Hi all
Incandescent is not my area of expertise, but I had a (probably dumb) question concerning them.
Is there any type of filament bulb that is polarity dependent? It would stand to reason that polarity really doesn’t matter seeing as its basically a resistor (and not a diode like LEDs) but I got to wondering (dangerous!) if any incans work better with the polarity one way or the other.
They are simply a resistor. Now if anyone includes electronics in the head to control brightness, for example, then it would matter.
Matt
This post got me thinking and I remembered this:
It’s been forever since I read about it so the details and references are absent, but many old British vehicles and some and old Chrysler/Plymouth models used a positive ground system because it causes less electrical connection corrosion. With DC current, electrons flow from negative to positive (true even if it sounds backwards). As best I remember, having the electrons flow from the vehicle battery (smaller metal mass, - polarity) through the electrical load to the car chassis (largest metal mass, + polarity) was the basic reason for this. I do remember that this effect was rather small but it was measurable and scientifically proven.
With the usual tubular Incan flashlight, the largest metal mass is the outer battery casing and the metal strip going forward to the slide-switch (along with the body if it’s metal), which being negative polarity is backwards to this principle. With the usual Incan flashlight bulb the largest metal mass is the outer shell which should also be seeing positive polarity but it’s not.
So this may partially explain why these old lights were so prone to switch and terminal corrosion. Shake, shake, tap, tap- OK we got light again :bigsmile:
Just thought I’d mention this because while an incan bulb filament isn’t polarity-specific, the bulb housing and the flashlight itself possibly could be!
Phil
incans heats up a resistor to make lights.
but in my experience with h4 car bulbs, the positive usually heats up first.
Not too sure why.
I wonder though if changing the polarity every month or year would reduce filament stress in each ends and extend its life.
Thanks for the answers.
I could be wrong, but don’t a lot of HID ballasts output an AC voltage anyway?
HID doesn’t use a filament to produce light, and it isn’t incandescent either, so not relevant to this discussion. Home incandescent bulbs use 120v AC power though. I don’t know if it has any effect on longevity. Perhaps someone would like to connect ten 12-volt batteries together to make 120v DC, and test the longevity of an incandescent versus a similar bulb (same brand, model, and wattage) running on AC.
Whoops…I always assumed HIDs had a filament….you know what they say about assuming.
