Anti reflective coatings are used to maximise the amount of transmitted light at a glass interface. It does this by causing reflected light to undergoes destructive interference as much as possible.
As shown blow, if the glass is coated with a layer such that the thickness of the layer in
then light reflected at the coating layer interface
and the coating glass interface
has a path difference of
and destructive interference occurs.
Of course complete destructive interference will only occur for a single wavelength. Because visible light is made up of a range of wavelengths, this will mean that the reflected light appears tinged with colour – the phenomenon known as 'blooming'.