# Does light intensity affect transparency?

The reason for the transparent nature of glass is that the photons of visible light don't have enough energy for the electrons of glass to absorb and jump to higher energy levels. As a result, the photons are able to pass through the material.

It's all good. Now let's consider this... Suppose there's an opaque material. Opaque to visible light. Now there's a fixed amount of that material. For example, a small plastic cube. It would have a certain number of electrons. Now, if light falls on it, the electrons will absorb the photons and the object will appear opaque. So far, so good. Now, suppose the intensity of light is increased. This would mean that the number of photons will be increased. But the plastic cube would still possess the same number of electrons as before. So my question is, would the extra photons be able to pass through the material and make it appear transparent or maybe translucent? I mean, the electrons will absorb some photons but since the intensity is increased, there will be a lot more extra photons to get through the material.

Now, what I've hypothesised above clearly doesn't happen.. or does it?? Lol. Anyways, I'm quite sure it doesn't. So I'd like to know the fault in my line of reasoning. I hope it's understandable.

• I'm no physicist but I don't think any object is fully opaque and if you shine a bright enough light on it you'll be able to see some of the light coming out the other side May 7, 2022 at 5:53
• The term you want to Google is "saturable absorber". May 7, 2022 at 6:01

I would like to expand a little on your reflections in the first paragraph. This is important for your second paragraph.

The reason for the transparent nature of glass is that the photons of visible light don't have enough energy for the electrons of glass to absorb and jump to higher energy levels. As a result, the photons are able to pass through the material.

1. When two laser beams cross, they do not interact. However, if this happens in a glass body, then you can generate so much heat at the point of intersection that the glass changes its structure at that point and becomes opaque. This suggests that the interaction of photons with the amorphous glass structure is more complicated than the obvious reduction to energy jumps of electrons that do not occur.
2. Moreover, transparency has not only to do with the (im)possible excitation states of the electrons, but also with the amorphous structure of glass. it is enough to change the smooth surface structure of the glass and the glass becomes opaque and less translucent.

Suppose there's an opaque material… For example, a small plastic cube… Now, if light falls on it, the electrons will absorb the photons and the object will appear opaque.

Opaque means not-transparent in English colloquial language. But you attribute the property of opacity to your plastic cube. This is the dimming of radiation when it passes through a body.
The plastic cube remains opaque to humans up to a certain amount of radiation. With a larger amount of radiation, our eyes then see part of it through the cube.
In both cases, some of the photons are transformed into thermal radiation and some leave the cube with the same wavelength.

Now, suppose… the number of photons will be increased. But the plastic cube would still possess the same number of electrons as before… Would the extra photons be able to pass through the material and make it appear transparent or maybe translucent?

As described above, both processes of conversion into thermal radiation and the transition of photons always take place. With an increasing amount of energy, the electrons are excited more strongly and there is increased heat radiation. In the end, you melt the cube.

• Hi Holger, do you have a link to any articles about "lasers intersecting in glass and turning opaque"? Thanks Aug 5, 2023 at 18:46
• Bill, does this is helpful?: en.wikipedia.org/wiki/Bubblegram Aug 6, 2023 at 3:51