Patent ID: 7505136

Claim:
A system comprising: a light source configured to emit a beam of known intensity at a dimmable element of an electrically dimmable window system; a light intensity sensor configured to measure a measured light intensity of light passing through the dimmable element, and to output a first signal indicative of the measured light intensity; an input configured to receive a second signal, wherein the second signal indicates the known intensity and a desired transmissivity of the dimmable element; and a controller configured to: calculate an actual transmissivity of the dimmable element from the known intensity of the light source and the measured light intensity; compare the actual transmissivity to the desired transmissivity to generate a comparison; and generate a third signal indicative of the comparison, wherein the controller is in communication with a control system of the electrically dimmable window system, and wherein the actual transmissivity of the dimmable element can be adjusted based on the intensity measured by the sensor.