But the light output goes down with at least as strong a function, I
believe. So although you can greatly extend the life of a bulb by
reducing the voltage, you also greatly reduce the light output. And
without nearly as much of a reduction of the input power. So you end up
with a dim, very inefficient bulb. That might be ok for some
applications (say, if it's at the top of a tower where it's a really
major pain to change) but not others (like all the bulbs in your house,
unless you love to pay that electric bill).

Roy Lewallen, W7EL

Robert Casey wrote:

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....

But the light output goes down with at least as strong a function, I
believe. So although you can greatly extend the life of a bulb by
reducing the voltage, you also greatly reduce the light output. And
without nearly as much of a reduction of the input power. So you end up
with a dim, very inefficient bulb. That might be ok for some
applications (say, if it's at the top of a tower where it's a really
major pain to change) but not others (like all the bulbs in your house,
unless you love to pay that electric bill).

Roy Lewallen, W7EL

Robert Casey wrote:

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....

In article , Robert Casey wrote:
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....

Rob, I'm probably being dense but I don't follow the math. Then again
I was never really good at math.

what is the ^6? Elevated to the 6th power? So is this bulb going to
last a while?

P.S.: If it blows in my lifetime I'm not replacing it again. The only
reason I did so the first time was because the original had blown its
glass envelope (I _don't_ know why). Yikes!!

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

In article , Robert Casey wrote:
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....

Rob, I'm probably being dense but I don't follow the math. Then again
I was never really good at math.

what is the ^6? Elevated to the 6th power? So is this bulb going to
last a while?

P.S.: If it blows in my lifetime I'm not replacing it again. The only
reason I did so the first time was because the original had blown its
glass envelope (I _don't_ know why). Yikes!!

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

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?

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?

Sven Franklyn Weil wrote:

In article , Lizard Blizzard wrote:



eventually burn out, too. So it would be wise to do the right thing and
replace them with LEDs, and they will last tens of thousands of hours.



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
myself....

In article , Lizard Blizzard wrote:

eventually burn out, too. So it would be wise to do the right thing and
replace them with LEDs, and they will last tens of thousands of hours.

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!!!!

Are there any 5 volt LEDs around?

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