Art
The Strange Case of Missing Magenta
BY SOPHIA HURST
And other impossible colours Magenta doesn’t exist. Here it is! Magenta is made by combining red and violet – and if you know your visible light spectrum, one end dips into infra-red and the other into ultra-violet. Light travels in waves, and each colour has a different wavelength. Red and violet have such different wavelengths that they are on the very opposite ends of the visible spectrum, and because of that magenta is not on the visible spectrum at all! How is that possible? We can clearly see magenta, so why doesn’t it have a specific wavelength that we can find on the spectrum of visible light? If you take each end of the visible light spectrum and bend them around to create a ring, that’s where magenta lives: at where the opposite ends join. This may sound like a silly thing to say since quite obviously nobody alive is able to physically rearrange the fundamental order of visible light (I would hope), but it is actually closer to the truth than you would think. . At the risk of oversimplification, it makes sense for our wonderful brain to make up much of what we ‘see’. It fills in blanks
for our blind spots, filters the important information when our eyes move from one thing to another, and, importantly, makes up what the colour spectrum looks like. The human eye is made of up three types of photosensitive receptor cone cells that sense colour – they sense what we consider the primary colours of red, blue, and green. We call this trichromacy. This opens up a host of possibilities for … well… every single other colour we can’t actually see. Like yellow, which is a combination of sensing red and green wavelengths of light. There are animals that have yellow-sensitive cones in their eyes. That means that when light with a wavelength matching that of yellow hits the back of their eye, they experience yellow; goldfish, for example. Other animals only have two types of colour receptor cones – dogs are missing red cone cells. The evolutionary king of colour receptors is the mantis shrimp, with 12 different cone types. Having 12 different types of colour receptors does not give the mantis shrimp as much of an edge as one may think. Researchers from the University of Brisbane in Australia and the National Cheng Kung University in Taiwan trained shrimp to distinguish between different colours in exchange for food. When the wavelengths of the colours were quite far apart this was not a problem; they could individually react to them. However, when the shades of colours became closer together, the shrimp could not tell them apart. A human would not have had the same issue though, because we don’t rely just on our colour receptor cones to experience colour: we rely on our human brains. When light hits the back of our eyes and has a wavelength corresponding to yellow, our green and our red receptors are stimulated, but our blue receptors are not – and our brain can then take the relative information to give us the sensation of yellow. This is similar for all the different shades in between red, green and blue. It is not as if we can directly experience every single photon that hits our eyes – there are just too many and we would get very confused and distracted. Instead, our brains average out the signals they get and assign the signals with colour-experiences. For example, if two photons from the rubber duck that
8 IMAGE BY PHILIP RONAN, GRINGER; DISTRIBUTED UNDER CC-BY-SA-3.0 LICENCE.
