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Get (incandescent) bulbs rated 130v. A 130v bulb with 123 volts applied will last almost 3 times the rated life. By contrast a 120v bulb with 123v applied will last .7 times the rated life. If you're really curious I can dig out the formula for you. It's in one of my text books.

i want to know your formula dude. email me last_resort9948@yahoo.com. or why not post it here so others can see it also.

thanks!!

cheersss!!!

marcus

If you use 130 volt lamps your light output is dereased. Just something to keep in mind.

This PDF is written for low voltage DC halogen lamps: http://www.walamp.com/lpd/files/applicationnotes/isl297a.pdf

It isn't going to apply exactly to ordinary 120V lamps, but the general trends will apply, since the physics is pretty well similar.

The higher the applied voltage, the more current will flow. The greater the current flow, the more heat generated. The more heat generated, the hotter the filament will get. The hotter the filament, the greater the filament resistance. Net result: unlike an idea resistor where current is proportional to resistance, the current in a filament lamp goes up more slowly than the applied voltage.

The higher the temperature of the filament, the greater the light output and the greater fraction of the light output in the human visual range. At higher voltages the lamp will be more efficient.

The higher the temperature of the filament, the faster the evaporation of the tungsten. The lamp will have a much shorter life.

The relations are pretty significant exponentials. If you increase the voltage to a lamp by 10%, expect a decrease in life by something like 25%. The PDF above has approximate equations for the power, light output, and life of lamps.

-Jon

Sign bulbs have a sturdier filament and more filament supports (typical residental lamps support the filament only at the ends) to allow the lamp to withstand vibrations. You will find a similar construction in "rough service" or "garage door opener" lamps.

Also, operating lamps at a lower voltage will also produce a more yellow light due to the lower filament temperature.

BTW, I used to work for a company that makes programmable message boards and scoreboards, so I'm quite familiar with incandescent lamps, especially those made for signs. If you have more questions, ask, and I'll see what I can remember.

Brian

This is from memory, I'll dig out the text when I get home and add post then. It's from "Electrical Wiring - Commercial"

(Rated Voltage/Actual Voltage)^13 = (Actual Life/ Rated Life)

e.g. Assuming a bulb rated 130v and 1000 hr and receiving 123 volts ...
(130/123)^13 = (X/1000)
2.054X=1000
X = 2054 hours of actual life


In reverse: 120v 1000hr rated and receiving 123 volts
(120/123)^13 = X/1000
.725X = 1000
X= 725 hrs actual life

I'm home now and the formula is correct.
The text is "Electrical Wiring Commercial" Ray Mullin & Robert Smith (Delmar publishers)
It's in unit 14 if you have the book

[This message has been edited by Steve Miller (edited 02-11-2005).]