The idea emerged while playing around with diffraction foil on New Year's Eve. Besides multiplying fireworks a diffraction grating decomposes light by wavelengths, allowing you to perceive the spectral composition. But what if you could control a light source so the interference will magically decompress a colorful line of light into a rainbowy display floating in the air?

RGB stripes are unfortunately not enough to display 5x7 pixel characters because each color translates into one row of pixels. So let's add hyper red, amber, turquoise and hyper blue for a sufficient resolution of 7 colors. HrRAGTBHb is already painful enough to spell out, so I didn't want to wire up more than one set of LEDs and opted for a PoV setup instead. A spinning reflector with two exit holes redirects the light to avoid balancing and powering rapidly rotating electronics.

Here's a video:

Everything was printed from PETG at .3mm height with a .6mm nozzle on a MK3S because we wanted to find out if it works as fast as possible. Even the huge rotating reflector fits (that's why it's oval). Free of supports except for the ones shown in the screenshot and a few internal mounting holes. Orientations should be obvious.

A .2 height or less would have been better for the reflector because I used some "Kexcelled K5-shade: light shield" filament so no light is visible through the walls. It does it's job well but was somewhat challenging to print because of the extremely high content of pigment. It also stained the textured build plate and I had to print a slab at elevated bed temperature to clean it.

The knob has some exposed gyroid infill to distract from the cheap motor driver.

Prusament PETG profile.

More info considering the electronics & code on Hackaday:

https://hackaday.io/project/180283-hololamp-between-display-concept-physics-class