Abstract: A computer controlled photoplotter includes a row of LED's mounted to a light head positioned parallel to the film width. The light head is part of a light head assembly which is moved parallel to the film length. At the end of each pass the light head is indexed widthwise a short distance. During each lengthwise pass the LED's are illuminated at appropriate positions to expose the film at those positions according to the image being plotted. To equalize the illumination intensity of the LED's, the output of each LED is measured and the value is combined with a standard value. The result determining how long the LED is turned off during an intermediate segment of the actuation signal.