We made an 1800s lighthouse lantern, and it works.
This is a functional 6th-order Fresnel lens replica, the smallest size used in real 19th and 20th century lighthouses. The entire design was 3D printed on the Formlabs Form 4 print ecosystem.
The lenses and catadioptric prisms are printed in Formlabs Clear V5. To get the optical clarity required to properly refract light, we wet-sanded every part to remove layer lines and finished them with a buffing process to achieve a glass-like finish.
The structural frame is printed in Formlabs Black V5, and the gears are printed in Tough 2000 V2, chosen for its high stiffness and creep resistance to support the weight of the solid resin lenses.
Everything is entirely custom-designed in CAD (Onshape). The refraction angles were manually calculated and ray traced for each individual prism so the light perfectly collimates into a horizontal beam.
Because a 6th-order lens is still quite large, the frame was designed to print in several pieces and assemble with dovetail joints.
It actually spins using a 12V DC gear motor with a 6:1 gear reduction system, rotating the lens at around 6 RPM on a lazy susan bearing. The mechanism is friction-driven, so the center of the base stays completely hollow, letting a stationary 12W dimmable vintage Edison bulb sit inside.
The lens takes the expanding light from the bulb and compresses it into a highly focused horizontal beam, creating that classic lighthouse "loom" sweeping across the room.