Night Vision Compatibility Filters

Dontech’s night vision filters are primarily used in military electronic display and lighting applications. Night vision goggles (NVG) or night vision imaging systems (NVIS) must be used in an environment that will not have near infrared (NIR) noise, which would interfere with the nighttime sensitivity of the NVGs. Furthermore, night vision compatibility (NVC) is only achieved when the design of the lighting equipment allows for proper use with and without the NVIS, at night or during the day.

Dontech provides filters for use in Classes A, B and C NVIS requirements and in Type I Direct View Image NVIS and Type II Projected Image NVIS (e.g., Cats Eyes) environments. Dontech’s filters for night vision compatibility include:

  • Plastic NVIS Green A and Green B
  • Plastic NVIS Yellow
  • Plastic NVIS Red
  • Plastic NVIS White or Full Color (for white LED’s and full-color LCD’s)
  • Glass NVIS Green A and Green B
  • Glass NVIS Yellow
  • Glass NVIS White or Full Color (NIR Absorbing)
  • Glass NVIS White or Full Color (NIR Reflecting)

Night vision filters can be incorporated in front of any display or light source, or into the backlight assembly or light guides of an LCD. Full color NIR reflecting filters can only be used in the backlighting system due to photopic and off-angle reflections. Specific NVIS colored filters can be selected based on light source (LED or incandescent), transmission and NIR rejection requirements.

NIGHT VISION SYSTEMS OVERVIEW

NVIS are passive systems, typically helmet mounted binocular image intensification devices that have a very high sensitivity to radiation in the approximate region of 600nm to 930nm (orange to near infrared). The NVIS work by converting photons from the outside night scene onto a micro-displayed visible image. The NVIS will amplify the nighttime scene approximately 2000 times. To protect the image intensifier assembly, the systems are equipped with an automatic gain control (AGC) which will aperture down the NVIS when exposed to bright lights in the region of approximately 600nm to 930nm. If displays or light sources in the cockpit are not properly filtered, the AGC will activate and the NVIS will become proportionally less sensitive to nighttime objects outside of the cockpit. The NVIS are not used to read the cockpit displays (except the original AN/PVS-5), therefore the filtered displays must be visible to the unaided eye.

Avionic NVIS (ANVIS) filtering requirements are more demanding than ground based systems. To achieve NVC for a cockpit environment, there can be little to no overlap between the emissions spectrum of the display or light source and the spectral response of the NVIS. By contrast, by reducing the near IR transmittance to 5% of the total visible component will often meet the minimum necessary requirements for ground based vehicles and equipment. The filtering of commercial light sources and displays is accomplished using near infrared (NIR) absorbing glass, thermoplastic substrates which absorb NIR radiation, or thin film coatings that simultaneously reflect NIR radiation and allow visible light to pass. These filters are designed to absorb or reflect in the deep red and NIR. Often the chromaticity of the display of lighting systems must be adjusted, which can be easily accomplished along with the near IR filtering. By significantly reducing NIR radiation, night vision goggles (NVG) can be used along with electronic display and lighting systems without affecting the nighttime sensitivity of the NVIS. Secondary filtering operations such as EMI/RFI shielding, antiglare/antireflective coatings or contrast enhancement can be added to the night vision filters.

MIL-STD-3009 specifies the interface and performance requirements for aircraft lighting and display equipment that is intended to be used along with NVIS. This specification defines aircraft interior lighting standards for sources such as cockpit displays and caution / warning lights, for both day and nighttime operating conditions. NVIS filters designed for avionic applications must incorporate NIR attenuation properties, chromaticity, contrast for daylight readability and often EMI/RFI shielding. The MIL-STD-3009 superseded MIL-L-85762A on February 2, 2001. This standard also includes provisions for white light sources and for “leaky green” requirements.

Please contact Dontech to discuss your night vision optical, electrical and mechanical requirements.