JK> A member of my congregation says that it is cheaper to leave a light on
 JK> all day long than it is to turn it on and off twice, whether florescent
 JK> or incandescent.  Is this true?  Can anyone point me to published
 JK> information?
The lights discussed in this echo wouldn't stay lit that long.  Ignite a 
flash pot, and it's gone.  
That's not true as to electric costs of other lamps, especially incandescant. 
 He's telling you an old wive's tale.  
 
With vapor lamps, energy for several minutes to start up is much higher than 
idling power consumption, but either is higher than off.  Vapor lamps 
generally are only used where they'll be on for hours at a time.  Bulb life 
is designed for long burns per start, and can be shortened, at a cost of 
replacement if that requires a bucket truck or lift.  
Flourescants likewise have a design life that can get shorter with excessive 
starts.  Still, with typical energy costs ten times bulb costs or more, only 
a high labor to replace location can make starts more expensive than 
electric.  8' single pin tubes only work well when warm, and can take several 
minutes to optimize.  
Simply measure or calculate power consumption, multiply by time, and your 
electric rate, over the design life of a lamp.  Compare that to the lamp cost 
and replacement labor, if that has a value.  
160 W (4x40W fl) x 20,000 (hours life) = 3,200 KWH
At $0.12/KWH, that's $384 of electric over the life of one set of bulbs.  If 
you cut the elecctric cost in half turning it off half the time, and shorten 
the bulb life 20% from more starts, that's $192 versus a 20% life decrease on 
4 flourescant tubes, over several years.  
Terry
--- Maximus 2.01wb
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