The increased reliance on night operations by the military over the last few decades has led to the development of various night imaging devices. Night vision goggles (NVGs) are one device which have gained widespread use in nighttime helicopter operations. However, rotorcraft accident data have indicated an increased occurrence of "pilot error" type accidents when NVGs are in use. NVG related accidents often can be linked to extremely poor ambient lighting and contrast conditions during nighttime operations as well as the imaging limitations of the NVGs. Research has shown that NVGs reduce visual acuity and depth perception when compared to unaided daylight viewing conditions.

In this study the effects of illumination and contrast on stereoscopic vision with and without AN/AVS-6 goggles were investigated. Stereoacuity was measured using a modified Howard-Dolman apparatus with four levels of illumination and three levels of contrast. Testing was performed with NVGs for nighttime illuminations and unaided for daytime levels of illumination. Image measurements were performed on the NVGs to determine the impact of illumination on resolution and signal-to-noise ratio.

Stereoscopic vision with NVGs was found to be significantly worse than under daylight conditions. Low levels of contrast also were found to reduce stereoacuity significantly. It was found that the worst stereoacuity in this study occurred under half moon or higher illumination levels. This research revealed that further NVG development should focus on the limitations of the NVGs under high light levels, and special considerations should be made for using NVGs in low contrast, high luminance situations.