Q: What is actually a zero watt bulb?

Answer: A zero-watt bulb is a lightbulb that uses little power. Contrary to the name, these bulbs are not in fact zero watts. The reason they are colloquially called "zero watt" bulbs is because when they were first made, they only had a power consumption rate of 15W but testing equipment at the time was unable to detect such low wattage causing people to think they didn't use any power. Todays "zero watt" bulbs re as little as 10W.