There was a scene in 1999’s The Mummy, one of the last movies in which Brendan Fraser was still acceptable as a leading man, in which our heroes enter into a dark tomb. A single ray of sunshine is peeking through the ceiling, and Fraser’s character, presumably familiar with ancient Egyptian interior lighting solutions, shoots a mirror. That rotates the mirror to the proper angle to reflect the sunlight across several mirrors in order to illuminate the entire cavernous room. Despite the improbability of the sun being at the correct position and a bullet knocking the mirror to the right angle, it’s a fun scene. Dr. Michael Mentink thought it was more than just movie magic, and decided to replicate the mirror lights in his own home.
Dr. Mentink chose to tackle this project because their own home is facing in a direction that allows very little sunlight to come through the windows. They were tired of the lack of natural light, and so they turned to imagined ancient Egyptian lighting techniques for a solution. Achieving this is a bit like trying to bounce your cue ball of a rail in order to knock the eight ball into a pocket — it’s all about the angles. But, as you’ve probably noticed, the sun doesn’t remain stationary from our earthly perspective. As the sun moves across the sky, you have to adjust the angle of the first mirror to compensate. During the time of the pharaohs, this would have required the use of a very attentive slave. Fortunately, we have technology today that renders the use of slaves unnecessary.
For this setup, a tracking mirror was placed in the garden where it is exposed to plenty of direct sunlight. That reflects light onto a fixed mirror mounted to the fence in the garden, which then shines light through a large window onto the floor inside where it can be dispersed. The only part of the system that needs to move is the tracking mirror, and that works a lot like a motorized solar panel mount. The tracking mirror is mounted to its wooden frame with a universal joint and is tilted as needed by a pair of stepper motors with long lead screws.
Dr. Mentink originally planned to use a development board, such as an Arduino, to control the stepper motors and position the mirror. But, they instead chose to control the stepper motor drivers from a computer directly through USB-to-UART converters. That let them write a program in LabVIEW to handle positioning and logging. Simple limit switches are used to zero each axis. The LabVIEW program sets the position of the tracking mirror according to the current time, rather than detecting and following the sun itself.
This isn’t the way we would normally expect to see someone tackle a project like this, but it does seem to work — and doesn’t require that Dr. Mentink hire a slave or fire a gun in the garden.