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

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Clarence E. Rash and William E. McLean
Figure 5.1. Luminance patterns for several combinations of target
and background luminance values.
Assume, now, that the target luminance becomes significantly larger,
5000 fL for example, but with the same background value (Figure 5.1b).
The contrast value using Equations 5.1a and 5.1c would be:
C = (5000 - 20) / 20 = 249
The contrast ratio using Equations 5.2a or 5.2c take the value:
C r = 5000/20 = 250
Further increases in the value of the target luminance would continue
to produce larger values for contrast as defined by Equations 5.1a and 5.1c
and contrast ratio as defined by Equations 5.2a and 5.2c. Note that as L max
(or L t ) becomes significantly greater than L min (or L b), the contrast values
of Equation 5.1a and 5.1c approach the contrast ratio values of Equations
5.2a and 5.2c. This can easily be seen by rearranging Equation 5.1a into
the following form:
C = (L t / L b ) - 1 Equation 5.8