Properties:

A light transmitting item consisting of a transparent, flat glass body having two plane-parallel surfaces, either with only nonabsorbing dielectric coatings or absorbing and nonabsorbing coatings of a thickness nearly equivalent to the wavelength of the transmitted light. Interference begins at the thin bordering surfaces of the coatings, the penetrating light waves being superimposed on the reflected light waves. The item can be installed in various optical insturments, to serve as an eye protecting device.