Assessing the impact unique NVG filters have on human visual performance under simulated compatible cockpit lighting

Abstract

The introduction of Night Vision Goggles (NVGs) into the cockpits of aircraft configured with head-up displays (HUDs) and colored cockpit instruments necessitated the addition of special NVG objective lens filters to ensure NVG/cockpit compatibility. Three classifications have been developed: Class A, B and C, all minus blue filters, but with different transmissivity characteristics customized to make NVGs compatible with particular cockpit configurations. Class C filters, designed for aircraft equipped with holographic HUDs, are constructed of applied reflective coatings with a built-in spectral notch for transmitting the correct light wavelength to make the projected HUD symbology readable. New absorptive glass technology was integrated into the design of an RG-665 minus-blue filter identical to a class B filter but with a physical pinhole and varying glass material thickness to fine tune the filter for optimal transmissivity for NVG/HUD compatibility. A study was conducted to examine the impact these two unique classifications of filters have on visual performance using simulated compatible cockpit lighting in a controlled laboratory. Results indicate the Class C filters significantly outperformed the RG-665 filters with the windscreen condition installed. A discussion of the properties of each type of filter and its effect on NVG visual performance are discussed in this paper.