Posted: Thu Sep 18, 2008 8:49 am
Puting two (or more) bulbs in series does not give the same lifespan as using a series resistanceMrAl wrote:Hi there,
There might be something to be said about resistance vs Triac phase
control vs Diode. ......
whereas the pure resistance method (two bulbs in series) would not. This could make a big difference.
These three techniques are all different and need to be evaluated
The diference is that a hot bulb filament has a bigger resistance that a cold one.
If you put bulbs in series, when you apply the voltage there is allways one of the bulbs that heats up first, increases its resistance and recieves more than its share of voltage and power. As the other bulbs heat up they balance themselves, but as the "quick" bulb gets the (nearly) full voltage each time it will eventually fail.
This was a problem with the old "AC/DC radios" (circa 1920) that had the valve heaters in series, and also with the Cristmas tree light strings (the "classical" ones wired in series).