A wireless sensor for measuring a light intensity comprises a photosensitive circuit that can be disabled, for example, to conserve battery power. The wireless sensor may further comprise a wireless transmitter for transmitting wireless signals, a controller and a battery for powering the photosensitive circuit, the wireless transmitter, and the controller. The photosensitive circuit may generate a light intensity control signal in response to the light intensity. The photosensitive circuit may include a photosensitive diode for conducting a current having a magnitude responsive to the light intensity. The controller may be configured to disable the photosensitive circuit by opening a controllable switch that is coupled in series with the photosensitive diode. The controller may enable the photosensitive circuit, subsequently sample the light intensity control signal at a sampling period, and then disable the photosensitive circuit after the light intensity control signal has been sampled.