1 watt/hour = 3.413 Btu
432 watts (T5) x 3.413 Btu = 1,474.416 Btu
400 watts (HID) x 3.413 Btu = 1,365.2 Btu
You will recall that the cooling power of an air-conditioner is rated in Btu (British Thermal Units) Also, notice that space heaters are rated in watts.