I heard that when sunlight enters house through windows, it gets converted into longer wavelengths and gets trapped inside.
So does the glass have anything to do with this or is this about heated materials radiation, and why does the light get trapped?
Just for completeness, there are some materials that do actually convert the frequency of light. They're called optical frequency converters. These tend to work only on paired photons, and thus are transparent when you look at them, but when you shine a whole lot of one frequency on them it converts up. That allows you to do some interesting things:
In this case the green is being upconverted from the monochromatic red light.
This isn't "glass" so it's not what you're asking, but one could use it in this fashion to, say convert red photons to green on the front of a solar panel and then capture the green photons at higher energy. In theory this is more efficient than capturing the two original red ones. You could, in theory, make a window that upconverted IR to visible and thus better light the room.
Here's how it works. Passage through a piece of glass does not change the wavelength of light. The change occurs when the light strikes objects in the room. Absorbing light energy causes those objects to warm up, and then they begin re-radiating that heat energy at wavelengths which are in the infrared range- which do not pass easily through glass.
Using a particle picture, we note that the interaction between matter and light happens at the electronic level. Electrons absorb energy in acceleration (energy increase) and release (radiate) it on deceleration. In general, this process involves a spectrum of frequencies with the power given in Larmor’s formula for radiation power. Note that this formula contains only even powers of the variables and as such doesn’t differentiate between positive and negative acceleration. In a cathode ray tube, electrons gain kinetic energy from an electric potential field, accelerate then shed this energy as they hit the target screen. The same happens in Cherenkov radiation. In atoms this is slightly complicated by changes in potential energy of electrons at the same time. When high energy light hits electrons in their atomic orbit, it causes them to shift out/up of the potential well they were in and gain energy. Then they would fall in/attracted back and loose this energy. As the process is fast and accurate- depending only on the specific orbits, emitted radiation comes out in a narrow spectrum (line) associated with each orbit. In synchrotron radiation, electrons gain energy and speed via electrical pulses, then subsequently loose it when they ‘decelerate’ as they go round in a loop. We know it is deceleration because it is a forced change of direction by the magnetic field force confining the beam to remain within a circular path. A change in frequency of light happens in matter when the absorption and emission of light happen due to electrons either loosely or tightly attached to molecular structures. Loosely bound electrons as in metals reproduce (nearly with very little delay) the exact copy of what is absorbed due to their light weight/small inertia. When electrons are bound tight (large band gaps), light can pass through matter unaffected as in transparent materials. In opaque matter, light is absorbed by the electrons, energy gets distributed in the structure then emitted via slowly moving electrons within molecules- resulting in a longer wavelength. This is not very different from a large drum receiving energy from various sources but only producing low frequency sound. For more sophisticated crystal structures and their electrons, it is possible to get more than one frequency from a single frequency light input- as in frequency doublers. If light collides with fast moving electrons, it is possible to either decrease or increase the frequency of (x-ray) light as in Compton and inverse Compton scattering.
When light enters a medium of different refractive index (different than through which it was travelling before entering into it, in your example from air to glass) it’s speed changes but frequency doesn’t change as no new light is being created and since
Speed = frequency x wavelength
And frequency is constant, therefore, wavelength must change.
Hope it helps.
