Electrochromic device capable of prolonged coloration

An electrochromic mirror system for a vehicle comprising:

• an electrochromic reflective device having a continuously variable reflectance characteristic;
• said reflective device being responsive to a momentary application of a signal having a given value by coloring to a given partial reflectance level and responsive to removal of said signal by maintaining a reflectance level that is within a given percentage from said given reflectance level for a given period of time defining a memory time constant for said reflective device;
• said partial reflectance level being selectable from a continuum of light reflectance levels from a highest light reflectance level to a lowest light reflectance level;
• input means for selecting a reflectance level of said reflective device;
• circuit means responsive to said input means for applying to said reflective device a value of said signal corresponding to the selected reflectance level, said circuit means applying said selected signal value for a first predetermined period of time in order to color said reflective device to said selected reflectance level and repetitively thereafter for second predetermined periods of time in order to maintain said selected reflectivity level, said second period being separated from said first period and from each other by holding periods of time during which said selected signal is not applied to said reflective device, the duration of said holding periods being a function of said memory time constant;
• sensing means for providing an indication that said input means has selected a different light reflectance level;
• and
• said circuit means being responsive to said indication by changing out of a holding period if in such holding period to a period of time that is not a holding period to thereby apply to said electrochromic reflective device a changed value of said signal.

A variable electrochromic light transmission system comprising:

• an electrochromic element having a continuously variable transmission characteristic, said electrochromic element being one of a rearview mirror and a glazing element;
• said element being responsive to a momentary application of a signal by coloring to a partial light transmission level and being responsive to removal of said signal by maintaining a transmission level that is within a given percentage from said partial transmission level;
• said partial light transmission level selectable from a continuum of light transmission levels in a range from a highest light transmission level to a lowest light transmission level;
• input means for selecting a light transmission level of said electrochromic element;
• and
• circuit means responsive to said input means for intermittently applying a drive signal to said electrochromic element in successive pulses separated by holding periods in order to color said electrochromic element to a particular light transmission level;
• said drive signal having a given polarity and a level corresponding to the selected transmission level;
• and
• said circuit means being responsive to at least one of the magnitude and the rate of change of magnitude of said input means to change out of a holding period if in such holding period to a period of time that is not a holding period and to momentarily apply an undervoltage level of said drive signal of said given polarity representing a light transmission level that is higher than the selected level when said input means selects an increased light transmission level and to momentarily apply an overvoltage level of said drive signal of said given polarity representing a light transmission level that is lower than the selected level when said input means selects a decreased light transmission level.