The spaces between each letter in a word. Light Reflectance Value A relative term used to describe how well a surface reflects light. Contrast is calculated in percent between foreground and background, e.g. light color on dark background. The standard for readability is a contrast of at least 70%. The readability is determined by the formula: Contrast=[(B1-B2)/B1] x 100 where B1= light reflectance value (LRV) of the lighter area and B2= light reflectance value of the darker area.