Questions on Ultra-Violet Light Radiation and Damage

[qwopty99]

Ask them here.

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[IndianaOD]

Hi folks

I have a few questions here that I've always wondered about but really never knew the answer to.

OK - my understanding is that UV light is the type of natural electromagnetic radiation that concerns us with regards to physiological damage it can cause to the eyes.

Q1. Why is is then, that we can't look at the sun through, say, polycarbonate lenses? I'm pretty sure no handbook anywhere says that with 100% UV-blocking lenses (e.g. PC), it's safe to look at the sun. Why then, is damage still going to be caused? My understanding is that PC blocks all wavelengths below 385 nm - so there is no short-wavelength light that passes through.

I also don't believe that photoreceptors can be "bleached out" with overuse - so what is the actual source of damage - unless we're talking about X-ray/cosmic etc. forms of radiation - but I don't think welder's filters and what not (filters that you CAN look at the sun with) protect specifically against all these other types of radiation (and PC apparently blocks "everything" below 385) - they simply seem to be 1/one million transmittance filters. So if photoreceptors can't be damaged with "over use", why then can't we look at the sun with UV-blocking lenses? (not that I would per se...)

Q2: Again with the understanding that UV light is what damages stuff, why is it in rooms where there are no windows and only have light bulbs, colored items get washed-out and bleached over time? i.e. you may have a poster on a wall in a basement room. I was "told" that UV-light is what causes things like posters and paper (and clothes, and toys, and whatever) to become less (color) saturated over time - that the UV-light breaks down the color component molecules of the material. But in rooms where there are no windows, there is no natural UV light source, and artificial forms of light (incandescent, fluorescent) yield minimal if any UV light. So... why do old posters in basement rooms get bleached?


Just some musings. Thanks in advance.

UV energy isn't the only type of energy. Enough of visible light energy can fry anything. Thermal damage is what I would say could do in the retina. Don't forget you have a 60 diopter magnifier sitting in front of the retina.

 

[qwopty99]

Yes that makes sense. It's a good way to look at it.

 

[qwopty99]

Anyone know the answer to the 2nd question?

 

[drbizzaro]

Hi folks

Q2: Again with the understanding that UV light is what damages stuff, why is it in rooms where there are no windows and only have light bulbs, colored items get washed-out and bleached over time? i.e. you may have a poster on a wall in a basement room. I was "told" that UV-light is what causes things like posters and paper (and clothes, and toys, and whatever) to become less (color) saturated over time - that the UV-light breaks down the color component molecules of the material. But in rooms where there are no windows, there is no natural UV light source, and artificial forms of light (incandescent, fluorescent) yield minimal if any UV light. So... why do old posters in basement rooms get bleached?


Just some musings. Thanks in advance.

If there are absolutely no windows, and the posters were never exposed to natural light sources from the sun, then my guess would be that moisture (from the basement) can be the cause.

I think it might have to do with the fact that moisture can carry contaminants and pollutants to another source, and over many years, can degrade the item.

 

[jymezg]

Q2: Again with the understanding that UV light is what damages stuff, why is it in rooms where there are no windows and only have light bulbs, colored items get washed-out and bleached over time? i.e. you may have a poster on a wall in a basement room. I was "told" that UV-light is what causes things like posters and paper (and clothes, and toys, and whatever) to become less (color) saturated over time - that the UV-light breaks down the color component molecules of the material. But in rooms where there are no windows, there is no natural UV light source, and artificial forms of light (incandescent, fluorescent) yield minimal if any UV light. So... why do old posters in basement rooms get bleached?

I looked into this one and I think that oxidation may be a major culprit. Newspapers yellow and age from oxidation, mabey fading is also a result of this?