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Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
The short version is I discovered that my old CRT TV emits enough UV light to make a tennis ball fluoresce, I checked this by looking for the security features in a 5$ bill, they also fluoresced. If any of you have a CRT TV try it out, the screen was all blue (the default for no input) and post here if you see the same thing.
Have any of you noticed this? I'm surprised that I've only just seen this now after 2 decades of using CRTs.
Registered Member #3918
Joined: Sun May 29 2011, 08:42PM
Location:
Posts: 34
Strange. From what I understand it's hard to make UV from phosphors on purpose, never mind producing it as a byproduct. Maybe it's just the large amounts of blue light, I had a 1W 445nm blue laser that could make near enough anything fluoresce while not technically being UV.
I don't own a CRT anything so I can't try it out, interesting though.
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
I was under the same impression which is why I was so surprised. I thought maybe the tennis ball had some weird blue fluorescing dye in it but the orange/yellow security fibres in the money makes me think it is actually UV.
Hm, my TV doesn't have a blue screen, rather a screen of static or a black screen. I shall check this out later, but I have no idea how to. I don't have dollar bills or I don't have a tennis ball. I do however have a fluorescent shirt so, I might use that.
Registered Member #3888
Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649
The absorption spectrum of the fluorescent dyes covers a whole region of wavelengths (hence spectrum.) A dye who's peak absorption is in the UV could easily include blue wavelengths in the tails of its absorption curve. I've also seen dyes with several absorption peaks scattered about the visible/near visible spectrum.
So hopefully the CRT isn't actually outputting any UV (that would be bad for the eyes I imagine) and it's just the blue and violet wavelengths that are causing your dyes to fluoresce. Very good observation though.
and as a joke: A UV outputting TV would cause half tanned couch potatoes.
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
Thanks guys, I knew the phosphors put out a wide spectrum but I never thought to look up the absorption spectrum of the security fibres. I'll have to see if I can replicate this with an LCD or LED screen.
*Edit* Derp, it does work with my LCD, mystery solved.
Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
yeah, some backlights use Near UV LEDs (NUV) and a white phosphor layer underneath the screen. This way the emitted light is unidirectional and plane polarised allowing for less energy to be wasted.
Come to think of it, I always wondered why they don't just use an array of UVLD's as they emit a lot more light per watt than LEDs and are polarised for good measure. This also allows the same panel to be used in transflective and transmissive mode with a single polariser on top, much like the Pixel QI panel does.
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CTR screens and UV light (audience participation requested)
