Development of Infrared Specifications for Night Vision Goggle-Compatible Light-
Emitting Diode L-810 and L-864 Obstruction Light Fixtures

After extensive use by military aviators, night vision goggles (NVG) are now increasingly utilized by civilian pilots to conduct search-and-rescue, emergency medical transport, and other flight operations.  However, with the use of light-emitting diodes (LED) in place of incandescent fixtures for obstruction lighting, the Federal Aviation Administration (FAA) has found that some pilots using NVGs are unable to see red LED obstruction lights because the light generated falls outside the visible spectrum of certain classes of NVG lens filters.

Researchers from ATR, Rensselaer Polytechnic Institute, and CSRA Inc. conducted this research effort in three phases.  Phase 1 consisted of a literature review to determine suitable IR wavelength and minimum vertical beam spread specifications.  Phase 2 consisted of conducting laboratory testing of commercially available incandescent and LEDs with IR L-810 and L-864 fixtures.  Phase 3 consisted of conducting flight evaluations to determine the minimum level of radiant intensity needed for pilots to acquire the obstruction lights.

Based on the research conducted, the following specifications are recommended for the L-810 and L-864 fixtures: 

1. L-810:  A nominal IR output wavelength of 800-900 nanometers (nm); a minimum vertical beam spread of 10° with a center between +4° and +20° at all radials throughout 360° (same as the FAA requirements for visible light); and a minimum IR radiant intensity of 4 milliwatt per steradian (mW/sr).
2. L-864:  A nominal IR output wavelength of 800-900 nm; a minimum vertical beam spread of 3° at all radials throughout 360° (same as the FAA requirements for visible light); and a minimum IR radiant intensity of 246 mW/sr.

Authers: Canter, Garrison; Freyssinier, Jean Paul; DiPilato, Michael; Gallagher, Donald