[rescue] Fluorescent Myth Debunking

Wes Will wwill at siu.edu
Thu Sep 16 15:06:50 CDT 2004

>a caveat though: unless they've changed, they don't like being
>power-cycled.  start cycles kill them.  they're best for lights you
>turn on and leave on.

( http://p2.utep.edu/watts/resources/myths.cfm )

Fluorescent Bulb MYTH #1

The energy used to start a fluorescent bulb is so great that it will offset
any energy savings from turning the lamp off.

The energy usage during start up is comparable to 5 seconds or less at
normal operation. Therefore, turning the lights off for more than 5 seconds
will save more energy than leaving them on. (1)

Fluorescent Bulb MYTH #2

Frequent switching of fluorescent bulbs will reduce lamp life, thereby
increasing annual lamp replacement cost.

It is true that the life of a fluorescent bulb - measured in hours - will
be reduced if the lamp is switched more frequently. BUT, by turning the
lamps off, the lamp calendar life - measured in years is usally extended. (1)

Where do these myths come from? Their origin can be traced to the 1940s and
1950s when energy was cheap and environmental costs weren't considered.
Break Even Points

The following guidelines are the times a light needs to be off before the
cost of turning it on again, and the increase in lamp failure are outweighed.

Incandescent Bulbs: 3 seconds

Flourescent Lights: 5 minutes (2)

Mercury Vapor: 30 minutes

Metal Halide: 30 minutes

Halogen: 5 minutes


1) source: United States Environmental Protection Agency, Green Lights Program

2) Lighting Handbook - Reference and Application. 8th Edition. Chapter 30. 
Wes Will
Grant me the company of those who seek truth, and
protect me from those who have found it.

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