The impact of changing night vision goggle spectral response on night vision imaging system lighting compatibility

Abstract

The defining document outlining night-vision imaging system (NVIS) compatible lighting, MIL-L-85762A, was written in the mid 1980's, based on what was then the state of the art in night vision and image intensification. Since that time there have been changes in the photocathode sensitivity and the minus-blue coatings applied to the objective lenses. Specifically, many aviation night-vision goggles (NVGs) in the Air Force are equipped with so-called leaky green or Class C type objective lens coatings that provide a small amount of transmission around 545 nanometers so that the displays that use a P-43 phosphor can be seen through the NVGs. However, current NVIS compatibility requirements documents have not been updated to include these changes. Documents that followed and replaced MIL-L-85762A (ASC/ENFC-96-01 and MIL-STD-3009) addressed aspects of then current NVIS technology, but did little to change the actual content or NVIS radiance requirements set forth in the original MIL-L-85762A. This paper examines the impact of spectral response changes, introduced by changes in image tube parameters and objective lens minus-blue filters, on NVIS compatibility and NVIS radiance calculations. Possible impact on NVIS lighting requirements is also discussed. In addition, arguments are presented for revisiting NVIS radiometric unit conventions.