MILDTL28803C
4.6.2 Operating characteristics (see 3.5.2). Displays shall be measured for operating characteristics in
4.6.2.1 Character distortion (see 3.5.2.1). The lighted character(s) shall be visually examined for uniformity of
character brightness, legibility, and clearness of display. The light character(s) shall be visually examined while being
viewed at a distance of 18 inches (457 mm) in a plane normal to the lens face to determine distortion (see 3.1).
4.6.2.2 Dot-to-dot ratio (see 3.5.2.2). Using the luminance values recorded during the luminance test (see 4.6.16),
the dot-to-dot ratio (D) shall be determined by using the highest recorded point reading and the lowest recorded point
reading and calculation:
highest recorded point reading
D =
lowest recorded point reading
4.6.3 Optical characteristic tests.
4.6.3.1 Chromaticity (see 3.5.3.1). The chromaticity shall be determined by spectrographic means as specified
a.
Method I. Spectrophotometer flat slab: Chromaticity shall be determined using a spectrophotometer, flat
slab material of the same density and thickness of the shaped filter, and necessary calibration filters.
b.
Method II. Spectroradiometric: Chromaticity shall be determined using a spectroradiometer, a complete
illuminated display assembly, calibrated lamps of specified color temperature, and necessary calibration
filters.
c.
Method III. Visual comparator: Chromaticity shall be determined by a color comparator, necessary high and
low limit plastic or glass filters of known chromaticity, and calibrated light sources of specific color
temperature.
4.6.3.2 Contrast ratio (see 3.5.3.2). Displays shall be tested, when specified, in accordance with 4.6.3.2.1 and
4.6.3.2.2. A light source with a color temperature between 3,000 and 5,000 degrees Kelvin shall be directed from an
angle of 45 degrees ±2 degrees to the normal of a diffuse white reflectance standard (pressed from barium sulfate
or Polytetrafluoroethylene resin powder). The size of the of the light source shall be limited to a conical full angle ≤
20 degrees as measured from the center of the reflectance standard. The photometer shall be placed at 90 degrees
to and focused on the center of the reflectance standard. The light source shall be adjusted to produce a reading of
6,568 foot-lamberts (22503 candela per square meter) (equivalent to an incident illumination of 9,290 foot-candles).
The reflectance standard shall be removed and replaced with the display to be tested. The viewing surface of the
display shall be placed in the same plane as at the reflectance standard and moved as required to make the specified
measurements. The relative positions of the light source and the photometer shall not be changed during these tests.
4.6.3.2.1 Contrast ratio with all segments illuminated. At least two readings shall be taken at equidistant points on
each illuminated segment. The readings shall be averaged. At least two readings shall then be taken at equidistant
points in the background immediately next to each illuminated segment. The background readings shall also be
averaged. The contrast ratio shall be determined by measuring B1 (average brightness of background) and B2
(average brightness of segment) and calculating:
B2 B1
C =
B1
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