How do the lighting effects work?

 We were watching Stables at the Prospect Farm gathering.

This lighting effect looked strangely familiar. It is not far off being the diffraction pattern through a net curtain.

But then this one came up which had me wondering about mirrors like in a kaleidoscope,

There wasn't a brand name on the small cylindrical units that had 3 apertures. https://en.wikipedia.org/wiki/Laser_lighting_display does mention both mirrors and diffraction.