Q: Is it more energy efficient to keep turning fluorescent lighting on and off all day or to just leave it on? Our office uses the room at least every 20 minutes during an 8-hour work day but no one is ever in there all day.
A: By leaving fluorescent lamps on you save the lamp life, but not energy costs.
It’s a trade off between buying new fluorescent lamps which are generally pretty cheap and the cost of electricity to run the lamps all day for 20 minutes of actual use. This depends on your cost of electricity. Basically, we’ve found it more energy efficient to turn lights off when not in use. (For that type of room it might be cost effective to install an occupancy sensor unless people actually turn the lights off when they leave.)
Q: Is it more energy-efficient to let a light bulb burn for a short period of time, or to turn it off and then on again? I read once that the surge in power when a bulb is turned on is equal to letting the bulb burn for a while?
A: It is more energy efficient to turn the light off than to leave it on. Energy is measured with respect to time. The unit used to measure electrical energy is the kilowatt-hour or thousand-watt-hour, the amount of power or watts that you use in one hour. The momentary or millisecond or less surge of electricity required to start your light bulb will not impact your energy cost, but leaving it on all the time will. With the rising cost of energy, it’s probably a good idea to turn the lights out when you are not using it.
(Not to mention the pollution impact, less energy use, less emissions from power plants.)
Turning the lights on and off a lot will impact your lamp life, however. If you compare the number of bulb(s) you need to buy versus the cost to let the light burn all the time, it will still probably be cheaper to turn the lights off.