MIL-L-85762 and MIL-L-85762A
(currently MIL-STD-3009)
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MIL-L-85762A classifies Gen 3 NVIS-compatible lighting according to NVIS type and class:
Type I Direct View Image
The view through the goggle eyepiece includes only the NVIS phosphor-screen image. The pilot must glance down to see his instruments. This is used primarily in helicopters.
Type II Projected Image
Addition of a combiner lens to the eyepiece allows the pilot to simultaneously view the NVIS phosphor-screen image and crewstation instrumentation. This is used primarily in fixed-wing aircraft, and is a real advantage in low-flying jets. Combiner lenses also provide improved compatibility with head-up displays.
Class A
Addition of a 625 nm minus-blue cut-on filter to the objective lens produces the response function shown in figure 8. The one-percent relative response is at 595 nm, which allows crewstation illumination in blue, green (advisory) and yellow (caution, master caution, warning). To avoid interference from orange and red displays, MIL-L-85762A excludes them from Class A crewstations. Class A is used primarily in helicopters.
Class B
Addition of a 665 nm minus-blue cut-on filter to the objective lens produces the response function shown in figure 8. Here, the one-percent relative response is at 625 nm, which excludes most of the red from the NVIS response to allow crewstation illumination in blue, green (advisory), yellow (caution), and red (master caution, warning). Class B is used in fixed-wing aircraft.
This scheme defines four categories of NVIS, of which only two are widely used (Type I, Class A and Type II, Class B). Type I, Class A is the same as the older designation ANVIS.
Figure 10: MIL-L-85762A NVIS classification. Type I, Class B and Type II, Class A are not typically used.
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