A true watt is the calculation you want to know to assess your growing sun’s real energy consumption. The real electricity used by both the electrical circuits and the lamps themselves â fans, etc. â is referred to as true wattage. While true wattage is a good indicator of power generation, it is not a good measure of light intensity because you have no idea how effective the system is. PPFD is the only real and useful indicator of light output for growing lamps.