How are colourblind people able to recognize the colours when they put on the special glasses, they have never seen those colours, right?

Question

How are colourblind people able to recognize the colours when they put on the special glasses, they have never seen those colours, right?

In: Biology

Answer 1

You have color receptors in your eyes known as ‘cones’. These cones are tuned to one of three different wavelengths of light (generally, red, green and blue). They react most strongly to the exact wavelength of their tuning, but they also react less strongly to color near that wavelength.

Lastly, you have ‘rods’ which detect overall brightness.

So let’s say I shine a pure yellow light in your eyes. Your rods will give you a clue about how bright the light is. To determine the color, your red cones will detect the yellow light as somewhat distant (dim), your green cones will detect the yellow light as relatively close (bright) and your blue cones will detect the yellow light as somewhat distant (dim). The combination of all this information allows you to guess ‘yellow’ as the color of the light.

However, while this system works fairly well for pure wavelengths of light, it doesn’t have enough information to accurately describe an entire spectrum of light. In essence, you’re just making ‘best guesses’ at what mixture of color you’re staring at.

In (most) colorblindness, the issue is that two of your cones are tuned to wavelengths that are abnormally close to one another.

To understand why this causes a problem, imagine we’re playing a game where you try to find me. I tell you how far away I am from New York, Chicago and Los Angeles. With that information, you should easily be able to triangulate my location in three dimensions.

But what if I instead tell you how far away I am from New York, Chicago and Milwaukee? The fact that Chicago and Milwaukee are practically on top of one another means that I’m really giving you information that looks a lot more like two points of data (New York and Chicago/Milwaukee) than three points of data. It becomes much harder for you to locate me because even small errors can confuse the results.

The same is true when your cones are tuned to the ‘wrong’ wavelengths.

What color correction lens do is they block wavelengths located in between the too-close cones to reduce this confusion. As a result, your eyes receive an additional bit of information: a known dead zone. So instead of color wavelengths in that range being easily confused, you don’t see them at all and instead rely on the color ranges you can easily discriminate.