An Assessment of Luminance Imbalance with ANVIS at an Army Helicopter Training Airfield.

One of the casual factors listed in a 1996 mid-air collision between two Australian Army helicopters in formation was a speculation of possible luminance imbalance between the right and left channels of the night vision goggles NVGs at the airfield of origin for the two helicopters involved in the accident. This study describes a field method of measuring and determining luminance output and imbalance for 20 pair of NVGs at a U.S. Army airfield. The luminance source to activate the aviator night vision imaging system ANVIS was a calibrated NVG test set TS-3895 UV. The photopic sensor of an illuminance radiometer was placed on the eyepieces of the ANVIS and relative illuminance values were taken for each channel at light levels above and below the automatic brightness control ABC level in the ANVIS power supply. The light level above the ABC limits the upper luminance output and the level below the ABC is a function of the ANVIS gain. In the laboratory, the illuminance values from the radiometer were calibrated to luminance values using the same NVG test set for the light source and a Pritchard 1980A photometer. The results showed a significant correlation between the luminance values from the right and left eyepieces above or below the ABC level, but the correlation below levels for the same tube was not significant. It was also found that 80 percent of the surveyed ANVIS that had been routinely used for several years did not meet the suggested 10 percent luminance imbalance criteria for either above or below the ABC level. The implication from this study is that the 10 percent imbalance criteria is not realistic from a measuring or user acceptable standpoint.