From the work description:
XY Plotter is a machine that can move an RGB LED anywhere in a two-dimensional area. The LED position can be programmed to move precisely in a prescribed pattern, while it moves long exposure photographs are made. By documenting the moving LED, the invisible history of the light is captured. Images made with the XY Plotter record the accumulated movements of the LED. Any two dimensional vector image can be uploaded to the machine for recording.
Long exposure photographs created with the XY Plotter. All the images included here are plots of Cartwright’s track as recorded in his Latitude and Longitude Project. Different colors represent the various years of the project. These images show movements within the confines of cities Cartwright has lived. Images can be exposed with multiple years in one image or separated out year by year. Increases in luminosity show patterns formed from repeated excursions along the same track.
See more at stephencartwright.com