1. In an electronic control system for controlling automotive vehicle vision related equipment, said vision related equipment including a rearview mirror comprising an electrochromic variable reflectance member the reflectivity of which varies as a function of electrical signal levels applied thereto, said system including microcontroller means, ambient light sensing means effective to sense ambient light and generate a corresponding analog electrical signal indicative of the ambient light level, glare sensing means effective to sense glare causing light and generate a corresponding analog electrical signal indicative of the glare causing light level, means digitizing each of the analog signals and converting each of the digitized analog signals to a corresponding logarithmic signal representation which is accessible to said microcontroller means, means for supplying electrical power to said system, and means electrically connected to said microcontroller means and operable to apply an electrical control signal to said electrochromic variable reflectance member to change the reflectance thereof as a function of the logarithmic signal of the sensed ambient light level and the logarithmic signal of the sensed glare causing light level.