English: Principle of Interference Reflection Microscopy (IRM) showing interference effect on reflected wave fronts and the result on the final image intensity. Bright green wave represents the polarized light from the light source. The darker green waves are the reflections from the cell membrane, the blue waves the reflections from the glass surface. If the membrane is close to the glass, the reflected waves are shifted about half a wavelength (see red line) and will cause interference, resulting in a dark pixel. If there is more distance between the membrane and the glass, the returning waves will be less shifted and won't cause interference, resulting in a brighter pixel in the final image. Indicated are the typical refractive indices of the glass, medium and the cell membrane, which determine the amount of reflection.