# Why only plane polarized light is absorbed in polarized glasses?

Polarizing glasses can cancel out the light that is reflected from either the horizontal plane or the vertical plane. But why it can not cancel out the light that is reflected from the perpendicular plane?

A typical polarizing filter contains light-absorbing molecules that are long and thin, all oriented in one direction. An individual molecule is electrically conductive along its length, so absorbs light whose electric field vector is oriented in the direction of the molecule's length. Light that is plane-polarized with the electric field in that direction is absorbed, while light plane-polarized in an orthogonal direction is not absorbed.

Any light that can be represented as consisting of two plane-polarized components (e.g., light whose polarization is circular, elliptical, or random) is converted to linearly polarized light by passing through that kind of polarizing filter. The light that emerges from the filter is all plane-polarized in the direction orthogonal to the absorption axis of the filter.

It is interesting to note that light polarized at 45 degrees to vertical can be considered to contain two components polarized in the vertical and horizontal directions. So, light polarized at 45 degrees is only partly absorbed by a polarizing filter that absorbs at 0 degrees: light emerges that is polarized at 90 degrees.

Light that reflects at an angle of about 54 degrees away from normal from a smooth glass (or plastic, water, or even stone) surface is polarized with its electric vector parallel to the surface. So, in your photo light reflected from the tabletop has horizontal polarization, while light reflected from the vertical surfaces has vertical polarization. So, if you tip your head 90 degrees, or rotate your polarizing glasses 90 degrees, you will find that reflections from vertical surfaces will be absorbed while reflections from horizontal surfaces will be transmitted. Light that is reflected multiple times can have its polarization direction rotated to almost any angle.

• OK, so a polarizing filter has either vertical or horizontal lines of molecules that absorbs light that is plane polarized. Now my question is, do these lines of molecules even absorbs the unpolarized light that has electric field vector oriented in the same direction or they don’t?
– user248881
Commented Dec 31, 2019 at 0:37
• If you pass randomly polarized (i.e., unpolarized) light through a good absorbent polarizing filter, the filter absorbs a large percentage of the light, and only light of one polarization emerges from the other side of the filter. Note that there are also polarization filters that are not absorbent, and instead divert light of orthogonal polarizations into different directions. Commented Dec 31, 2019 at 1:40
• If you could take a slow motion video of unpolarized light, you would see that at any moment it is polarized, but that the polarization direction changes randomly and very rapidly. A linear polarizing filter does what it is supposed to do, absorbing any component of the light whose polarization happens to be aligned with the absorbent axis of the filter. Commented Dec 31, 2019 at 1:49
• So if a polarizing filter is absorbing even the unpolarized light, then why it don’t shows any difference? I mean, when it absorbs ‘glare’ (plane polarized light), we can clearly see as the glare almost disappears; but nothing much happens when it absorbs to unpolarized light. Can you explain me why?
– user248881
Commented Dec 31, 2019 at 5:48
• I'll try to explain by analogy. Suppose only red light reflected from vertical surfaces, and only green light from horizontal surfaces. Switching between red and green filters would show obvious differences in a scene. But suppose all surfaces were white so they reflected all colors equally. Then switching between filters would either turn the whole scene red or the whole scene green. Red or green filters would not make vertical and horizontal surfaces look different. Analogously, a linear polarizer dims all unpolarized light equally. Commented Dec 31, 2019 at 12:55