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Re: Long life lights

John Lark>

>> >> >> >>>I've got a problem. I happen to carry the distinction of being the one >>>responsible for changing lights. Much as that's a problem in itself, the >>>biggest problem is.....the front porch light (surprisingly, it's not a >>>stairway light, eh?), which happens to be a hanging, upside-down, enclosed >>>fixture. And they put two screws in the thing, so it's almost impossible >>>for a single person to replace the bulb thus inserted. Really quite >>>remarkable how no one thought of this. >>> >>>Besides modifying it, which I may consider because it's just that bad, in >>>the mean time I need something that'll last. We've already tried the "ten >>>gajillion hour" CFLs, which died in all of, you know it, three months. I'm >>>guessing something high voltage (130V+?) and incandescent. Any >>>recommendations? >>> >>>Tim >> >> A 230 volt incandescent, or a 120 volt one with a diode in series. >> >> I find that, in general, CFs last a long time if run continuously, but >> die when cycled. So a 5 or 7-watt CF might be left on 24/7 and last >> longer and use less net power than an incendescent run at lower >> voltage. >> >> There are some screw-in LEDs available now. I asume they're reliable. >> >> John >> > I do not think the diode will help much as the filament will be >thermally cycling over a much wider range, and the EM self-stress may >also shorten expected life.

My experience is that diodes do help a lot.

Keep in mind that the filaments in blinking marquee lights have a much greater temperature swing than the filament of a lamp in series with a diode.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein
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Evaporation kills filaments, not mechanical stress.

Diodes do greatly extend the life of an incandescent.

John

Reply to
John Larkin

Wouldn't you use a pair in antiparallel?

Thanks, Rich

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Reply to
Rich the Philosophizer

No, that would only drop 0.7 volts or so. A single diode reduces the RMS voltage to about 85.

Lamp brightness goes as about V^3.4, and life goes as V^-16.

John

Reply to
John Larkin

For really long life (and low efficiency), maybe two 120VAC bulbs in series with a diode. Yeah, 2 bulbs 1 diode.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

For 42 volts RMS across each lamp?

How extreme do you want to go? Put two 300W 120V lamps and a diode in series, and power consumption will be about 170 watts. And light output will be about 120 lumens. The light output exponent is more than 3.4-3.5 when voltage is that low.

A 230V lamp or two 120V ones in series should last long enough. I have heard -13 and -14 for that life expectancy exponent, and at times worked out -12 for myself. Even if it is -12, a 750 hour 230V lamp would have median life of 210 years at 120V.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

For 42 volts RMS across each lamp?

How extreme do you want to go? Put two 300W 120V lamps and a diode in series, and power consumption will be about 170 watts. And light output of both combined will be about 200 lumens - about that of a "standard" 25W

120V lamp. The light output exponent is more than 3.4-3.5 when voltage is that low - figure more like 4 for that hot-running lamp, 4.1 on average for others.

A 230V lamp or two 120V ones in series should last long enough. I have heard -13 and -14 for that life expectancy exponent, and at times worked out -12 for myself. Even if it is -12, a 750 hour 230V lamp would have median life of 210 years at 120V.

If you want really extreme, you don't need diodes - just put a few lamps in series. 3 should be overkill, with mean life expectancy (in the unlikely event filament evaporation is still the limiting factor) in the 10's of millennia or more.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

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