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 .