my recollection of the equation for life as a function of voltage is that
it's the 13th power, not 6th. - unfortunately, I can't find the GE lighting
handbook I got this out of to confirm.

by the way, if anyone wants some optoelectronics catalogs from the early
70s, contact me off the list
snip
Imagine my surprise when these damned things are only rated for 15
hours!!!!



Well, the life of a bulb is roughly (rated voltage/operating voltage)^6
so (12/5)^6= 191 * 15 hours = 2865 hours. I'd call these 5V bulbs
myself....

I replaced a grain-of-wheat lightbulb for a clock-radio dial with one from
Radio Shack. The supply voltage is 5 volts, so I bought a 12 volt bulb.

Imagine my surprise when these damned things are only rated for 15
hours!!!!

Well, the life of a bulb is roughly (rated voltage/operating voltage)^6
so (12/5)^6= 191 * 15 hours = 2865 hours. I'd call these 5V bulbs...

I was going to post something on this, but refrained. However...

Many years ago, when transistor amplifiers were still new and exotic, Allied
introduced the KG-870, an integrated amp using germanium alloy transistors (you
know, the ones that barely got past 5kHz).

At that time, a lot of attention was paid to protecting the output devices.
(Germanium transistors were prone to thermal runaway.) Allied had an interesting
solution -- the emitter resistors were actually 12V automotive lamps! If "too
much" current passed through the transistor, the bulb's resistance would
increase, restraining the flow.

The bulb was also supposed to be a fuse. The writer of the Electronics World
article explained that the life of a tungsten lamp varied as the 12th power of
the applied voltage. Get the voltage high enough, and the lifetime becomes a
fraction of a second.

He didn't say where he got the 12th-power rule. Anybody know?

In article , Robert Casey wrote:
That's right.

Awesome! I like the sound of that!! :-)

Thanks.

I assumed that if since it was rated for 15 hours that it would last for
30 hours if run at approx half the rated volts.

--
Sven Weil
New York City, U.S.A.

I found graphs in a 1978 GE miniature lamp data book, giving life,
candlepower, and current as a function of lamp voltage. It has a bunch
of qualifications:

"Calculations of characteristics shown in Chart I are approximate only
between 95% and 110% of rated voltage for lamp types with 5,000 hours
life or less. Certain lamp types will vary widely from calculated
values. This chart will not apply to lamps with lives in excess of 5,000
hours. This chart does not apply to halogen cycle lamps."

It extends from 60% to 140% of rated voltage. The text accompanying the
graph says that, "as approximations", the light output varies as the 3.6
power of the voltage and the life varies inversely as the 12th power of
the voltage. It also says of the graphs that "Indicated values (except
for long life lamps) are reasonably valid, between 95% and 110% rated
volts. Beyond that, indicated characteristics may not be realized
because of the increasing influence of factors which cannot be
incorporated into the chart." I assume that long life bulbs are excluded
because they're already running a a considerably lower than "normal"
voltage.

At 60% of rated voltage, the graphs show that the current had decreased
to about 75% of rated current, while the candlepower has dropped to
something like 17% of rated output. (This means the efficiency is around
38% of normal.) Life is around 650 times the rated life.

In the other direction, at 140% of rated voltage, you get about 120% of
rated current, about 325% normal brightness, and about 0.016 times
normal life.

"Double life" bulbs are popular. You can make any bulb into a "double
life" bulb (according to the graphs) by running it at 95% of normal
voltage. Current will drop 3 or 4 percent, and you'll get about 85% of
normal light output.

I'm sure more information is available on the web for anyone who's
interested.

Roy Lewallen, W7EL

030827 1317 - Al wrote:

There's never enough time to do it right the first time.......


Or: There's never enough time to do it right, but there's always enough
time to do it over...

Thanks for the confirmation of 12th power.

It extends from 60% to 140% of rated voltage. The text accompanying the
graph says that, "as approximations", the light output varies as the 3.6
power of the voltage and the life varies inversely as the 12th power of
the voltage. It also says of the graphs that "Indicated values (except
for long life lamps) are reasonably valid, between 95% and 110% rated
volts. Beyond that, indicated characteristics may not be realized
because of the increasing influence of factors which cannot be
incorporated into the chart." I assume that long life bulbs are excluded
because they're already running a a considerably lower than "normal"
voltage.

At 60% of rated voltage, the graphs show that the current had decreased
to about 75% of rated current, while the candlepower has dropped to
something like 17% of rated output. (This means the efficiency is around
38% of normal.) Life is around 650 times the rated life.

In article ,
mentioned...
I replaced a grain-of-wheat lightbulb for a clock-radio dial with one from
Radio Shack. The supply voltage is 5 volts, so I bought a 12 volt bulb.

Imagine my surprise when these damned things are only rated for 15
hours!!!!

Well, the life of a bulb is roughly (rated voltage/operating voltage)^6
so (12/5)^6= 191 * 15 hours = 2865 hours. I'd call these 5V bulbs...

I was going to post something on this, but refrained. However...

[snip]

He didn't say where he got the 12th-power rule. Anybody know?

Well, the GE mini lamp catalog mentions this, and GE has been around
since day 1, so I would guess that they came up with the figure.


--
@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@ h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/e...s/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 at hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@ u@e@n@t@@

"Roy Lewallen" wrote in message
...
I found graphs in a 1978 GE miniature lamp data book, giving life,
candlepower, and current as a function of lamp voltage. It has a bunch
of qualifications:

"Calculations of characteristics shown in Chart I are approximate only
between 95% and 110% of rated voltage for lamp types with 5,000 hours
life or less. Certain lamp types will vary widely from calculated
values. This chart will not apply to lamps with lives in excess of 5,000
hours. This chart does not apply to halogen cycle lamps."

It extends from 60% to 140% of rated voltage. The text accompanying the
graph says that, "as approximations", the light output varies as the 3.6
power of the voltage and the life varies inversely as the 12th power of
the voltage. It also says of the graphs that "Indicated values (except
for long life lamps) are reasonably valid, between 95% and 110% rated
volts. Beyond that, indicated characteristics may not be realized
because of the increasing influence of factors which cannot be
incorporated into the chart." I assume that long life bulbs are excluded
because they're already running a a considerably lower than "normal"
voltage.

At 60% of rated voltage, the graphs show that the current had decreased
to about 75% of rated current, while the candlepower has dropped to
something like 17% of rated output. (This means the efficiency is around
38% of normal.) Life is around 650 times the rated life.

In the other direction, at 140% of rated voltage, you get about 120% of
rated current, about 325% normal brightness, and about 0.016 times
normal life.

"Double life" bulbs are popular. You can make any bulb into a "double
life" bulb (according to the graphs) by running it at 95% of normal
voltage. Current will drop 3 or 4 percent, and you'll get about 85% of
normal light output.

I'm sure more information is available on the web for anyone who's
interested.

Roy Lewallen, W7EL


Running a lamp undervoltage sure does work. I put 220 volt bulbs in a 110v
porch light. Bright
enough to see ok and they have lasted for 8 years now being on nearly every
night!
I don't care if I get as lumens per watt as the house next door. It works!
Ghost

"William Sommerwerck" wrote in message
...
I replaced a grain-of-wheat lightbulb for a clock-radio dial with one
from
Radio Shack. The supply voltage is 5 volts, so I bought a 12 volt bulb.

Imagine my surprise when these damned things are only rated for 15
hours!!!!

Well, the life of a bulb is roughly (rated voltage/operating voltage)^6
so (12/5)^6= 191 * 15 hours = 2865 hours. I'd call these 5V bulbs...

I was going to post something on this, but refrained. However...

Many years ago, when transistor amplifiers were still new and exotic,
Allied
introduced the KG-870, an integrated amp using germanium alloy transistors
(you
know, the ones that barely got past 5kHz).

At that time, a lot of attention was paid to protecting the output
devices.
(Germanium transistors were prone to thermal runaway.) Allied had an
interesting
solution -- the emitter resistors were actually 12V automotive lamps! If
"too
much" current passed through the transistor, the bulb's resistance would
increase, restraining the flow.

The bulb was also supposed to be a fuse. The writer of the Electronics
World
article explained that the life of a tungsten lamp varied as the 12th
power of
the applied voltage. Get the voltage high enough, and the lifetime becomes
a
fraction of a second.

He didn't say where he got the 12th-power rule. Anybody know?


Lamps and PTC thermisters are used as non-linear resistors. The diode knee
is also very non-linear. Lamps are sometimes used in the feedback loop or
good clean sine wave oscillators. They stabilize around the non-linearity.
Ghost

Bob wrote:
Looking for tiny incandescent lamps for my TM-451A Kenwood.

Apparently these are 6 V or so; there are four of them in
series parallel controlled by a regulator to vary intensity.
They light up the LCD and two of them are burned out.

I have searched many of the usual sources and can't seem to
locate replacement lamps; as a last resort I could go to
Pacific Parts but they are so expensive. These are just
inexpensively made tiny bulbs with wire leads.

Any suggestions?

Bob

Perhaps one of these might fit the bill, LED replacements for typical
incandesents...

http://dkc3.digikey.com/PDF/T033/1200.pdf