DIYbanter - View Single Post - Compact Florescents burn out at the same time

In article ,
wrote:
On Mon, 1 Aug 2005 19:54:23 +0000 (UTC), (Don
Klipstein) wrote:

I have seen lightbulbs do this, although not yet seen a trouble light do
this (I am not around trouble lights in use enough to see this).

If the filament has any sharp turns, part of the filament can get
shorted by mechanical shock. This results in the remainder of the
filament getting full line voltage.
I have seen this happen with nightlight bulbs and christmas bulbs with
multiple-support filaments with sharp turns at the supports, and also with
chandelier bulbs with V-shaped filaments.

I give a possibility that other styles of filament could become
partially shorted if stretched out of shape from an impact.

I do consider it possible that if a portion of a filament gets severely
stretched with the remainder of the filament unstretched, then the
stretched portion will run cooler, have reduced resistance, and allow the
filament to get excessive current and possibly total light output could
increase. I have seen filaments unevenly stretched by impacts/shock that
were obviously very uneven in temperature.

So, if the filament shorts or overlaps itself or any of these things,
then when the light gets brighter, I would assume the wattage also
increases, and thus the amount of electricity being used. Is this
correct?

This is correct. Most lightbulbs that I see brightened by mechanical
shock have enough filament shorted to increase power consumption 10-20%.
If the filament is partially shorted but not stretched, it's roughly a
square root thing. Unstretched filament with more than roughly 40%
overcurrent will melt instantly.

This leads to yet another point. If the wattage does
increase, and it was a 100 watt bulb in a fixture rated at maximum
wattage 100w. Then the fixture is really overloaded, right? I
suppose this could actually become a safety issue, even though the
bulbs generally burn out soon.

If the fixture barely does not overheat with an undamaged bulb and
cannot handle the extra heat from bulbs damaged this way, then it is a
safety issue. I would think that trouble lights would be made to take
into account stretched filaments consuming extra power, whether or not
more light resulted. Now I wonder if that's wishful thinking...

- Don Klipstein )