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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. |
"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 |
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