Variable Transmittance Visor Development Program.

This projects objective was to develop a technology for varying the transmittance of conventional flight helmet visors under electronic control for the purpose of enhancing the contrast of helmet mounted displays. The specifications required a 101 attenuation range with a clear-state transmittance of 70 or better and no visible coloration, haze, or optical distortion. Two technologies were studied polymer dispersed liquid crystal PDLC and suspended particles. Several low birefringence PDLCs with neutral dye in a guest-host arrangement were tested they produced excessive haze, apparently because their birefringence, although relatively low, was still too high for the projects purpose. The suspended-particle technology was tested in two forms fluid and polymer-dispersed. Both forms showed a strong blue coloration in the dark state and neither proved to be compatible with conventional visors instead, they must be sandwiched between mating halves of custom-built visors. Furthermore, over time, the fluid form developed streaks and dark spots the polymer-dispersed form developed crazing lines and spatial non-uniformities. We conclude that the suspended-particle technology is not promising, but guest-host PDLC deserves further exploration if PDLCs having lower birefringence become available. MM