MIL-PRF-38169A
4.4.5 Optical distortion. To determine optical distortion in the critical areas, the visor or goggle
lens shall be inserted with its surface normal to the line of sight into a distortion test apparatus, an
example of which is described in figure 3. The observed distortion patterns shall be equal to or
more parallel than pattern numbers 1-5 in figure 4.
4.4.6 Haze. The haze value shall be determined in accordance with an acceptable commercial
process such as that contained in ASTM D 1003 and shall be 5% or smaller.
4.4.7 Extended electromagnetic radiation transmittance of class 3 visor and goggle lens. The
extended electromagnetic radiation transmittance of the class 3 visor and goggle lens shall be
measured with an automatic recording spectrophotometer. The average for each range shall be
calculated separately, taken every 10 nm. The monochromator of this spectrophotometer shall
vary continuously from 200 to 2500 nm. The recording sheet for each visor and goggle lens
tested shall show a base line and the two smooth curves, one for each point C. Transmittance
shall be measured at points C for the left and the right eyes by examination of the transmission
curves and by calculating the averages.
4.4.8 Erythemal ultraviolet transmittance of class 1 and class 2 visor and goggle lens. Erythemal
ultraviolet transmittance shall be measured by a spectrophotometer, and shall be less than 5%
when computed as the average spectral transmittance at wave lengths of 250, 270, 290, 300, 310,
and 320 nm.
4.4.9 Neutrality. The spectral transmittance (380-770 nm) of the class 2 visor and goggle lenses
shall be measured by a spectrophotometer having a monochromator band width of 10 nm or less
and a reproduction of ± 1%. The neutrality shall be calculated by the Judd Daylight Duplication
Method (see 6.3.3), or equivalent.
4.4.10 Spectral transmittance. The spectral transmittance of class 1 and 2 visor and goggle lenses
shall be determined with an automatic recording spectrophotometer or equal (see 6.3.3).
4.4.11 Chromaticity of class 2 visor and goggle lens. The chromaticity coordinates x and y shall
be calculated from spectrophotometric data. Table II illustrates a method of such calculations
(see 6.3.4).
4.4.12 Colorfastness to light of class 3 visor and goggle lens. The colorfastness test shall be
conducted using the appropriate portions of ASTM G 23 or an equivalent commercial testing
procedure. Each side of the visor and goggle lens shall be subjected to the test procedures. After
this test, the average spectral transmittance of the visor and goggle lens in the range between 380
and 770 nm shall be 2% (± 0.5%).
4.4.13 Resistance to thermal shock of class 3 visor and goggle lens. The visor and goggle lenses
shall be exposed in air to temperature extremes alternately for 10 cycles. Each cycle shall consist
of exposure to 40±5 °F, followed immediately by exposure to 160±5 °F. The length of time in
minutes of exposure to each temperature is determined by multiplying the thickness in inches of
the visor and goggle lens by 400. After completion of the 10 temperature cycles, the average
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