Schlieren

High Quality Content by WIKIPEDIA articles! Schlieren are optical inhomogeneities in transparent material not visible to the human eye. Schlieren physics developed out of the need to produce high-quality lenses void of these inhomogeneities. These inhomogeneities are localized differences in optical path length that cause light deviation. This light deviation is converted to shadow in a schlieren system. Schlieren flow visualization is based on the deflection of light by a refractive index gradient The index gradient is directly related to flow density gradient. The deflected light is compared to undeflected light at a viewing screen. The undisturbed light is partially blocked by a knife edge. The light that is deflected toward or away from the knife edge produces a shadow pattern depending upon whether it was previously blocked or unblocked.