Do Halogen Lamps Sing Before Filament Failure?

"D from BC" kirjoitti viestissä: snipped-for-privacy@4ax.com...

I heard just last week one ordinary (non-halogen) 40 W lamp singing for minute or two before failure.

-ek

why limit to halogen lamps?

Cannot say; look at the songbook...

O'Halogen.... O'Halogen...

I dunno - do androids dream of electric sheep? ;-)

Cheers! Rich

D from BC wrote in news: snipped-for-privacy@4ax.com:

Possibly an arc jumping the small gap between the filament ends? I've noticed a couple of such lamp filaments with crystals of what I assume was tungsten that might have grown from vaporized tungsten--no slight feat considering the boiling point of that metal!

I've seen melted quartz tubes on them, too.

--Damon

I just never imagined these lamps to make noise. Could be an annoyance if say halogen lamps were used in a recording booth.

If there's a purpose to human sleep dreaming then androids may dream too until they become terminators. :P

huh... Arc oscillation. I'd go for that.

I've only had them noisy near to failure point, or when improperly dimmed. But that's just my experience!

I'd suspect mechanical resonance. Due to thermal expansion, there's an enormous amount of 120 Hz mechanical forcing on filaments, with only a one-pole rolloff (thermal mass) to control it, so they're carefully designed to avoid resonating at low harmonics of 60 Hz. Triac dimmers put out a lot of highish harmonics, which is why they make the filaments sing, especially at low brightness settings.

Filaments fail due to thin spots developing, and it's quite unlikely that there'll be only one thin spot. Thus the stiffness of the filament will decline during its life, and near failure it could easily be floppy enough to detune the resonance to a low harmonic of 60 Hz.

Cheers

Phil Hobbs

iirc my frequencies, what I heard was high pitch. Above 1Khz.

I think of this phenomenon as "stable burnout arc".

Filament breaks, and an arc forms in the gap.

In most gas-filled incandescent lamps, especially if the filament breaks while cold and the current is higher and the arc is hotter and more conductive, the electric field along the filament is sufficient to expand the arc. The arc's ends crawl along the filament rapidly, until the arc is in parallel with nearly all of the filament, and then the filament does not limit its current. This is how we get the Big Blue Flash.

But in the common 300W and 500W linear halogen lamps, the filament's overall length is greater, the electric field is less, and also the gas is at a higher pressure. When the filament breaks, especially if it does so while hot, the arc does not expand, but stays stable in the gap.

One more thing - a "stable burnout arc" produces little light. Argon does not produce much light when current is in the amp ballpark, especially at pressure in the atmosphere ballpark. The arc is a "high pressure arc", and argon ones typically have something like (I guesstimate) 20 watts per centimeter of arc length in heat conduction loss when they are hot enough to radiate much. (The corresponding figure for mercury vapor is 10 watts per centimeter.) The "electron temperature" will be on the low side, and most of whatever radiation is produced will be argon's near-infrared wavelengths.

The visual effect of a "stable burnout arc" is usually limited to seeing the gap and bright whiter-color spots at the ends of the filament where the gap is. If the gap is in a narrow tube such as in a linear halogen lamp, you may see some dimming of that area from vaporized filament material darkening the inner surface of the tubing. If you can see anything at all with the filament being so bright. If you have a magnifying lens handy, you may be able to project an image of the gap onto a wall or ceiling.

Of course, if the lamp is shut down, it will not go on again with a gap in the filament.

Stable burnout arcs in linear halogen lamps have a hazard, especially in the 500 watt ones. The arc can overheat the tubing, and the tube may break while pressure is high from being at full temperature. The tubing area closest to the arc may soften and form a bubble that may pop - spewing small bits of extremely hot quartz. This is one reason why halogen lamps with this degree of thermal loading require protective shielding enclosures.

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

Neato ..

Never met one that could carry a tune in a bucket ;-)

Happy Christmas!

-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more durable; the other is a cheaper thing, but the moths get into it." (Stephen Leacock)

Ohhh the gifts get worse every year. :(