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Step 2
Evaluate the display luminance. Luminance (L) is the area under the curve obtained by multiplying the display radiance (figure 11a) and the photopic response (figure 11d). The resultant curve is shown in figure 11e.
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| Figure 11d: Photopic response curve. |
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Figure 11e: Product of display spectral radiance and photopic response curve (luminance). |
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Although not separately defined by MIL-L-85762A, the overlap radiance (R) is a useful quantity for simplifying the calculation of NR:
where the constant 0.1 is the normalizing luminance level for green, and 15 for yellow and red, as specified in MIL-L-85762A.
MIL-L-85762A sets minimum and maximum limits for NR. Because yellow (caution) and red (warning) displays must attract pilot attention in both daylight and NVIS missions, MIL-L-85762A sets minimum NR levels for yellow and red high enough to attract the pilot's immediate attention.
Because there are two NVIS response curves, Class A and B, there are two corresponding classes of NR: NRA and NRB. For information on measurement methods, see Measuring and certifying NVIS compatibility.
When Korry produces an NVIS-compatible indicator, switch, switch panel or keyboard, the filter assembly is a critical part of the product, because more than any other single component it ensures NVIS- compatible illumination. Korry's proprietary NVIS filters are designed to meet the NR limits of MIL-L-85762A by safety factors of 1.5 to more than five, depending on the color and the light source. We offer filters suited for incandescent, EL, or LED light sources. In addition, we design the mechanical packaging of every NVIS-compatible product specifically to prevent unfiltered light leaks. The best filter in the world will not meet NR specifications if the mechanical seal permits any light leaks.
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