HMD daylight symbology: color choice and luminance considerations

As the military increases its reliance upon and continues to develop Helmet Mounted Displays (HMDs), it is paramount that HMDs are developed that meet the operational needs of the Warfighter. During the development cycle, questions always arise concerning the operational requirements of the HMD. These include questions concerning luminance, contrast, color, resolution, and other performance parameters. When color is implemented in HMDs, which are eyes-out, see-through displays, visual perception issues become an increased concern. In particular, when HMD symbology combines with the ambient scene, the combination can produce a false perception of either or both images. Work describing the daylight luminance requirements for viable symbology has been previously published. Here we present a follow-up evaluation of possible color considerations and the effect that these choices have on perception and situational awareness. Special emphasis is placed on the evaluation of hues in CIE chromaticity space and their combination, as well as perceptual issues concerning color-deficient versus normal observers. In addition, choices are evaluated in terms of display technology and information content.