On Sun, 2008-08-03 at 19:40 -1000, Ken Brown wrote:
> >
> >> LEDs may disappoint you very much.
> >>
> >
> > Yes. I own five 229/238 tuners. I put LED's in the first one I
> > bought. Didn't even consider doing it to the others. Instead, buy 14
> > volt, long life incandescent bulbs from a good industrial
> > electronics supplier.
> >
> >
> Unless the stock bulbs are 6.3 volt lamps, in which case you will want a
> lower voltage, perhaps 7 volt rating, to make it last a lot longer than
> a 6.3 volt lamp.
>
> DE N6KB
>
A GE tungsten lamp book that I have gives these rules of thumb. Lowering
the supply voltage by 5% reduces the light output by 10% while doubling
the lamp life. Conversely, raising the voltage by 5% increases light
output 10% while cutting lamp life in half. Extending this (which goes
logarithmically) to running a lamp at half voltage, the expected life
can be as long as a century as evidenced by a carbon filament lamp in a
San Francisco fire house running (dull red glow) at half voltage for a
century so far. I've applied 240 volt 100 watt lamps with 120 volts
applied to supply a little heat in outdoor solenoid boxes (on a corn
dryer), and lamp life has not reached a century, more like a decade
running constantly.
It was standard practice in Collins high power transmitters to include a
resistor in series with each lamp to extend life. I think the resistor
was chosen to drop the voltage about 10%. I made it practice also to
choose lamps with longer lifetimes at their rated voltage.
In some sizes of panel lamps, different numbers have different lifetime
and light emission ratings. Short lived lamps may be only expected to
last 750 hours, while some may be rated for 5000 hours or more. When
comparing this data it will be clear that the long lived lamps produce
less light per watt of electric power, sometimes distinctly. The data is
only believable from domestic lamp makers, not from offshore copies of
these lamps.
73, Jerry, K0CQ
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