Lumen maintenance and spectrum maintenance

shrubs_n_bulbs(z8/9 UK)February 25, 2005

I was looking at a new and an old bulb today and the old bulb was noticeably dimmer. They were actually reflected off glass because they both just look glaring white bright directly. I took somemeasurements and the old bulb was roughly 15% dimmer.

So far so good, fluorescent bulbs get dimmer as they get older. What is interesting is that it also looked redder. Side by side, the old bulb had a distinct orange cast. Maybe that was just my eyes seeing more red in the dimmer bulb. Or had the spectral output actually changed? Do blue phosphors degrade faster?

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jkirk3279(Z5 SW MI)

Bulbs don't have blue phospors per se. Televisions DO. Bulbs don't.

What may be causing the effect is that blue light is more energetic. As the 'heater' in the end of the bulb wears out, it's got less umph and isn't pushing the bulb as hard as it once did.

So you get light that's not only less intense, it's biased toward less energetic wavelengths like red rather than blue.

How florescent tubes work: a current of electricity passes through the bulb, traveling through mercury vapor. This releases light in the UV spectrum. That's useless to us, so the inside of the bulb is coated in some fairly nasty phosphorus.

This coating absorbs the UV light and floresces in light we can use.

By the way, if you ever break a tube, don't inhale that dust. You've heard of Heavy Metal Poisoning ? As in Mercury ?

Well, you can get Light Metal Poisoning too. Phosphorus is a 'Light Metal'. And it's not healthy at all.

Or as my Physics Professor in College said " it's a bad actor."

    Bookmark   February 27, 2005 at 10:06PM
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shrubs_n_bulbs(z8/9 UK)

Please click on the link to see a blue phosphor. It is a standard component of modern triphosphor fluorescent tubes. If you like, you can click on the blue phosphor to see some specs, including the chemical formula (no mercury and no phosphorus!) and an emission spectrum.

Phosphorus is not a metal. The element is highly reactive, can spontaneously combust in air, and so is quite dangerous. It is usually found in phosphate form which is not particularly dangerous as such. Phosphates are in everyday use for such things as fertilisers, detergents, and fluorescent phosphors :)

Here is a link that might be useful: Triphosphor phosphors

    Bookmark   February 28, 2005 at 5:22AM
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jkirk3279(Z5 SW MI)

Well, that's embarrassing.

I had always remembered Phosphorus as a metal. Instead, it's a non-metal like sulphur.

"you can click on the blue phosphor to see some specs, including the chemical formula (no mercury and no phosphorus!) and an emission spectrum."

I think in this case 'phosphor' is being used as a generic term.

The original florescents used phosphorus.

Here is a link that might be useful: Mercury Disposal

    Bookmark   March 2, 2005 at 6:11PM
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shrubs_n_bulbs(z8/9 UK)

Sorry Sam. I didn't mean to imply that fuorescent tubes don't contain any mercury and phosphates. They obviously contain mercury in vapour form since this is the primary source of the light, although modern tubes only contain about a tenth of the amount that they used to. There are still plenty of halophosphor tubes in which the phosphor is made entirely from calcium chloro-fluoro-phosphates, but the modern triphosphor tubes contain almost no phosphates. That particular blue phosphor, for example, is made from rare earth metals but no phosphates.

The danger of broken fluorescent tubes is virtually negligible despite the numerous publications about how hazardous they are. The phosphor chemicals are pretty insert and non-toxic. They are certainly not acutely toxic so unless you are in the habit of breaking a tube every day to inhale a bit of dust then there is no danger. Mercury is a toxic substance, partly because it is expelled from the body so slowly, and partly because it is persistant in the environment. But the quantity of mercury in a fluorescent tube simply isn't high enough to cause health problems. Again, don't make a habit of it, but don't panic at the sight of a broken tube. Disposal of fluorescent tubes in quantity is an issue, but the biggest danger of a broken fluorescent tube in the home is getting glass in your foot :)

    Bookmark   March 3, 2005 at 9:13AM
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