Find the external transmittance T 2.2 for a filter that is 2.2 mm thick. When light passes between dissimilar materials, the rays bend and change velocity slightly, an effect called refraction. The index of refraction itself is also dependent on wavelength. This angular dispersion causes blue light to refract more than red, causing rainbows and allowing prisms to separate the spectrum. Diffraction Diffraction is another wave phenomenon that is dependent on wavelength.
Light waves bend as they pass by the edge of a narrow aperture or slit.
This effect is negligible in most optical systems, but is exploited in monochromators. A diffraction grating uses the interference of waves caused by diffraction to separate light angularly by wavelength. Narrow slits then select the portion of the spectrum to be measured. The narrower the slit, the narrower the bandwidth that can be measured. However, diffraction in the slit itself limits the resolution that can ultimately be achieved.