General Notices
1. Myth: You save on energy bills by leaving lights on!
Some people believe that the energy to turn on lights exceeds savings of turning lights off.
To test the myth, energy usage was measured during start up, maintenance (steady state), and shutdown.
For steady state energy consumption, several different types of bulbs were turned on for 60 minutes and consumption using a Kill A Watt was measured for the following:
Incandescent 90Wh, Compact Fluorescent (CFL): 10Wh, Halogen: 70 Wh, Metal halide 60Wh, LED: 1Wh and Fluorescent: 10Wh.
For start up energy consumption, an inductive current loop was hooked up to a computer. This measured the amount of energy used when the bulbs were turned on. With an inductive current loop, a wire is run through the centre, which induces a current in the loop. This current is then measured by a digital sampling oscilloscope.
Based on the amount of energy consumed turning on the bulb, calculations were made on how long the bulb would have to be turned off in order to make it worth the energy savings, i.e. ‘It’s best to turn off the bulb if you are leaving the room’:
Incandescent: 0.36 seconds
CFL: 0.015 seconds
Halogen: .51 seconds
LED: 1.28 seconds
Old fluorescent: 23.3 seconds
Modern fluorescent: 0.09 seconds
In other words, it’s almost always best to turn the bulb off. Even the 23 seconds for the fluorescent lights isn’t very long, and the rest of the times are pretty much blinks of an eye.