[Vwdiesel] Glowplugs --- ( Afterglow -- afterthought's ).

[Roger Brown]

Val Christian wrote:
>
> A recent table check on lamps, shows that lowering from 12V to 11.5V doubles
> the life of the bulb.  -Val

True for a normal tungsten filament light bulb, but in the case of a quartz-halogen bulb, lowered voltage can lead to lessened
life.  Any light bulb filament will boil off metal ions as it heats up, the hotter it gets the more boil off there is.  However,
in a halogen-filled lamp, the hot gas forces the metal ions back to the filament's surface, through a process highly dependent
on the temperature.  Run at a slightly reduced voltage (and thus filament temperature) and the process doesn't work well and the
light burns out faster.  This is why you want to run a high current relay wiring harness with halogen headlights, as even 1/2
volt drop at the bulbs can cause them to burn out faster.

Most of the "long life" bulbs you see are simply built for higher than nominal voltages, for 120V, a 130V or 140V bulb is used
for longer life.  Its often less efficient in terms of lumens/watt than a bulb running at its rated voltage.

--
    Roger