Abstract: A light pen for converting a conventional graphics plotter into a photoplotter includes a housing containing an electrically powered light source, a battery and a normally open switch. The housing has an aperture opposite the light source. The light pen replaces an ink pen in the plotter. When the light pen is urged against a photosensitive sheet in the plotter, the normally open switch is closed, the light pen is energized and the light pen is transmitted to the sheet to illuminate it. The self-contained light pen is free of trailing electrical and optical cables that might interfere with plotter speed and accuracy.