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).
Defects are clearly visible in normal room lighting. This is generally a commercial specification for glass that will be exposed to further wear.
Defects are visible under fluorescent lighting (1.5K Lux). Common for non-magnified optical applications.
Defects require hi-intensity halogen lighting to identify (10K Lux). Specified for critical optical applications.
Defects are discrete but visible in normal room lighting. Typical for commercial and noncritical optical applications.
Defects are difficult to detect under fluorescent light and may require a low-intensity halogen lamp (5K Lux). Typical optical applications.
Defects require hi-intensity halogen lighting to identify (15K Lux or greater). Specified for the most critical optical applications.