Here is a room you can never fully light with one light

In photography, light is everything. After all, that’s the key part of its very name. When taking photos indoors, there are many setups you can make with just one light. And did you know that, in theory, almost every room will be lit no matter where you place the light?

However, here’s something I’m sure you’ll find interesting. When there are mirrors on the walls, any room shape will be fully lit but one. It’s called the Penrose unilluminable room, and in his video, Steve Mould talks about this interesting phenomenon.

This illumination problem is one of the classic math problems that was originally attributed to Ernst Straus in the 1950s. He asked if a room with mirrored walls can always be illuminated by a single point light source. If you’ve ever entered a mirrored room like the one below, I’m sure you noticed that the answer was yes.

In 1958, British mathematician and physician Roger Penrose solved the problem. Using ellipses, he formed the Penrose unilluminable room which will always have one area left in the dark, no matter where you place the light. George Tokarsky and David Castro proposed the solution using polygonal rooms in the 1990s, but Steve only examines the Penrose room so we’ll stick with it today.

Steve made a real-life model of the Penrose room. In his video, he demonstrates how the light behaves when it changes its position. He also relies on simulations and mathematical explanations to make the concept even clearer. But being a visual type (and very bad at math and physics), I must admit I prefer the practical demonstration. :)

James of The Action Lab also made a video on this topic and 3D-printed his own Penrose room. He demonstrated another interesting trait of it by submerging it in water. When introducing vibrations, even the water waves behave similar to light waves, only traveling to certain points of the room.

Although chances are slim that we’ll ever take photos in a room like this, I still find this very interesting. Demonstrations like these could help us understand the nature of light. Or, at least, they can get non-scientific minds like mine interested in physics and math a bit more.