# Why can't light pass through to the dark side of a window?

• danHa
In summary, the conversation discusses the effects of light on the visibility of reflections through a window. It is stated that the eye adapts to the amount of light coming in, so the reflection is more visible when there is less light. It is also mentioned that about 4% of light is reflected at each glass/air boundary and the formula for this is given as ## \left( \frac{n-1}{n+1} \right) ^2 ##, where n represents the refractive index.
danHa
if I would look through a window on darker area I would see my reflection instead of the outside world . but if the other side of the window is light then the light may pass through the window does the light outside effect the window and make the refraction disappear ?.
or the light always cross both window side but our eye filter the reflection when more light is coming outside ?.
what happens if I point laser from two side of the window in difference angles on the same point would only one laser come trough the window ?.

Last edited:
danHa said:
or the light always cross both window side but our eye filter the reflection when more light is coming outside ?.
Yes. The eye adapts to the total amount of light coming in, so you see the reflection better if there is less light coming trough the window.

danHa
The reflected and transmitted images are always there. Your eye picks up the brighter image and ignores the dimmer one - it may not even be able to detect the dimmer image if the brighter one is too bright.

Sometimes the brightnesses of the two images are comparable and you can see both. You can probably see this if you live in a built up area - turn on a light inside after dark and look out at the street. You'll probably be able to see both your reflection and the outside world.

A rule of thumb (from 20 year old memory, so beware!) is that about 4% of light is reflected at each glass/air boundary. So your side needs to be quite a lot brighter than the other side for you to see a reflection.

Redbelly98, vanhees71 and danHa
Ibix said:
A rule of thumb (from 20 year old memory, so beware!) is that about 4% of light is reflected at each glass/air boundary.
Correct. Generally 3.5% to 4%, depending on the specific type of glass.

The formula is ## \left( \frac{n-1}{n+1} \right) ^2 ##.

danHa, Keith_McClary and Ibix
A.T. said:
Yes. The eye adapts to the total amount of light coming in, so you see the reflection better if there is less light coming trough the window.

Redbelly98 said:
Correct. Generally 3.5% to 4%, depending on the specific type of glass.

The formula is ## \left( \frac{n-1}{n+1} \right) ^2 ##.
what n stand for?

Redbelly98, danHa and Ibix

## 1. Why does light not pass through to the dark side of a window?

Light does not pass through to the dark side of a window because of the property of materials called opacity. Most materials, including glass, have atoms that are tightly packed together, making it difficult for light to pass through. This results in most of the light being reflected or absorbed by the material, causing the dark appearance on the other side of the window.

## 2. Can any type of light pass through to the dark side of a window?

No, not all types of light can pass through to the dark side of a window. The ability of light to pass through a material depends on its wavelength. Visible light, which is the type of light that we can see, has a shorter wavelength and is able to pass through glass. However, longer wavelengths of light, such as infrared and ultraviolet, are unable to pass through most types of glass and are absorbed or reflected instead.

## 3. Is there any way to make light pass through to the dark side of a window?

Yes, it is possible to make light pass through to the dark side of a window by using special types of glass called transparent or translucent glass. These types of glass have a different molecular structure that allows light to pass through with minimal absorption or reflection. However, even with these types of glass, some light may still be absorbed or reflected, resulting in a slightly darker appearance on the other side of the window.

## 4. Why does light pass through some materials but not others?

The ability of light to pass through a material depends on its molecular structure. Materials with tightly packed atoms, such as glass, have a high level of opacity and do not allow light to pass through easily. On the other hand, materials with loosely packed atoms, such as air or water, have a lower level of opacity and allow light to pass through more easily.

## 5. Can light pass through to the dark side of a window in a vacuum?

No, light cannot pass through to the dark side of a window in a vacuum. A vacuum is a space with no particles, including air molecules, which are necessary for light to pass through. Without any particles to interact with, light cannot travel through a vacuum and would simply continue in a straight line until it reaches an object or surface that it can interact with.

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