Scratch and Dig
Although this standard is based on a comparison to a certified optical comparator, the following general guideline is commonly accepted when referencing a scratch and dig specification: The first number represents the maximum allowable scratch width in microns (20/10 = no scratches greater than 20um wide allowed). The second number represents the maximum allowable dig in 10's of microns as measured LxW/2 (20/10 = no digs greater than 100um allowed).
120/80
Defects are clearly visible in normal room lighting. This is generally a commercial specification for glass that will be exposed to further wear.
60/40
Defects are visible under fluorescent lighting (1.5K Lux). Common for non-magnified optical applications.
20/10
Defects require hi-intensity halogen lighting to identify (10K Lux). Specified for critical optical applications.
80/50
Defects are discrete but visible in normal room lighting. Typical for commercial and noncritical optical applications.
40/20
Defects are difficult to detect under fluorescent light and may require a low-intensity halogen lamp (5K Lux). Typical optical applications.
10/5
Defects require hi-intensity halogen lighting to identify (15K Lux or greater). Specified for the most critical optical applications.