Incandescent globes for use in elevated temperature environments (Ovens)

[cc]

Can anyone tell me what are the constructional differences between an
ordinary off the shelf incandescent globe and those that are 300C rated for
uses in ovens and similar environments? It seems to me that all the
component parts of a standard light globe should be able to withstand
domestic oven temperatures, yet they apparently have a drastically reduced
life if used there. I would like to know why the standard globe fails and
why the special one doesn't.
Thanks Charles

 

[Jeff Waymouth]

If I remember correctly, the key difference is the cement which is used
to hold the base to the outer jacket. Standard cement degrades at
common oven temperatures and the jacket would disconnect from the base.

Oven lamps use a cement which can withstand those temperatures.

Jeff Waymouth

 

[TKM]

That's what I recall too, Jeff. Lamps without basing cement can be used at
any temperature -- or at least until the glass melts.

Terry McGowan

 

[Andrew Gabriel]

If I remember correctly, the key difference is the cement which is used
to hold the base to the outer jacket. Standard cement degrades at
common oven temperatures and the jacket would disconnect from the base.

Oven lamps use a cement which can withstand those temperatures.

Jeff Waymouth

Yes, I did use an ordinary one in an oven, and
a) I guess the solder softened as it slightly soldered itself into the
lampholder, and
b) the glass came away from the base.

 

[cc]

Yes, I did use an ordinary one in an oven, and
a) I guess the solder softened as it slightly soldered itself into the
lampholder, and
b) the glass came away from the base.

The issue that I have is just failure of the filament and I would like to
know why that occurs. There was no sign of the cement softening or the
glass envelope coming loose. The local sales people at a couple of
different outlets also said that the problem was the cement softening, but
their version of the story said that the cement failed and let air into the
globe which caused failure of the filament. That is obviously incorrect as
you will be aware the glass envelope is sealed in an airtight unit before it
it fitted into the base.
Charles

 

[TKM]

The issue that I have is just failure of the filament and I would like to
know why that occurs. There was no sign of the cement softening or the
glass envelope coming loose. The local sales people at a couple of
different outlets also said that the problem was the cement softening, but
their version of the story said that the cement failed and let air into
the globe which caused failure of the filament. That is obviously
incorrect as you will be aware the glass envelope is sealed in an airtight
unit before it it fitted into the base.
Charles

It's a reasonable explanation -- particularly if the cement expanded and
caused a seal crack where the feed wires go through the glass and into the
lamp bulb. If the crack is small, you may not see it without
magnification.

You could test the lamp to check for some kind of air leak. Heat the lamp
up slightly in an oven so some of the air inside will expand and be driven
out. Then, submerge the lamp in water and cool the water with ice so any
air inside the lamp cools. That will reduce the air pressure inside the lamp
and draw in water through the leak. After a while, if there is a leak, you
should be able to see water inside the lamp or condensed moisture.

The trick is to get the lamp warm, but not too warm so that it cracks when
you put it into the water. Give both the heating and the cooling plenty of
time.

Terry McGowan

 

[Don Klipstein]

Can anyone tell me what are the constructional differences between an
ordinary off the shelf incandescent globe and those that are 300C rated for
uses in ovens and similar environments? It seems to me that all the
component parts of a standard light globe should be able to withstand
domestic oven temperatures, yet they apparently have a drastically reduced
life if used there. I would like to know why the standard globe fails and
why the special one doesn't.

Besides others mentioning grade of cement between the bulb and the base,
I would like to add grade of glass and whether the bulb has a gas fill or
a vacuum. There are vacuum ones, mostly when design current is less than
..2 amp or design wattage is near or less than 1 watt or less than roughly
8 watts per centimeter of non-uncoiled filament length, also I have yet to
see vacuum with coiled-coil filament.

Vacuum-containing tungsten incandescent lamps appear to me to not have
long lifetime if bulb temperature gets much pastv 150 degrees C.

In addition, gas-filled non-halogen ones intended for high temperatures
(oven duty) are likely to have room-temperature-pressure of the gas fill
somewhat less than in "general service" ones. However, my experience is
that these are gas-filled.

 

[Victor Roberts]

The issue that I have is just failure of the filament and I would like to
know why that occurs. There was no sign of the cement softening or the
glass envelope coming loose. The local sales people at a couple of
different outlets also said that the problem was the cement softening, but
their version of the story said that the cement failed and let air into the
globe which caused failure of the filament. That is obviously incorrect as
you will be aware the glass envelope is sealed in an airtight unit before it
it fitted into the base.
Charles

Charles - all incandescent lamps have some gas contamination
trapped in the glass. One accelerated test run on
incandescent lamps is to operate them, in a small enclosed
can, known as a slumper can, that raises the glass
temperature and accelerates gas evolution.

I do not know how oven lamps are made, but I suspect that
they: 1)either use a different glass, such as borosilicate,
instead of soda lime, that is less susceptible to gas
evolution at high temperature; or 2) the lamp is baked at
higher temperatures during processing; or 3) the lamp
contains a getter to gobble up that evolving gas.

--
Vic Roberts
http://www.RobertsResearchInc.com
http://www.cflfacts.com
sci.engr.lighting Rogues Gallery http://www.langmuir.org
To reply via e-mail:
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It may not be used in any publication or posted on any Web
site without written permission.

 

[Victor Roberts]

Charles - all incandescent lamps have some gas contamination
trapped in the glass. One accelerated test run on
incandescent lamps is to operate them, in a small enclosed
can, known as a slumper can, that raises the glass
temperature and accelerates gas evolution.

I do not know how oven lamps are made, but I suspect that
they: 1)either use a different glass, such as borosilicate,
instead of soda lime, that is less susceptible to gas
evolution at high temperature; or 2) the lamp is baked at
higher temperatures during processing; or 3) the lamp
contains a getter to gobble up that evolving gas.

Charles,

One more question. Are you using a clear lamp or a coated
lamp? The diffusive coatings trap moisture during
processing and then release it when they are operated at
high temperature. You should use only clear lamp in an
oven.

--
Vic Roberts
http://www.RobertsResearchInc.com
http://www.cflfacts.com
sci.engr.lighting Rogues Gallery http://www.langmuir.org
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.