WHEN TO TURN OFF YOUR FLUORESCENT LIGHTS?

A rule of thumb is the more energy saving the bulb is the longer you can leave it on.  Instead of turning them on and off all day long like you would a regular light. 

The cost effectiveness of turning fluorescent lights off to conserve energy is a little complicated.   A general rule of thumb for when to turn off a fluorescent light is if you leave a room for more than 15 minutes, it is probably more cost effective to turn the light off.   So if you leave the room for only up to 15 minutes, it will generally be more cost effective to leave the light or lights on.

Fluorescent lights are more expensive to buy, and their operating life is more affected by the number of times they are switched on and off, relative to incandescent lights.   Therefore, it is a cost trade off between saving energy and money by turning a light off frequently and having to replace the bulbs more frequently.  This is because the reduction in usable lamp life due to frequent on/off switching will probably be greater than the benefit of extending the the useful life of the bulb from reduced use.  By frequent we mean turning the light off and on many times during the day.

The most cost effective length of time that a light or lights can be turned off before the value exceeds the cost of having to replace bulbs (due to their shortened operating life) will depend on the type and model of bulb and ballast.   The cost of replacing a bulb (or ballast) depends on the cost of the bulb and the cost of labor to do it.

Lighting manufacturers should be able to supply information on the duty cycle of their products.  In general, the more energy efficient a bulb/light is, the longer you can keep a light on before it is cost effective to turn it off.

Us Department of Energy