"William Sommerwerck"
"Phil Allison"

** What "issue" is that ??

There are actually two issues.

One... A halogen lamp has to run at or above the temperature at which the
tungsten is redeposited on the filament more rapidly than it evaporates.


** Irrelevant.

The TRUTH is that the re-deposited metal does NOT repair the damage done to
the filament - there are many pics that show this.

The halogen cycle merely keeps the quartz glass clean !!


This temperature is presumably well-above the temperature of a
conventional incandescent lamp. It's reasonable to assume that reducing
the filament voltage some unstated amount will lower the temperature below
the critical recycling temperature, but still high enough to cause the
filament to rapidly burn out. No one here seems to have any information
about this.


** The simple fact is that halogen lamps do NOT have especially long lives -
any more than non halogen lamps with the same filaments.

"Halogen lamps are manufactured with enough halogen to match the rate of
tungsten evaporation at their design voltage. Increasing the applied
voltage increases the rate of evaporation, so at some point there may be
insufficient halogen and the lamp goes black.

** See - it is all about the darn glass.


Over-voltage operation is not generally recommended. With a reduced
voltage the evaporation is lower and there may be too much halogen, which
can lead to abnormal failure.

** Note weasel words.

At much lower voltages, the bulb temperature may be too low to support the
halogen cycle, but by this time the evaporation rate is too low for the
bulb to blacken significantly.

** Still all about the darn glass.


There are many situations where halogen lamps are dimmed successfully.

** Not many - ALL !!

However, lamp life may not be extended as much as predicted.

** The predicted life extension ( power of 12 or 14 ) is not usable beyond
about 10% voltage reduction as the numbers become huge.


The life span on dimming depends on lamp construction

** Yep.

And the one thing that matters most is the GAUGE of the wire in the
filament.

Most halogen lamps are LOW voltage, hence THICK filaments - leading to
longer life than for high voltage ( ie 120V /240V) lamps of the same power.

It is sooooooo simple - if the surface temp is the same but there is way
more material then it takes longer for the filament to wear out.


..... Phil