An optical radiation sensor system having: a housing having a distal portion for receiving radiation from the radiation source and a proximal portion; a sensor element in communication with the proximal portion, the sensor element configured to detect and respond to incident radiation received from the radiation source; and motive structure configured to move the housing with respect to the sensor element between at least a first position and a second position. A radiation pathway is defined between the radiation source and the sensor element when the housing is in at least one of the first position and the second position. Movement of the housing with respect to the sensor element causes a modification of intensity of radiation impinging on the sensor element.