Gas leak, Schlieren image. Engineer attending a gas leak. The turbulence of the gas jet has been shown by Schlieren photography, a way of viewing density changes in transparent materials. These changes (here due to the gas turbulence) cause light passing through the gas to bend (refract). The imaging method alters the colour or brightness of this refracted light. Other applications of the method include improving ventilation in the office and home, and detecting chemicals in the human thermal plume. Photographed by the world's only (as of 2003) full-scale Schlieren system, developed by Gary Settles, professor of mechanical engineering at Pennsylvania State University, USA.