Photo Chromic Spectacles

[silverback]

I have a pair of photochromic spectacles with Kodak InstaShade lenses.
I have always understood photochromic lenses darken when exposed to ultraviolet light; also, I have always understood that glass is a barrier to UV light.

If I put this pair of spectacles on a table and they are exposed to sunlight shining through a window, they go dark.
Obviously, one of my 'understandings' above is incorrect. As the Kodak website says they darken in response to UV light, it must be the assumption that glass stops UV.
So. Is it really possible to get sunburnt from sunlight coming through a window?
Thanks
Silverback

[HansV]

What do you see if you put them on and stand at a sunlit window? And does it make a difference if you open the window?

[StuartR]

Ultra violet light can pass through glass, depending on the light frequency and the exact type of glass.

See for example
http://www.newton.dep.anl.gov/askasci/g ... n06495.htm" onclick="window.open(this.href);return false;
or
http://www.aad.org/media/background/new ... s_and_Out/" onclick="window.open(this.href);return false;

[viking33]

I have a pair of photochromic spectacles with Kodak InstaShade lenses.
I have always understood photochromic lenses darken when exposed to ultraviolet light; also, I have always understood that glass is a barrier to UV light.

If I put this pair of spectacles on a table and they are exposed to sunlight shining through a window, they go dark.
Obviously, one of my 'understandings' above is incorrect. As the Kodak website says they darken in response to UV light, it must be the assumption that glass stops UV.
So. Is it really possible to get sunburnt from sunlight coming through a window?
Thanks
Silverback

Glass does not block UV light. Just as some "sunglasses" do not block UV. Photochromic glasses go dark in response to UV in order to lessen the effects of UV, not block it.

[silverback]

What do you see if you put them on and stand at a sunlit window? And does it make a difference if you open the window?

With the window shut, the spectacles go a little dark but they are much darker when the window is open. This is entirely consistent with the data in the articles given in the links in Stuart's posting.

I am truly shocked, though, that it is possible to get body parts sunburnt whilst travelling in a car with the windows raised (unless the side windows have a special coating).

Thanks to everyone for replying.
Silverback

[steveh]

What do you see if you put them on and stand at a sunlit window? And does it make a difference if you open the window?

With the window shut, the spectacles go a little dark but they are much darker when the window is open. This is entirely consistent with the data in the articles given in the links in Stuart's posting.

I am truly shocked, though, that it is possible to get body parts sunburnt whilst travelling in a car with the windows raised (unless the side windows have a special coating).

Thanks to everyone for replying.
Silverback

My evidence is purely anicdotal but quite a few years ago we took my daughter of about 23 then to Malta, the temperature was in the high 30°C's and she felt ill. We went out for the day and she stayed all day in the room. When we got back she was in a terrible condition with sunburn but had not left the room all day

[PJ_in_FL]

I am truly shocked, though, that it is possible to get body parts sunburnt whilst travelling in a car with the windows raised (unless the side windows have a special coating).

A very high percentage of skin cancer cases occur on the left arm in the US and drive-on-the-right-hand-side-of-the-road countries. That arm gets exposed while driving, and, as you noted, glass doesn't block most UV wavelengths.