The effects of exposure to a 532 nm (green) laser on the visibility of flight symbology

Abstract

Visible laser light is a potential hazard to flight control because it creates glare and after-images that can interfere with the visibility of flight symbology. Two components of visibility are detection and identification (ID), but previous research has only measured the effects of laser exposures on detection. Our aims were to determine the potential of a 532nm laser to disrupt flight control by characterizing effects on detection and ID of flight symbols and if results could be fit by a glare model. Glare effects were assessed by measuring detection and ID thresholds for 6 flight symbols with and without laser illumination present. Symbols varied in size and were presented for 500ms on a dark background. The laser exposure level, 14µW/cm2, was eye-safe, but known to produce significant glare. Exposures lasted 10s and were repeated every 5s while subjects completed an adaptive threshold procedure. Glare recovery was assessed by measuring the time required for subjects to respond to the appearance of symbols when the laser was turned off. The laser glare significantly elevated detection and ID thresholds. On average, symbol brightness had to be increased from 0.3 (baseline) to 165 and 315 cd/m2 to achieve detection and ID thresholds, respectively. The degree to which detection, but not ID, thresholds were elevated was dependent on stimulus size and fit well with model predictions of contrast threshold as a function of the location of symbol outer edges (eccentricity) from the center of the glare source. Response times to the appearance of symbols after a laser exposure did not differ from baseline. Exposure to safe levels of 532nm laser radiation can cause significant glare as evidenced by the need to increase the average intensity of the flight symbols by 500X for detection. Glare had an even greater effect on ID thresholds which required symbol intensities more than 1000X baseline levels. In contrast to the glare effects, the exposure did not cause prolonged after effects.