How many colours are there in a rainbow? Dad’s need to have a broad general knowledge. We get asked questions spanning everything from helicopters to bogies.
Therefore, in part two of Hero Dad, I’ll equip you with the grey matter ammunition you need to thwart the oldest of school myths.
Most people will answer the rainbow question with seven. Red, orange, yellow, green, blue, indigo and violet.
But this isn’t telling the whole truth, because a rainbow is a natural manifestation of something we’ve known for over 400 years. Isaac Newton demonstrated that white light (from the sun in this case) could be broken up into its constituent colours by dispersing it through a prism. The rain itself is acting as the prism that creates a rainbow.
If you look at a rainbow you’ll see the colours are not defined, rather they’re blended together. Therefore, the rainbow is an amalgamation of every colour within the spectrum of light radiated by the sun. Or at least, the part of it that actually gets through Earths atmosphere.
Hence the question becomes how many colours can we actually see from that spectrum?
How many colours are there?
Broadly speaking, there’s as many colours as there are possible molecules made up from combinations of atoms. As you can probably imagine that’s a pretty big number.
Visible light and therefore all the colours within, are actually a specific potion of the electromagnetic spectrum. Every molecule absorbs certain wavelengths of light from the spectrum, while reflecting the rest of it away. That’s the same spectrum that encompasses radio, x-rays and microwaves etc.
Thus, you interpret an object to be a particular colour because that portion of light from the visible spectrum is reflected back to your eyes. So the limiting factor is actually how many colours your eyes can see.
There’s No Eye in Rainbow
In bright light our eyes interpret colour using a collection of cone shaped cells, each sensitive to a different band of wavelengths. Most humans have three or four different types of cones, with each recognising around 100 colours.
Each receptor will be active or inactive in a similar way to how pixels on an RGB television screen work to display colour. The TV will use a mixture of tiny red, green and blue lights to form colours.
If we consider every possible combination of receptors being activated then, the maths would be 100 to the power of 3 (or 4) potential colours. That means most of us can see anywhere between a million and 100 million different colours!
People who suffer from colour blindness lack one the types of cone cells, reducing the number of colours they can see accordingly.
A Colourful Conclusion
How many colours are in a rainbow? Bloody loads, certainly more than seven.
How many can we actually see? The majority of us will fall somewhere around the million mark. Gifted individuals with a fourth type of cone cell considerably more.
So there we have it. You can now go back to your kids and blind them with science. That’ll teach them to ask silly questions, right?
And next time they come home from school reciting the colours of the rainbow, be sure to phone their teacher immediately and ask why she forgot the rest of them.
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