SPIE Proceedings Vol. 4021

Technology for electronically varying helmet visor tint


Increasing interest in helmet-mounted displays (HMDs) has fueled research in variable transmittance visors (VTVs) because a VTV can reduce glare and increase HMD contrast in bright lighting conditions. The ideal VTV will be an electrically controllable light valve that allows the pilot to adjust visor transmittance (tint) to the level appropriate to the ambient lighting conditions. Liquid- crystal based devices can provide an efficient method for accomplishing this. Because flight helmets utilize polycarbonate visors, VTVs must be implemented on complex curved, plastic substrates. Liquid crystal devices, however, are typically implemented on flat glass substrates. We present a novel system, Variable Attenuation Liquid Crystal Device (VALiD), which can be utilized for this application. VALiD is a dichroic dye and liquid crystal based guest-host system. Our specific configuration allows for a fast system that fails to the clear state. Furthermore, the degree of polarization dependence can be tailored for use in different applications. VALiD has been implemented on thin, flexible, flat plastic substrates. Recently, this has been extended to doubly curved polycarbonate substrates and a prototype has been fabricated. In this paper we present the characteristics of this technology.