OT:Incandescent "soft white" bulb coating?

Jan 21, 2005 5 Replies

First reply

Sylvan Butler

Doesn't stuck much... Even the broken pieces of filament swirled around inside the bulb scrape off the powder. Hopefully it is just some talc, gypsum, ... sdb

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Not exactly an electronics question, but I know some lighting gurus hang out here. (Google hasn't been any help so far.)



What is the stuff used as the coating on typical incandescent "soft white" bulbs? I gather that the non-soft-white are simply acid etched on the inside of the envelope, but the soft white have a separate powder applied somehow. What is this stuff chemically? What makes it stick? (It seems pretty fragile if you touch it on a broken envelope piece.)



Thanks!


Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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Doesn't stuck much... Even the broken pieces of filament swirled around inside the bulb scrape off the powder. Hopefully it is just some talc, gypsum, ...

sdb

Wanted: Omnibook 800 & accessories, cheap, working or not sdbuse1 on mailhost bigfoot.com

All I know is that at least in flourescant lights they use different shades of colored phosphors. I would imagine it's the same stuff but I don't know.

The two commonly used finishes inside are etched glass (frosted) and applied silica powder. As I said, the etched glass is known as 'inside-frosted' or simply 'frosted' and results in the appearance of a glowing ball of light within the globe. But silica powder is also used, and called 'soft-white' by most major manufacturers. Although this cuts output more than etched glass, it makes the entire bulb glow more evenly.

I hope this helps some.

Jon

Thanks, Jon, this is exactly the sort of info I was hoping for. Any idea what makes the silica stay on the inside of the envelope?

Thanks again!

Bob Masta dqatechATdaqartaDOTcom D A Q A R T A Data AcQuisition And Real-Time Analysis

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No, but I honestly haven't tried to fathom this in any detail. I don't either have theory or experimental data to suggest much to me.

If you have a bulb to break open, see how well you can clean the substance off with your fingers or wet rag. If it all comes off easily, then it is probably surface tension and possibly some frosting on the inside to encourage that tension and the particles are probably "very, very tiny." Otherwise, maybe they "use something." But my bet would be that they would avoid depending on anything other than the silica -- the more that is added, the higher the cost (especially, as it is hard to find higher-temp materials and deal with outgasing, etc.) and the more dangerous it may be in the home, as well.

But I just don't know.

Jon

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