Consider two identical rooms one with an energy saving LED l

Consider two identical rooms, one with an energy saving LED lightbulb of 30 watts in it and another one with an inefficient incandescent bulb of the same wattage. If all the doors and windows are closed, which room will be hotter after 5 hours and 32 seconds of operation starting from the same temperature of 70 Fahrenheit? Why?

Solution

Answer: The room with inefficient incandescent bulb will be hotter.

Why?

Answer: Incandescent bulbs convert less than 5% of the energy they use into visible light, averaging about 2.2%. This means incandescent bulb produces around 12% heat, 83% IR in the form of heat and only (or less than) 5% visible light.

However, the efficiency of Light Emiting Diode (LED) bulbs is typically in the region of 5-40%, meaning that it is somewhere between 60 and 95% of the input power is lost as heat. That is, a typical LED bulb might produce 15% visible light and 85% heat.