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Filtering LEDs
Selecting the correct LED and NVIS-filter combination is an important aspect of display design.
Read background information on LED light sources in night-vision applications.
 Nightshield filter specifications for LED applications
Broadband versus narrow-band LED
The LEDs in a display heavily influence its color, contrast, and NVIS radiance (NR) properties. White LEDs with broadband spectral emission can be filtered with Nightshield to produce displays that comply with various NVIS color coordinates described in MIL-STD-3009. On the other hand, monochrome narrow-band emission LEDs with non-compliant color coordinates generally cannot be rendered compliant with the addition of an NVIS filter.
If a specific color coordinate range is critical to a design, it is important to select either:
- A broadband LED source that can be filtered to the correct color coordinates, or
- A narrow-band LED source that inherently complies with the correct color coordinates.
NVIS Green A and B for primary and secondary lighting components
MIL-STD-3009 describes the color coordinates and NVIS radiance required for various NVIS compatible lighting components (see Table II, III, and IIIa in MIL-STD-3009 for a summary of color and NVIS radiance requirements). Paragraphs 4.3.4.1 through 4.3.4.6 describe applications requiring NVIS Green A and NVIS Green B color values. Primary and secondary lighting components typically require NVIS Green A or Green B color properties (hence paragraphs 4.3.4.1 through 4.3.4.6 may be used as reference for primary and secondary lighting components). These lighting components must be NVIS compatible when the luminance is scaled to 0.1 fL.
NVIS Yellow and Red for Master Caution and Warning illumination
Master Caution Advisory Lighting components are described by paragraphs 4.3.4.7 and 4.3.4.8 and must comply with NVIS Yellow color values. Similarly, Warning Signals are described in paragraph 4.3.4.8 and must comply with NVIS Red. Master Caution and Warning Signals must be NVIS compatible when the luminance is scaled to 15 fL.
Segmented, dot-matrix, and backlit displays
Segmented and dot-matrix LED displays are not bound by any specific color coordinates, but must be NVIS compatible when scaled to 0.1 fL (see MIL-STD-3009, Appendix C, Para 6.2). Similarly, displays backlit with monochrome or white LEDs and requiring at least eight shades of gray are not bound by any specific color coordinates, but must be NVIS compatible when scaled to 0.5 fL (see MIL-STD-3009, Para. 4.3.5.9.1).
Short-lead engineered sheet material for machining LED ring filters
As an alternative to molded LED ring filters, typically with long lead times, Korry offers Nightshield engineered sheets, delivered with a short lead time.
NVIS compatibility is achieved when the ring filter is machined with a wall thickness of 0.028” ± 0.002”. These sheets are available for NVIS Green A and NVIS Green B applications when using white or green LEDs. The sheets are manufactured to a minimum thickness of 0.2”. Hundreds of ring filters can be machined from each sheet. The actual number of ring filters per sheet depends on the filter design as well as the machining kerf.
Guidelines for cutting and milling Nightshield plastic material
If you require a polished surface, Korry recommends either laser cutting or coating the milled filter with clear overcoat paint. Other colors and thicknesses are available on a custom basis. An export license may be required for international applications.
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