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Comment by mcv | Hacker News Reader

Fascinating. I've often thought about how purple relates to violet, but never really figured it out.

There are of course colours we call violet that we make by mixing red and blue. For example, the colours in this very article, which use RGB colours to mix red, green and blue light to create violet. So the violet in this article isn't "true" violet at all; it's just a faded bluish purple.

So are there real world paints that are actually violet? Or is the violet from the rainbow something we cannot truly reproduce, and only fake by mixing red and blue?

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White light contains light of all frequencies, so a violet paint that only reflected a single frequency would look very dark since it would only be reflecting a tiny proportion of the light that hit it. Even if it reflected a range of frequencies around violet it would still look very dark unless the range was large enough to also contain a lot of blue.

If you wanted to see "true" violet, your best bet would be to find a monochromatic violet light source. A Blu-ray laser would do the trick. But it won't look any different from the RGB imitation aside from being brighter.

EDIT: Please do not shine a Blu-ray laser directly into your eye.

How about a blacklight? The frequency of light you can see leaking through the filter is 404nm, so that should be a relatively safe way to see what "spectral violet" looks like, right?

If your white light source has a flat spectrum, then the violet paint wouldn't be any dimmer than any other color. The reason red or blue paint looks bright enough to see is because, as you said, they do reflect a range. So the violet paint could reflect the same bandwidth range as the traditional visible spectrum paints, and it would have the same power density.

Unless you mean appearance, in which case, yeah, our eyes don't detect violet very well.

It's also true of other colors that aren't red green or blue. They are 'faked' by mixing.

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