Experimental Evaluation of Head-Up Display High Brightness Requirements

Abstract

The experimental design was originated by Kelley and Strudwick for V/HUD prototype equipment utilization. Their plan was modified at Kaiser by Ketchel and R. W. Way who designed and constructed the symbol generating apparatus described herein.Experiments were conducted at the Kaiser Palo Alto facility by the authors. Subjects were selected Kaiser personnel with the exception of Mr. Strudwick who served alternately as subject and experimenter.ii ABSTRACT The HUD, or Head-up part of Kaiser's Vertical/Head-up Display, is an avionics device that collimates and projects symbology onto the real world at infinity. It enables a pilot to look through the aircraft windscreen while viewing command and status information without requiring visual accommodation changes.This experiment was undertaken to determine what symbol brightness is required to use the Head-up Display under high background brightness conditions. The anticipated worst situation (other than looking directly into the sun) consists of flight over sunlit clouds or snow, in which case there could be continuing background brightnesses on the order of 10, 000 foot lamberts against which the display must be seen.Results indicate that pilots will want display contrasts of at least 20 to 35 per cent, i. e. , perhaps 1800 to 3500 ft. L. display brightness reflecting from the HUD combining glass, assuming 90 per cent transmission by windscreen and combining glass and an external background luminance of 10, 000 ft. L. The minimum brightness contrast for a barely visible, near-threshold display is on the order of 10 per cent, or 900 to 1, 000 ft. L. reflected from the combiner.This will provide an extremely dim display, but one that most pilots can be expected to see more than 90 per cent of the time.iii

Human factors engineering for head-up displays: A review of military specifications and recommendations for research.

“…The result is that a less powerful light source is needed to achieve acceptable symbol to background contrast, while outside viewing remains at an acceptable level. Kelley et al (1965) studied several different combining glasses with a constant 10,000 foot-lambert background to determine contrast thresholds. Subjects had to identify orientations of a horizon line and angle of attack indicator representing a coarse and a fine discrimination respectively.…”

“…In short, the study of Human Factors for trichroic filters on HUDs has not reached an advanced level. On the other hand, the results of Kelley et al (1965) together with the advantages of less power required by the light source suggest that trichroic filters ought to be studied in depth. Other filter types and filter combinations ought to be tested also (see Semple et al, 1971).…”

“…Under these conditions, estimates of acceptable contrast ratios range from about 5 to 30 percent of the light transmitted through the combining glass. The 5 percent figure is from the Kelley et al (1965) study using the 90 percent accuracy threshold with a trichroic color-coated combiner. The 80 percent contrast figure has been taken by Opittek (1973) as a design goal for comfortable vision.…”

Effects of luminance contrast and font size on dual‐plane head‐up display legibility (“The Double 007 Rule for HUDs”)

“…Weintraub (1992) reviewed a study in aircraft cockpit that suggested a minimum luminance contrast at 1.15:1 and a preferred luminance contrast at 1.5:1 under moderate ambient illumination and higher luminance contrast such as 4:1 in low ambient illumination. 1,2 A HUD study performed by Kelley et al (1965) showed that subjects could read alphanumeric symbols comfortably with luminance contrast levels above 1.4:1. 3 A helmet-mounted display study conducted by Cohen et al (1979) found that luminance contrast less than 1.23:1 was not acceptable.…”

“…1,2 A HUD study performed by Kelley et al (1965) showed that subjects could read alphanumeric symbols comfortably with luminance contrast levels above 1.4:1. 3 A helmet-mounted display study conducted by Cohen et al (1979) found that luminance contrast less than 1.23:1 was not acceptable. 4 The size of alphanumeric symbols is another factor which affects the legibility of the HUD.…”