Find someone around you who hasn’t read the title of today’s email. Ask them what color the seats are in a movie theater. Chances are, they’ll say “red.” Google Image Search results for “movie theater” and “movie theater seats” will give you similar results; while not all of the chairs are red, most are, including images used by NPR (seen above), the Los Angeles Times, New York magazine, CNN, USA Today, Forbes, and many others. The reason for this is not a coincidence and it’s not a conspiracy. 

It’s science.

Our eyes have two different parts that help us detect the presence of light -- we have “rods” and “cones.” As Gizmodo summarizes, “[r]ods, which are the more numerous, are more light sensitive in general, but have no receptivity to color. Cones, on the other hand, are few and weak, but brings the color into life.” While these two parts have independent functions, they work in conjunction with one another. In a brightly-lit environment, the rods don’t need to do all that much and the cones get to do more -- imagine the visual cornucopia provided by a sunny afternoon in the spring. But when there isn’t as much light, the opposite happens; as Gizmodo notes, “the cones lose their grip on our vision and the rods take over.” Instead of our rains focusing on the rainbow of colors around us, it focuses our attention on finding light. Safety first, after all.

But when it comes to color, not all light is the same. Red light has a longer wavelength than orange light, orange has a longer wavelength than yellow, and so on and so forth all the way to blue, then indigo, and then violent. When our rods take over in low-light situations, the cones are still working, just not quite as hard. It’s easier for them to detect shorter wavelengths, so red is the first color we lose the ability to discern. This is called the Purkinje effect, named after a Czech anatomist who first articulated the phenomenon back in 1819. 

The Purkinje effect is hard to imagine in the abstract, and most of us aren’t sitting in a movie theater waiting for the lights to dim. That’s OK -- Wikipedia can help. Here’s an animated gif simulating the effect: