When to Turn Off Fluorescent Lights

April 7, 2008

Compact Fluorescent BulbAs more and more homes have compact fluorescent lights, questions are arising about when (or even whether) they should be turned off. One school of thought is that it takes a huge surge of electricity to start fluorescent lights (like those institutional tubes in your 6th grade classroom), and turning the lights on and off actually uses much more electricity than just turning them off when you are out of a room for a while.

In a word: WRONG!

As a good rule of thumb, if you don’t need the light for five minutes or more, turn it off.

The energy needed to start a fluorescent light, whether a compact fluorescent or a traditional, linear tube, is slightly higher than what it needs for continuous operation once it has started, but only slightly so. According to the US Department of Energy, it is the equivalent of just a few seconds of operation. So in almost any instance, from an energy savings perspective, it makes sense to turn it off.

The other consideration is the life of the bulb itself. There is some stress placed on a fluorescent light every time it starts up. A fluorescent light that is repeatedly turned off and on will, on average, have a shorter life than one that is constantly lit. But while this is a consideration, it isn’t the most important one.

Rubinstein notes that, even for fluorescents, the cost of electricity over a bulb’s lifetime far outpaces the cost of the bulb itself. “Even if you switch a fluorescent light on and off frequently,” he says, “the slight reduction in lamp life is a small effect relative to the energy savings you accomplish by being a good citizen.” Gotti adds that the reduction in lamp life from frequent on-and-off switching can often be counterbalanced by the extension of “calendar life”—the actual passage of time between lightbulb replacements—that results from using the bulb for fewer hours.

One of the biggest complaints with some compact fluorescent bulbs is that they only have a fair color rendering index, and are even poorer when they first start. If color accuracy is an issue, it may make sense in certain cases to leave the lights on a little longer, but generally, compact fluorescent lights reach their full output after just a brief time.

Replacing inefficient incandescents with compact fluorescents can help, but the small measure they represent shouldn’t be mistaken for solving the whole problem. While compact fluorescents are the poster child for energy savings, other home equipment like heating and cooling equipment and water heaters have more impact on the overall energy usage of a home.

via: Scientific American