Why does light intensity decrease when light passes through a glass block?

In summary: Hi Guys,I am new to this forum and have a "quick" question.Say you had a laser pointer and you directed the laser through a glass block and then to a LDR why would the light intensity recorded be lower than without the glass block? What is happening to the light when it is in the glass? And why does making the glass thicker make the light intensity decrease even more?Thanks a lot.Oli.The glass scatters light out of the beam direction. Unless you are working with optical-quality glass, glass is fairly heterogeneous. Even so, 'perfectly manufactured' glass is oh-so-slightly absorptive. Indeed, the best glass for optical
  • #1
Zebadee
3
0
Hi Guys,

I am new to this forum and have a "quick" question.

Say you had a laser pointer and you directed the laser through a glass block and then to a LDR why would the light intensity recorded be lower than without the glass block? What is happening to the light when it is in the glass? And why does making the glass thicker make the light intensity decrease even more?

Thanks a lot.

Oli.
 
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  • #2
I'm guessing that the some of the particular photons will have energies corresponding to vibrational modes in the glass (lattice, electronic, molecular, etc). So each time that happens, some light is absorbed.
 
  • #3
So the glass actually absorbs some of the light?
 
  • #5
Thank you very much, I will give this a good read.
 
  • #6
Increasing the thickness of a glass layer would increase losses due to absorption and scattering since both are dependent on length.

You also get Fresnel reflections, which is about 4% of the incident light reflected per interface for glass.

Claude.
 
  • #7
Zebadee said:
Hi Guys,

I am new to this forum and have a "quick" question.

Say you had a laser pointer and you directed the laser through a glass block and then to a LDR why would the light intensity recorded be lower than without the glass block? What is happening to the light when it is in the glass? And why does making the glass thicker make the light intensity decrease even more?

Thanks a lot.

Oli.

the glass scatters light out of the beam direction. Unless you are working with optical-quality glass, glass is fairly heterogeneous.

Even so, 'perfectly manufactured' glass is oh-so-slightly absorptive.

Plot the intensity as a function of glass thickness- it should be exponential (Beer's law)
 
  • #8
Andy Resnick said:
Even so, 'perfectly manufactured' glass is oh-so-slightly absorptive.
Indeed, the best glass for optical transmission (silica optical fibre) has losses of about 0.1 dB per km, most of which is due to absorption.

Claude.
 

1. Why does light intensity decrease when light passes through a glass block?

Light intensity decreases when passing through a glass block due to the process of refraction. When light enters the glass, it changes speed and direction, causing some of the light to be reflected and some to be transmitted. This results in a decrease in the overall intensity of the light.

2. How does the thickness of the glass block affect the decrease in light intensity?

The thicker the glass block, the more light is absorbed and scattered, leading to a greater decrease in light intensity. This is because the light has to travel a longer distance through the glass, giving it more opportunities to be absorbed or deflected.

3. Does the color of the glass block impact the decrease in light intensity?

Yes, the color of the glass block can affect the decrease in light intensity. Darker colors tend to absorb more light, resulting in a greater decrease in intensity compared to lighter colors. This is due to the absorption of certain wavelengths of light by the molecules in the glass.

4. How does the angle of incidence affect the decrease in light intensity?

The angle of incidence, or the angle at which light enters the glass block, can impact the decrease in light intensity. When light enters the glass at a steeper angle, it has to travel through a greater thickness of glass, resulting in a larger decrease in intensity.

5. Is the decrease in light intensity the same for all types of glass?

No, the decrease in light intensity can vary depending on the type of glass used. Different types of glass have different refractive indices, which affects how much the light is bent and scattered as it passes through. For example, a glass block made of lead crystal will cause a greater decrease in light intensity compared to a regular glass block.

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