When I heard that Old Sacramento was premiering an event called Theatre of Lights, I pictured lasers shooting colored beams into the night sky. I figured that if I was curious, others would be too, so I’d better report. Theatre of Lights turns out to be a fun, 10-minute outdoor show where “Mark Twain” makes a rooftop appearance to give a short history lesson and reading of “The Night Before Christmas.” Special effects illuminate the façades of historical buildings and simulate the buildings’ trials in the face of fire and flood. Later, Santa shows up to bid a merry Christmas to all. The free show runs Thursday through Sunday at 6:30 and 8 p.m. through Jan. 3. Meet at the holiday tree at Front and K streets.