The contrast ratio of the display screen should be a minimum of 6:1; a contrast ratio of 10:1 is preferred. Additional Information: Modern visual display devices can have considerably higher stated contrast ratio capability than 10:1, but glare and reflections can substantially reduce the actual contrast ratio of the screen. This contrast ratio should include any contributions caused by ambient light, reflections, or glare on the display screen. Either display polarity (i.e., dark characters on a light background or light characters on a dark background) is acceptable, provided it meets the guidance for display screen resolution (above) and screen luminance. When ambient illumination near the display screen is high (greater than or 540 lx, or 50.2 fc), dark characters on a light background should be used. The contrast ratio (CR) is calculated as follows:
CR = Lmax / Lmin,
where Lmax is the higher luminance of the background or of the character, and Lmin is the lower luminance of the two. These values include the contribution from ambient light. Small characters
(i.e., characters between 10 and 17 minutes of arc) should have a minimum luminance modulation (M) of:
M = 0.3 + 0.07 (20 -S),
where S is the vertical size of the character set, in minutes of arc, and Luminance modulation is calculated M = (Lmax-Lmin)/(Lmax + Lmin). See IDMS (2012) for measurement information. 5908, 0700, 1472G, 100