enclosure until you have a thermostat to turn the heater on and off