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|  MIL-L-27160 (USAF)
d. Calculate the chromaticity coordinates of the unknown white light from the following
formulas:
RC1
X=
Y+RC +BC
1
2
Y
Y=
Y+RC +BC
1
2
The values of x and y must fall within the polygon determined in 4.5.5.2.1
4.5.5.4 Brightness. Brightness measurements shall be made as follows:
a. Apply 4.50 0.050V
b. Use the specified calibration procedures
c. Turn the filter wheel to the Y (foot-lambert) position and record brightness directly.
Brightness measurements shall be taken of the lighted portion of the indicator. Readings
shall fall within the limits required in 3.3.5. Readings of one particular area, such as an
indicia, mark, or number, shall be the average of that area. the average of an areas is the
arithmetic average of a minimum of three measurements in the area. The magnitude of the
actual readings that make up the average shall not exceed a 3 to 1 variation which shall be
calculated by dividing the minimum brightness reading in a particular area into the
maximum reading in that area. For large areas, such as pointers, several subareas shall be
read and reported separately (hub, center, and tip) where each reading is the average of
serveral measurements in that subarea.
4.5.5.5 Stray light. The brightness of any point on a sheet of white paper conforming in
shape to the outer edge of, and perpendicular to, the coverglass of round instruments shall
not exceed 0.20 foot-lambert. Where the instrument bezel is other than round, a sheet of
white paper shall be placed perpendicular to the coverglass and on any line parallel to the
top edge of the coverglass. The brightness of any point looking down on the paper shall
not exceed 1.50 foot-lamberts and of any point looking up on the paper shall no exceed
0.20 foot-lambert. The sheet of white paper used in the above measurements shall be
neutral, diffusing, and shall have a reflectance of 85 5 percent. All measurements shall be
made at 4.5 0.050V excitation and 0.5 inch in front of the coverglass.
4.5.6 Contrast. The illumination for the contrast measurements shall be furnished by
uniform, diffused, artificial illumination. Contrast measurements shall be taken with no
coverglass or other transparent surface in front of the presentation. Several brightness
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