Liquid crystals change color with temperature in the visible region.
We have successfully produced liquid crystal screens that determine the temperature of the air flow field around the outlet from diffusers. This temperature field is characterized by variable colors of the liquid crystals sprayed on the screen. One problem encountered with liquid crystal screens is that the color changes can be somewhat subtle and are masked by variations in color intensity. We have applied image enhancement techniques to solve these problems and are now able to use a video camera and a computer to produce images that clearly show the flow field in the room. This liquid crystal technology has been used to test products from a number of diffuser manufacturers.