No Stupid Questions

So white light is when your brain sees a roughly matched signal level on all three color channels. So white would be all of whatever color receptors we evolved for the planet. It's more of a signal overload than a color.

We actually can't tell the difference between the mix of primary colors and the actual color. Take Cyan at about 490nm. Looking at it triggers your red, blue, and green receptors in a spefic set of levels your brain reads as Cyan.

However your brain can't tell the difference between a signal at 490nm and the right combination of 440, 540, and 580 nm. So for example a tv can only show 3 colors but your eyes and brain can't tell the difference between that and all the natural colors.

We are the most sensitive to green because it's the wavelength least used by photosynthesis and most plants reflect it. So we evolved to be extra sensitive to it. Camera sensors are usually 50% green, 25% red, 25% blue.

A small number of women have a mutation allowing them to see yellow. So some women can tell the side difference between true yellow and a primary color mix.

The sun is actually green

Nice recent kind of related video by Looking Glass Universe.

Yes. Kind of. Probably.

What we have is an issue with terminology. The thing is, "white" only makes sense when specifically referring to human vision.

Our eyes have cells (cone cells) that are tuned to specific wavelengths in the EM spectrum. Three different wavelengths - one set of cone cells peak at 560nm that we see as Red, one at 530nm that we see as Green, and one at 420nm that we see as Blue.

"White" is just our interpretation of a strong signal in these three frequencies.

If, everything else being equal, our cones cells responded to higher wavelengths that our eyes can't currently see, then our "white" might easily be what we see as "red" now, because we'd be also seeing the infra-red that we're currently not.

is white light "white" because that's what our start emits?

I'm going to say "no". Just because humans only see in the "visible spectrum" doesn't mean that all life on Earth does. There are creatures that can see in infrared spectrum such as:

• Snakes like pit vipers, including boas and pythons
• fish such as cichlids, goldfish, and salmon
• Mosquitoes
• vampire bats

There are also creatures that can see way past the other side of the "visible spectrum" into ultraviolet

• Bees like Bumblebees and Honeybees
• Butterflies
• Reindeer
• birds like European Rollers
• Scorpions
• Hedgehogs
• even dogs and cats

So as you can see from these lists its not just a specific genus or species. Many of our mammalian cousins can do this. Given that many other species have evolved this ability, it just wasn't evolutionarily needed for humanity to survive.

White light is just white cause our sun blasts out a big rainbow mix that our eyes evolved to handle. But like, imagine we grew up orbiting a chill red dwarf star instead.. our eyes would be all tuned differently, vibing mostly with reds, making red our new "white." Even our language and color wheels would shift, calling reddish hues "neutral." Wild thought: even crazier when we're still perceiving this existence through our own lens.

There are many colours of white, usually measured by temperature in kelvin. Mid day sun is a different white to late afternoon. With different sun temperatures, you would see different whites, the hotter the star, the bluer or cooler the white. The colder the star, the redder or warmer the white. Our eyes/brains do a great job adjusting white balance so the effect isn't super obvious until you start comparing warm/neutral/cool whites in interior lighting

Having had to manually white-balance the cameras in broadcast journalism classes in college, I love this question. Wish I knew the answer, but commenting so I will remember to check back in.

No. Red is a single wavelength, we call red to anything that emits light waves with length between 625 to 750 nanometers, green anything between 500 to 565 and blue anything 450 to 485.

White is not real, white is what your eyes percebe multiple wavelengths together, if we had evolved near a red dwarf, there would probably be less blue light so out white would likely be independent of blue, just like it is independent of UV currently (because we don't see those wavelengths).

Curious thing is that purple is also not real, purple is what your brain interprets blue+red, which are two separate wavelengths, so it's not a color like red or green, but rather an illusion that your brain creates to show you red and blue at the same time.

In general objects that appear to us as white either emit a mix of waves with different wavelengths in such a way that we perceive the total of it as roughly equally blue, red and green or reflect all the light that hits them diffusely. So white will always be white since it just means cone triggering equilibrium. Even if your primary colours change.

Fo light emitters it's a bit complicated and partly depends on if our cone cells which are responsible for colour reception would have evolved differently.

With our current sun and atmosphere they have evolved to perceive a range of wavelengths that are the most abundant/intense and don't have a drop in intensity in the middle. Here is a graph showing solar and terrestrial wavelength intensities compared to wavelengths we have evolved to see.

credit

So to find out if the range of wavelengths we are able to see would be different if our star were a red dwarf we would need to take the emission spectrum of the star you'd want to replace our star with(the orange part), then remove from that the percentages of each wavelength that our atmosphere absorbs to get the terrestrial wavelength intensities (the dark blue part).

Then you could probaly look at that graph and take a chunk out of the Y-axis that covers the highest intensity wavelengths (cause plants would probably have that colour and we'd want to see those) while not getting too long and also trying to avoid lower intensity dips in wavelength. Then you've got your visible colour range. If that range is the same as our current one then white always stays white.

However for light emmiting objets depending on if the visible colour range we now perceive is different, our cone cells would also now be triggered at different wavelengths meaning that some stuff that emits roughly an equal amount on each wavelength our cone receptors can perceive which we before saw as white, we would now perceive as colourfull. However all of the natural white light emitters in nature are perceived as such because they are blasting out light on the whole wavelength spectrum basically. So even if our cone cells shifted they'd still be triggered equally and the object would still appear white.

As for the objects that reflect the light diffusely, it would depend on whether they actually absorb some wavelengths that just were outside of our visible wavelength range before. If they do then we would now perceive them as having a colour and if they still diffusely reflect all the wavelengths of now visible light they'd still be white.

Edit: fixed the implications for white perception Edit2:actually answered the questions, structure

Here's another one: is your 'white' the same as mine? Because of differences in physiology and our unique makeup of our individual bodies and nerve pathways, could what you see as 'white' be the same set of neural signals I perceive as 'red'? Our behavior (e.g. stopping at a 'red' light) would be conditioned similarly, even though our individual neural interpretations could be different, even if the measurable phenomenon like wavelength were objective.

There are other better answers here already.

But you got me wondering, how red are red dwarfs really? Maybe they're just like a few % more red than our sun, but I bet they're still quite broad band.

So you maybe could have a similar range of colour reflection and absorption. And maybe there's enough R,G,B to saturate the receptors. I assume white is just that, when all color receptors are near saturated.

The eyes might not need to differ much, the brain can probably do everything in post processing anyway. All evolution needs to do to your eyes is to gather enough raw data that your brain can learn to differentiate, food, water, danger, things to breed with, and so on.

Maybe reduce the sensitivity of red receptor a wee bit, or maybe not, if plants are still absorbing lots of red, and we live amongst plants . . .

No, white is a broad spectrum phenomenon? Like, what we see as white is made up of red and other colors too overlapped