When the critical angle is exceeded for a particular wave, it exhibits total reflection back into the medium. This concept is important in optical microscopy and will be discussed in greater detail in our discussion on immersion media in the Anatomy of the Microscope section of the Microscopy Primer. Another important feature of light refraction, as discussed above, is that the wavelength of light has an impact on the amount of refraction in the same material. The amount of refraction is inversely proportional to the wavelength. Thus, shorter wavelength visible light is refracted at a greater angle than longer wavelength light.
White light is composed of all the colors in the visible spectrum.
When this light is passed through a glass prism, the white light is dispersed into its component colors in a manner that is dependent upon the individual wavelengths. Dispersion is also responsible for chromatic aberration, an artifact resulting from refractive index variation with wavelength. When white light is passed through a simple convex lens, several focal points arise in close proximity that correspond to the minor refractive index differences of the component wavelengths. Correction of this aberration is accomplished by the use of combinations of two or more lens elements composed of materials having different dispersive properties. A good example is an achromatic lens constructed with both crown and flint glasses.