Controlling transitions in optically switchable devices

A controller for controlling a change in optical state in a switchable optical device, the controller comprising:

• (a) one or more interfaces for providing control instructions, a driving voltage, and/or a driving current to the switchable optical device;
• and
• (b) instructions for controlling the change in optical state, wherein the instructions comprise:
• (i) controlling the current to the switchable optical device during an initial portion of a transition from a first optical state to a second optical state, wherein controlling the current is accomplished by correcting the current to the switchable optical device when the magnitude of the current exceeds an upper defined safe current level or fails to meet a lower defined fast switch current level;
• and
• (ii) controlling the voltage applied to the switchable optical device during a later portion of the transition from the first optical state to the second optical state such that the magnitude of the voltage is held substantially at a preset level.