A color's Light Reflectance Value (LRV) measures the amount of visible and usable light that reflects from (or absorbs into) a surface. Simply put, LRV measures the percentage of light a color reflects. Forming a universal value for contrast expressed on a scale of 1 - 100, with 1 equalling absolute black and 100 equalling absolute white. The higher the value obtained, the greater the amount of light that is being reflected.
The European Equality Act 2010 is a European law which requires a 30 point difference between floors and walls to assist in the safety of people with disabilities. The typical optimal choice for everyday design considerations are LRV's between 9 and 75.