Visual acuity is the ability of the human eye to discriminate between adjacent objects. It depends to a significant degree on the levels of contrast and luminance in the field of vision. Optimum conditions start at around 100 cd/m2 with a contrast difference of over 90%. At average reflectance this corresponds to an illuminance of 1000 lx. In the case of moving objects visual acuity increases slightly, reaching a maximum at angular velocities of 2-3 degrees of angle per second.