Question:
I have heard that fluorescent lights should only be used when the temperature is above 45°F. Secondly, I’ve heard that fluorescent lights shouldn't be turned off if they are going to be turned back on within two hours. Could you confirm whether these two ideas are factual or not?
Answer:
Both of your questions refer to myths that are frequently discussed and written about. The response to both of the myths you refer to is "Not Exactly."
Temperature affects the ability of a fluorescent lamp to start and also affects the lamp's light output. Manufacturers have information about the starting temperature of Compact Fluorescent Lamps (CFLs). Most can start at temperatures above 0°F and some are rated for lower start temperature. In cold weather, it may take longer for the light to warm up and reach full brightness.
I personally have had good results using CFLs in my outdoor fixtures in a moderate climate. CFLs typically last for 10,000 to 20,000 hours—about ten times as long as incandescent lamps. Especially when outdoor lights are left on all night, CFLs are a good choice to reduce energy cost.
A common misconception is that a CFL requires a lot of energy to switch on and it is therefore more cost effective to leave the light on than it is to switch it frequently. However, the additional power required for turning on a lamp is only equivalent to about 5 seconds of lamp operation. Therefore, it is always more energy efficient to turn off the light when you leave the room. The issue with turning fluorescent lights on and off frequently—very frequently—is that lamp life can be slightly reduced. The reduction depends on the design of the light and the type of starting system (i.e., magnetic or electronic ballast). With recent technological advances that improve CFL lighting and increase longevity, along with CFL cost decreases, switching is less of an issue.
Here are two good references that address the myths:
When to Turn Off Your Lights
Tips for Using Compact Fluorescent Lamps