Helmet-Mounted Displays: - USAARL - The - U.S. Army

Optical Performance 167
C m = (L max - L min ) / (L max + L min) (Modulation contrast) Equation 5.3a
and
= | (L t - L b )| / (L t + L b) | Equation 5.3b
For the values above,
Contrast ratio
C m
= | (L t - L b )| / (L t + L b) |
= (884 - 750) / (884 + 750)
= 134 / 1634
= 0.08 for the clear visor,
= (293 - 159) / (293 + 159)
= 134 / 452
= 0.3 for the shaded visor.
Contrast ratio is defined as follows
C r = L t / L b for L t > L b (Contrast ratio) Equation 5.2a
= L max / L min
For the values above,
Shades of grey
C r
= 884/750
= 1.17 for the clear visor, and
= 293/159
= 1.84 for the shaded visor.
Number of shades of grey is defined as follows:
Equation 5.2c