# Absorbance of UV light by glass

1. Sep 19, 2009

### N0b0dy

Hi, I'm doing an investigation into the absorbance of UV light by glass of varying thickness (constant density and standard type of glass) for an assigment. However, we're not actually supposed to carry out the investigation due to time constraints, so we're meant to make up the numbers ourselves. This would be easy if I was doing a topic such as projectile motion. However, in this case I have literally no idea what figures I should include. Could anyone please help get me started by suggesting some increments of glass thickness that would demonstrate a particular relationship? I assume the graph (absorbance % against glass thickness) would plateau off at a certain point because I've heard many people say that you can still be sunburnt no matter what kind of glass it is.

2. Sep 19, 2009

### MATLABdude

Since this is homework, rather than give you the answer, I'll just give you a few hints:

The Beer-Lambert Law, or Beer's Law, or a few other permutations deals with absorption of light through a medium as the light passes through said medium:
http://en.wikipedia.org/wiki/Beer-Lambert_law

You'll note that one of the formulations involves the absorption coefficient $\alpha$ which is elaborated on further down in the article. Part of that elaboration is the extinction coefficient $\kappa$.

The extinction coefficient of some glasses (including plain-jane soda lime glass) is given here (no idea whether or not they're right, however):
http://www.colostate.edu/orgs/SEAL/research/IAM/iamv2/manual.txt [Broken]

Keep in mind that this is probably for a visible colour, and when dealing with real glass and UV light, the approximation given for absorption coefficient is probably going to differ a fair bit from the 'real' value (which I can't easily find anywhere on the internet)

EDIT: Disclaimer, I am not an optics guy.

Last edited by a moderator: May 4, 2017
3. Sep 19, 2009

### N0b0dy

So there's not really any practical way of working this out unless I actually carry through with the experiment? This is high school standard so I assume I don't need to go into such great detail. Could anyone provide me with a hint as to when the absorbance plateaus off which I can base my 'results' on?

Last edited by a moderator: May 4, 2017