eli5: why does glass absorb infrared and ultraviolet light, but not visible light?
In: Physics
Light is part of a spectrum, meaning rainbow. The colours of the rainbow are just the parts our eye can see, but they stretch beyond red (into infrared) and violet (into ultraviolet). Redder waves are bigger. Purpler waves a smaller.
All of these colours, including the ones our eye can’t see, will behave differently depending on their size. The way that the atoms are arranged in glass mean that the big ones get trapped in the spaces between the atoms. The really small ones get sucked up by the atoms themselves. But light is in the happy middle ground and gets to sneak between the atoms while still being big enough to avoid getting sucked up by them. Visible light therefore can go through it as if there is nothing there.
This happens all over the place. X-rays for example are so small they can even go through the atoms themselves, meaning they are good for seeing through things like fabric and skin – useful for an airport security scanner. Microways are big enough that a metal grid in your microwave oven window is enough to stop them from escaping.
Depends on the glass composition. For instance solar green glass, which is commonly used in automotive applications has a different makeup compared to glass used on a coffee table, or glass used on a skyscraper. Solar green does a nice job blocking some UV and some infrared, and allows for most visible light because that’s what’s required by law and practically what is needed for cars.
All of this can be changed in 3 main ways: change the recipe for the glass, add a piece of laminate between two pieces of glass or add a coating to the glass. That can impact color, light transmission, heat absorption you name it.
Basically light wavelengths have different “distance”/frequency, which we observe as different colours (measured in nm), UV IR etc are not detectable by eye. The wavelengths (“distance”) needs to be identical distance in bonds between atoms or electrons to interact and pass energy (which is why light can heat up materials), if distance is not perfect it just passed through like in case of visible light and glass. Some one check I’m pretty sure it’s correct
A lot of decent explanations of how electrons absorbs photons, but most comments don’t answer OPs original question and many include misinformation.
Glass does not absorb (much) UV or infrared light by default. However, it is common more recently (last 10-15 years) for glass to be manufactured with a “low-e” coating (low emittance). This coating is made of a compound that specifically reflects (like a mirror) infrared and much UV light. Since UV and infrared are invisible to our human eyes, these coatings don’t look like mirrors, they look clear; but if you have infrared vision, they would look shiney.
How does a compound only reflect certain types of light? Many other commenters have attempted to explain and some are correct.
There is actually a lot of empty space in between atoms. Think of the size of an atom as a football field and the nucleus as a football in the center of the field with the electrons as M&Ms orbiting around the field and the stands. That’s a LOT of empty space between individual atoms; plenty of room for photons to slip through!
But how do most materials absorb most light and end up being opaque? Well, photons are absorbed by the electron “orbitals”, NOT by the electron (per se) or by the nucleus. The orbital is just the area within which the electron orbits, and they have weird shapes; it’s very complicated, so lets just imagine that some electrons orbit in the home team goal zone, some orbit in the away team goal zone, and some orbit in the spectator stands.
If a photon passes through the orbital of an electron, the orbital may absorb that photon; the energy of that photon is then transfered into the electron in that orbital. But here’s the thing: not all orbital absorb photons. Some orbitals will let photons pass right through them, others will only absorb photons of certain wavelengths (like UV or infrared).
Why don’t all electron orbitals absorb all photons? That has to do with complex quantum resonance and interactions between fermions (which I don’t fully understand). It also has to do with how many orbitals the atom has, how close they are to being full of electrons, what types of electron bonds they have with surrounding atoms, and many other factors that I can’t fully comment on.
Suffice to say that “low-e” coatings in glass windows are made of a material that researchers discovered that has atoms with electron orbitals that like to absorb (and then reflect) UV and infrared, but which ignore visible light. How fortunate for our energy savings that they discovered this, so that we can see beautiful things through our windows but not over-heat our buildings in the process!
FYI: as my bleached out hardwood flooring and carpeting can attest to, glass does not block UV unless it is treated to do so.
Wavelengths. Wifi is light. Bluetooth is light, radio, everything wireless is light. And to those wavelengths everything is clear like glass. For x rays your flesh is but your bones aren’t.
For different colored glass, the material allows only certain colors through.
Just the composition of it and how it absorbs or reflects certain wavelengths of light. Which is to do with chemistry/quantum physics and how materials interact with wavelengths of light.
A particular matter being transparent for a certain kind of light means that it is physically unable to tap into the energy provided at that the particular frequencies of the radition (“absorption”). Absorption happens when electrons in the matter resonate with the frequency provided. They can only resonate and hence absorb radiation when they are bound with the “right” strenght, like someone sitting on a swing: If you push in opposite directions too fast, the poor person will not move. If you push every other year, they will swing, but not gain energy either. But if you push just at the right times, they will swinger higher and higher… resonance!
Glass is transparent, because its electrons are either too stiffly bound (absorbing UV) or too losely bound (absorbing infrared), but non of them are able to absorb visible light.
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