Visual adaptation time to ambient night light on discontinuation of Gen 2++ and Gen 3 night vision goggles use

Objectives: Night vision goggles (NVG) display brightness can disrupt visual adaptation to low ambient light levels at night. Visual acuity (VA) and contrast sensitivity (CS) are established, quantifiable indicators for assessing visual adaptation time (VAT). This study estimated and compared VAT under ambient night-time illumination conditions following the discontinuation of Generation 2++ and Generation 3 NVG use. Material and Methods: Aviator’s Night Vision Imaging System Gen 2++ and F4949 Gen 3 NVGs were used. VA and CS were measured using the USAF 1951 tri-bar resolution chart and the Pelli–Robson chart, respectively. VA and CS with Gen 2++ NVGs were assessed in 22 and 8 participants, respectively, whereas both VA and CS with Gen 3 NVGs were evaluated in 11 participants. Baseline unaided VA and CS were recorded under four ambient illumination conditions: full moon (0.1 lx), half-moon (0.05 lx), quarter moon (0.01 lx), and starlight (0.001 lx). Following 10 min of NVG display light exposure, the time required to recover baseline VA and CS under each lighting condition was measured. Results: The mean VAT for VA following Gen 2++ NVG use was 6 min 9 s, 2 min 53 s, and 1 min 41 s under quarter-moon, half-moon, and full-moon illumination conditions, respectively. The corresponding mean VAT values for CS were 3 min 36 s, 2 min 19 s, and 1 min 14 s. Among Gen 3 NVG users, the mean VAT for VA was 5 min 0 s, 4 min 43 s, 2 min 16 s, and 1 min 31 s under starlight, quarter-moon, half-moon, and full-moon conditions, respectively. The mean VAT for CS under the same illumination levels was 3 min 58 s, 2 min 52 s, 2 min 2 s, and 1 min 10 s, respectively. The findings suggest that, on post-de-goggling, lower ambient illumination has increased VAT irrespective of NVG type. Target detection may precede target recognition under quarter-moon conditions, whereas both occur almost simultaneously at higher illumination levels following removal of the Gen 2++ NVG; removal of Gen 3 NVG showed differences in target detection and target recognition times only under starlight conditions. Conclusion: The study findings provide an estimate of the time required for optimal visual identification and recognition of surrounding cues after de-goggling during NVG-assisted flight operations. The study highlights the superior performance of Gen 3 NVGs over Gen 2++ NVGs in facilitating faster visual adaptation under low-light conditions.