The colours are generated by the combination of three circumstances:
- There is polarized light behind the window
- The window is made of a double refracting matter
- A polarization filter is used in front of the window
Under these circumstances, the light gets split up into two coherences of polarized components which travel through the window at different speeds. This causes a phase difference the amount of which depends from the wavelength. This means that the polarization gets transformed once into a linear polarization of a different direction than the origin for a certain colour, and into a circular polarization for another colour (Lissagiu interference of two waves). As the polarization is now dependent from the colour, the colours appear when a polarization filter is used, no matter if this filter is placed in front of the eye or in front of a camera.
These colours can be seen and photographed under the following circumstances:
- There is polarized on one side of the window coming from the blue sky (Rayleigh scattering) and reflection from water and the scattering caused by clouds
- The window is made of plastic. In this material there are mechanical tensions which cause a double refraction.
- There is a polarization filter in front of the camera.
The last condition is not necessary if you look at the window from an acute angle. Then the light becomes already polarized by the refraction. In this case there is no filter necessary to see the colours. However, the colours you can see under this circumstance are fainter than the colours seen through the polarization filter because refraction polarizes only a part of the light.