The video below features a stela found in the Mayan city of Caracol in Belize, which is exhibited at the Penn Museum in Pennsylvania. Mayans used these stones to mark time. This stela, which shows an image of the ruling king, celebrates a date equivalent to May 10, 613 CE. The stone features an elaborate design that includes the ruler, his attire, and portraits of his ancestors. Besides the anthropological and historical significance of the stone, a thing that caught my attention is how the lines in the figure on the stone were traced.
The creators of the museum exhibit chose an LCD light projector that traces with white lines the contours of the design of the stone when you press a button and them untraces them after several seconds as is shown in the video.
I thought it would be interesting to film the tracing of the design by the projector in slow motion, but I was surprised by the video I obtained which showed the white lines of the stone flickering in a pattern that moved from left to right and that seemed to display occasional flashes of color. When I examined the video frame by frame, I found that the LCD projector did not use white light to create the lines at all. It used an alternating pattern of blue, purple (or red), yellow, and green lines to create the sensation of white lines. This pattern had an apparent left to right movement which maybe has to do with the very fast transition from one color to another..
These types of projectors are quite sophisticated, and if you are interested you can find an explanation of how they work here.
The photographs of the stela can only be used with permission of the author.