An exposure system for light sensitive materials held in a vacuum frame includes an electrical light source and a power supply to the light source, the power supply having a power consumption monitor so it can modify the power supplied to the light source to compensate for any fluctuations in power consumption by the light.The light source is supported in a housing having air exhaust openings proximate the mid-portion of the light source. A blower cools the light source with a helical airflow. The voltage drop across the electrical light source is used to control the speed of the blower to maintain the voltage of the light source at a desired level. The housing has an open face and a removable pane. An indicator indicates the presence of the pane. A metal shutter in the housing has a black ceramic surface adjacent the light source to selectively expose light sensitive materials. A control means closes the shutter when the indicator senses removal of the pane while power is being supplied to the light source. The control means includes a timer to hold the shutter closed for a period of time after the switch is opened, long enough to permit cooling of the light source and opens the shutter after expiration of the period. It also actuates the blower during the period to hasten the cooling of the light source.The control unit to control operating parameters of a plurality of subsystem units of the exposure system includes an electronic memory unit and means responsive to signals stored in the electronic memory unit to control variables. The control lines of the control unit and the subsystem units have a plurality of physically equivalent, but electrically unique, pin socket outputs each having a plurality of electrical leads. A plurality of cables having physically and electrically identical terminations are provided, so that any of the cables may be used to connect a pin socket of the control unit to a pin socket of a subsystem unit.The control unit includes a keyboard input to the memory storage means of variables to be stored. The keyboard includes function keys to select the variable to be assigned a value and numeric keys to assign a numeric value to a selected numeric variable.