Quoting Apptech <apptech@paradise.net.nz>:

> Any thoughts on the longevity of tungsten bulbs running on
>
> - AC supply
> - Same supply but full wave rectified.
> - Same supply but full wave rectified and filtered to DC.
>
> The bulb is in fact two 12V bulbs in series running from a
> nominal 16 VAC supply.
>
> In the second case the filament has a constant polarity bias
> but is exposed to cycles of heating and cooling which
> intuitively (to me) feel the same as for AC.
>
> In the third case the DC voltage will tend to be higher than
> the RMS AC voltage so the bulb will operate at a somewhat
> higher wattage.
>
>
>
>         Russell


Life should be better with the same RMS voltage AC, particularly if the
filament is relatively thin. DC is known to cause "notching" (there's your
search term) on tungsten filaments, and there are modified tungsten
filaments that have better life on DC. Eg:

http://www.harison.co.jp/english/p_pro1_info.html

So, I predict average life will be longest for a), shortest for c) with b)
in the middle.

Best regards,
Spehro Pefhany
-- 
"it's the network..."                          "The Journey is the reward"
s...@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com


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