# lumens vs voltage; incandescent

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How does voltage effect lumens in a incandescent bulb?

A bulb rated 420 lumens at 130VAC will output how many lumens at 115VAC?

• posted

Also, Fig 4:

and Fig 2:

```--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com ```
• posted

Thanks Jeff. Looks like 130VAC bulb operating at 115 looses about 30%.

• posted

Light output is reckoned to vary with the power 3.5 against rated voltage. Lifetime inversely to the 12th power. So intensity will be a bit lower, lamp lifetime will be much greater.

So 115 vs 130VAC is 65% light reduction or 273lumens to answer your question. (Lifetime at 115v will be more than four times 130V life.)

piglet

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Correction. Please forgive sloppy language: meant reduced *to* 65% of rated output not reduced *by* 65%. IOW 420 * 0.65 = 273

piglet

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30% lower light and three times the life is the usual rule for 10% lower voltage.

Cheers

Phil Hobbs

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130 volt Halogen and incandescent light bulbs are manufactured with a thick filament designed to withstand a theoretical 130 volts. I say ?theoretical? because almost all homes in the US operate on only 110-120 volts. The thicker filament in a 130 volt bulb, when operated on typical

110-120 line voltage, has a higher resistance to the electrical current flowing through the filament, decreasing the amount current across the filament. As a result, the bulb burns cooler, uses less energy (watts), and lasts longer; however, as a trade-off, the bulb is also slightly dimmer and has a lower (more yellow) color temperature.

Thicker filament in a 130V bulb? Riiight.

Cheers

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Syd```
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Not thick wire, right. Tungsten bulbs working ar mains voltage use coiled-coil filaments, so a fatter coil of the same wire gauge will have a higher resistance.

Cheers

Phil Hobbs

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Low voltage bulbs, like 12 volts, seem to last a long time. Maybe a thick filament has more metal to boil off.

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John Larkin         Highland Technology, Inc
picosecond timing   laser drivers and controllers ```
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It's also mechanically stronger.

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Yes, plus the filament is more nearly isothermal. 220V bulbs are quite a bit more fragile than 120V ones.

Cheers

Phil Hobbs

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bit more fragile than 120V ones.

back when all stage lighting was incandescent I saw a lot of companies usin g PAR64 lamps with 120V bulbs in series pairs on 240V

-Lasse

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That fit function doesn't apply across the whole range though, especially towards higher voltage. Once the tungsten melts, it's all over.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
Principal Consultant ```
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C?

r.

Tungsten halogen lamps are complicated beasts. The halogen gas inside the s ilica envelope reacts with evaporated tungsten vapour to produce a volatile tungsten halide, which doesn't condense on the inside of the silica envelo pe (if the lamp is being run hard enough to keep the envelope warm), and ev entually circulates past the hot filament, which is hot enough to decompose the tungsten halide, which decomposes into tungsten - which condenses onto the filament - and halogen gas, which is recycled.

The cute bit is that the hottest bits of the filament decompose more halide , so that the wire thickness remains sensibly uniform along the filament - no hot spots.

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Bill Sloman, Sydney```
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It's actually the high gas pressure (requiring the strong quartz envelope) that retards hot spot formation, by slowing down diffusion of vapour/halide away from its point of origin.

The hot spots aren't enough hotter for there to be a significant difference in the sticking probability of an incident molecule. This is especially true in the early stages of hot spot formation, which you want to slow down as much as possible.

Also the redeposited tungsten tends to form largish crystals, so the redeposited metal is nonuniform.

The halide mechanism is thus sort-of regenerative, but its main purpose is to keep the very small envelope clean. Normal low pressure bulbs reduce darkening by spreading the condensed tungsten over an area ~100x larger, but a bulb that big with the kind of internal pressure required to reduce diffusion would be very dangerous, and the internal convection loss would be gigantic.

Cheers

Phil Hobbs

```--
Dr Philip C D Hobbs
Principal Consultant ```
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Question.... does operating a halogen bulb on a lower voltage with a dimmer for example, offer the same lifetime advantages vs efficency tradeoffs as does a conventional incandescent?

or are the low voltage tradeoffs significantly different?

Mark

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Tends to ruin them with tungsten plating out on the quartz envelope preventing light escaping and not being recycled properly as the volatile halogen compound back to the filament where it decomposes into metal and releases the halogen again. Run too cold the stuff plates out on the cooler envelope and never makes it back to the filament again.

Lifetime and light output both potentially compromised.

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Regards,
Martin Brown```
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The primary evaporation rate will still basically set the life of the bulb, so I'd expect the life to improve at about the same rate as with normal argon-filled bulbs, for sufficiently small voltage reductions. (How's that for physics weaselling?) ;)

At some point the halogen mechanism shuts down and bulb darkening sets in, though. IME that's generally reversible if you crank it up to full brightness for awhile.

Cheers

Phil Hobbs

```--
Dr Philip C D Hobbs
Principal Consultant ```
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You've got to decompose your tungsten halide molecule before you've got an an incident tungsten atom to stick onto anything.

The decomposition is going to happen close to the filament, and it's going to happen faster where the filament is hottest - convection currents are go ing to be faster there too, delivering more tungsten halide into the hot zo ne.

Got any pictures? "Largeish" in the context of a coiled-coil tungsten filam ent would probably only show up in an electron-microscope photograph.

True.

The halide regeneration was developed to beat that particular limit - with the halogen in the gas mix you can get away with running the filament hotte r, and in a more compact envelope. If memory serves, the scheme was origina lly developed to make better bulbs for car head-lights and it was a while l ater before you could get tungsten halogen bulbs for domestic lighting - an d the first generation of them showed their automotive origins by needing s tep-down transformers to let them run at 12V.

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Bill Sloman, Sydney```
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A little bit more, but not nearly _enough_ more, especially in the early stages, as I say. Iodide vapour decomposes everywhere, and so redeposits everywhere. To retard hot spot growth, you need a lot of extra vapour right there, and the only way to get that is by slowing down diffusion.

Largish in the sense of "comparable to the wire radius".

Someplace on the web, there was a great picture of a well-used BMW headlamp filament, but I couldn't find it again in a quick search. It had tungsten crystals comparable in size to the filament radius, which was _big_. You can probably find it in a few minutes if you look.

I remember "high intensity" desk lamps back in the '60s that used halogen bulbs. I think slide projectors had them very early too. Most bulbs used in projectors are low voltage to this day, because the coarser gauge filaments last a lot longer at the same temperature--lots more metal available per unit area.

Cheers

Phil Hobbs

```--
Dr Philip C D Hobbs
Principal Consultant ```

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