Night Vision Goggles (NVGs) and Obstruction Lighting Using Light Emitting Diode (LED) Sources - Service Difficulty Alert

AL 2009-02
20 April 2009

Purpose: This SA advises operators that certain LED light units may not be seen through NVGs.

Discussion: A Flight Safety Flash was issued in 2008 by the Canadian Air Force’s Directorate of Flight Safety, which identified some red obstruction lighting systems that were clearly visible to the naked eye but not visible with NVGs.  These lighting systems employ LEDs instead of traditional incandescent sources.  The use of LEDs is becoming more common because of their energy efficiency and long life. 

Only a minute portion of the radiation spectrum is available for human vision and ranges from about 400 to 700 nanometers (nm).  Aviation Red lights have an output from about 610 to 700nm.  NVGs approved for civil aviation (having a Class B Minus Blue Filter) are sensitive to energy ranging from 665 to about 930nm in the infrared region. Because LEDs have a relatively narrow emission band and do not emit infrared energy [heat] like incandescent lights, it is possible for them to meet Transport Canada requirements for Aviation Red yet may not be observable through NVGs.

In brief, NVG users should be aware that LED lighting systems falling outside the sensitivity range of an NVG may not be seen.  Crews that fly using NVGs are warned to use extra caution when flying near obstacle areas and to report any hazardous sites to the nearest flight service station.

Recommended Action: Pilots, directors of operations, chief pilots, training program managers, and training centers either using, or providing training for NVGs should advise pilots of the limitations outlined in this SA and ensure such information is incorporated into the pilot NVG training program.

Queries/Information:  For further information contact a Transport Canada Centre, or call Mr. Bob Grant, Inspector, AIS & Airspace Standards - AARTAC, telephone 613-990-5443 or email

D. Sherritt
Director, Standards

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