# Looking through glass

1. Jan 31, 2006

### physicsss

If light reflects from all surfaces, why is the view through a glass window not noticeably dimmer than the view with the window open?

Can someone give me som hint? I know glass has a refractive index of 1.5...

2. Jan 31, 2006

### Mk

The glass does not absorb very much light, and does not reflect very much light.

A strawberry absorbs wavelength's other than red. That is why it looks red to you.

A black object absorbs most of the light that comes at it, so it looks black.

3. Feb 1, 2006

### ZapperZ

Staff Emeritus
Ordinary glass DOES absorbs light, espeically in the UV range. We pay a lot of money to get quartz and fused silica to let UV light passes through. There's no material that I know off that lets light of all frequency to pass through.

Zz.

4. Feb 1, 2006

### fargoth

this is fresnel relaction, as you can see the percent of reflection is very small.

$$R=(\frac{n_1-n_0}{n_1+n_0})^2$$

but this is just the classical vies of things, (its pretty accurate, but feyman got it better)

Last edited: Feb 1, 2006
5. Feb 1, 2006

### pallidin

It IS dimmer, just not necessarily "noticable" through "human" eyes. I know of no glass(or any substance for that matter) that transmits light with no loss.

6. Feb 1, 2006

### Claude Bile

Our eyes are logarithmic detectors - that is, they are capable of measuring light intensities over many orders of magnitude. As such, a 4% change in intensity (typical for air-glass reflection) is not readily apparent to the naked eye, as it would be for a linear detector such as a photodiode.

Claude.

7. Feb 1, 2006

### Manchot

I guess that's why I can't get a tan through the window...:tongue2:

8. Feb 2, 2006

### bomba923

Why would we want glass to transmit UV?
Don't we want to protect ourselves from UV radiation? (it may cause sunburn! )

9. Feb 2, 2006

### Mk

10. Feb 2, 2006

### ZapperZ

Staff Emeritus
I have a laser that is in the UV range. But my experiment is done in ultra-high vacuum. I'll give you ONE guess on why I would need a fused silica window somewhere on my vacuum chamber.

Zz.

11. Feb 2, 2006

### DaveC426913

The Newtonian telescope is based on the fact that glass does absorb light.

A Newtonian is different from other types of telescopes in that it uses mirrors rather than lenses. Every lens the light passes through costs you a fraction of precious, precious brightness, which is what astronomy is all about.