A new night vision goggles (NVG) gain definition for the calibration process is proposed and evaluated. This definition is based on the radiance measurements at the input and output of the NVG. In contrast to the old definition which uses a non- International System of Units (SI) traceable luminance, equivalent luminance unit, the new definition utilizes the radiance quantities that are traceable to the SI units through NIST standards. Due to the implementation of the scaling coefficients originating from the NVG spectral responsivities, the same NVG gain is expected within both definitions. The new definition was evaluated at the NIST night vision calibration facility and the experimental data were compared to results obtained with a commercial test set (CTS). The comparison of the radiometric quantities indicated differences up to 15 % originating from the available CTS. However, at proper calibration, an equal NVG gain within both new and old gain definitions was measured for the 4th generation goggle. The NVG gain uncertainty analysis including the effect of the no-moon night sky radiation was performed for goggle type A, B, and C.
night vision goggle (NVG), NVG gain, NVG radiometric quantities, night sky