Each Electrical Watt generates 3.4144 BTU per hour
A Source 4 with a 375 watt lamp would generate 1195.05 BTU per hour
A Source 4 with a 575 watt lamp would generate 1963.28 BTU per hour
A Source 4 with a 750 watt lamp would generate 2560.00 BTU per hour
For Sensor calculations you should check the Sensor Dimmer Module BTU dissipation.
This calculation is useful for determining air handling in a building based on light output. Electrical Watt hours are different from Kilowatt hours in that Electrical Watt hours are energy output and Kilowatt hours are energy consumed.
BRITISH THERMAL UNIT (BTU): The quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit.