I thought UV is invisible.

why do the UV tubes glow?

is it the chemical they have...like the stuff in invisible ink?

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You shouldn't need to change a MVB until it dies, at least that's what I've been told by owners of UV meters, they apparently decay by around 30% over their lifespan, but even 70% of the original output is still way more than most new tubes!

Because they also give out visible light, UV is only a percentage of the total output, UVA usually around 30%, UVB whatever % the tube is rated, and the rest visible light.

Gotcha.

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I was told that the bulb wouldstill emit light even if its UV ran out.

true?

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I suppose that may be possible as they have two elements, a normal tungsten filament that produces heat/visible light, and a quartz arc tube that produces UV.
As I understand it the tungsten filament also doubles as the ballast required to regulate the tube, so if the tungsten filament blew then the lamp would stop working completely, but I'm not sure if the tungsten filament would keep working if the tube blew?
I guess you'd notice the difference though if it was no longer producing UV, the colour would be quite different.

right, I'll look out for any colour changes. Cheers.

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Yes they still produce light and they still produce uvb, it's just that it does not reach it's target any more as during the life of the tube it produces a milky coating on the inside of the tube, which we cannot see but prevents the rays from getting through

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Take care
Sue

www.tortsmad.com
wizzasmum@aol.com

Loads of UV tubes have little pop out bits for you to write they date onto because they say you need to change them every 6 months.

Oh, thats usefull

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