White light

[Strange]

 

Having photons of excited to different frequencies maintaining their inherent state and relationship and always combining to give the notion of white light seems to be more than random coincidence. If any group of photons loses energy then the continuous spectrum will be broken.

 

Why would they lose energy?

[Asimov]

Petushka: . I dont quite get it but I can answer your main question if I understand it correctly. It is no coincidence that white light always elicits white in our brain.The brain says so, not the white light per se...There can be some varience in the combination of frequencys and the mind can still say white. The red receptor cone signals red at 620 nm. Also at 750nm. A 620-750 range. Flourescents have a little more toward blue, incandescents tend to more red but both have what we call white light. Again, color is what our brain says it. In nature with no observer there is no color. I have barely normal color vision. A dark blue sock to you may appear to be black to me until I get into sunlight.You may see it as blue inside and outside. We are both correct. Black or dark blue. We determin the color. If one has trouble matching socks, boots are handy.Maybe most cowboys have bad color vision.

 

PS: How does one break a continuous spectrum?

 

A little fun here. Stare at a green background a minute, then look to the right on a white background. You will see red.The green receptors were temporaly bleached out. In this case the environmental light stayed the same but the color changed. Vision is perceptual and translates alOccipital cortex and company says so.

[petrushka.googol]

Supercontinuous sources exist for a given range.

 

What do you mean by all frequencies? Even a single source that does THz to UV is non trivial. If even possible.

 

And equal amount, amount of what? Photons, energy, intensity?

 

Photons.

[Strange]

Photons.

 

 

Equal numbers of photons at every frequency would mean greater energy at the blue end of the spectrum than red, so I assume this would not result in white light.

 

 

Physics does not rely on abstractions. I am trying to ascertain the cause as to why the combination of different frequencies in white light is essentially stable.

 

What do you mean by "essentially stable"? If you can't explain what you are asking, I don't see how anyone can answer it.

Why is it that the mixture is always perfect ?

 

What do you mean by "perfect"?

 

If any group of photons loses energy then the continuous spectrum will be broken.

 

Why would they lose energy?

Edited September 16, 2015 by Strange

[swansont]

 

PS: How does one break a continuous spectrum?

 

 

A filter, for one.

 

We have laser safety goggles/glasses in the lab, and for the ones for UV/blue or IR/red, you miss out on part of the visible spectrum. You can't see the colors beyond the cutoff. The IR ones, for example, make it hard to see anything red, which can be tough because a lot of indicator lights are red. When you take the goggles off, everything has a pinkish hue, because your brain has been filling in the light, assuming that the source is white — so it's been adding in red because there is no red light. Until it readjusts, it overcompensates.

[Klaynos]

We have laser safety goggles/glasses in the lab, and for the ones for UV/blue or IR/red, you miss out on part of the visible spectrum. You can't see the colors beyond the cutoff. The IR ones, for example, make it hard to see anything red, which can be tough because a lot of indicator lights are red. When you take the goggles off, everything has a pinkish hue, because your brain has been filling in the light, assuming that the source is white so it's been adding in red because there is no red light. Until it readjusts, it overcompensates.

It's always fun after wearing them for a good few hours.

 

Continuous number of photons from a source across the visible spectrum would be very blue in terms of energy and intensity. But as Swansont's post suggests it might not look blue to the human eye (because they're crap sensors). We still need to understand your questions a little more.

[imatfaal]

Real scientists really do see the world as if through rose-tinted glasses!

[John Cuthber]

Physics does not rely on abstractions. I am trying to ascertain the cause as to why the combination of different frequencies in white light is essentially stable.

Because , if the combination doesn't look white, we call it something else.

But the combinations are not "stable" in any meaningful way.

The first three spectra here

https://en.wikipedia.org/wiki/Fluorescent_lamp#Phosphor_composition

are completely different, but they all look fairly white because the eye is a very poor sensor.

[petrushka.googol]

From the most recent posts I'm inclined to conjecture that the "white" light that we receive from a source like the Sun is not always "White" (although as stated aforesaid the eye makes us believe otherwise).

 

Am I on the right track ?

[Klaynos]

The sun is a relatively temporally consistent source.

 

It never provides an equal number of photons at every frequency though.

 

Google, spectrum of sunlight.

[John Cuthber]

"From the most recent posts I'm inclined to conjecture that the "white" light that we receive from a source like the Sun is not always "White" (although as stated aforesaid the eye makes us believe otherwise).

Am I on the right track ? "

yes

[Asimov]

Actually seeing is in the occipital cortex. The eye sees nothing.A beautiful construct that takes lousy pictures that are"computer enhanced by our brain. Hubble was myopic , but computer enhancement cleared pictures a lot. It was later corrected. Expensive glasses! Sever the optic nerves and you see nothing though the eyes work fine.

 

Stare at a green square a while, then look to the right at a white wall.. You'll see a red square. Note that the colors are vastly different and the light frequency didnt change. After bleaching the green cones, the fresher red cones prevail and we call the same light red. So what color is the light? The observer determins that.

[petrushka.googol]

LOL. Phyisics is full of abstractions.

 

LOL Faux Pas.

[Klaynos]

The observer determins that.

That depends on how you define colour. If you define it as the frequency of light then the observer doesn't matter. That's not a very human way to define it though.

[petrushka.googol]

Actually seeing is in the occipital cortex. The eye sees nothing.A beautiful construct that takes lousy pictures that are"computer enhanced by our brain. Hubble was myopic , but computer enhancement cleared pictures a lot. It was later corrected. Expensive glasses! Sever the optic nerves and you see nothing though the eyes work fine.

 

Stare at a green square a while, then look to the right at a white wall.. You'll see a red square. Note that the colors are vastly different and the light frequency didnt change. After bleaching the green cones, the fresher red cones prevail and we call the same light red. So what color is the light? The observer determins that.

 

As a control let me put forward a "robot eye", designed to register colors based on frequencies and bandwidth. Would the above still apply ? Would "white" still be white ?

That depends on how you define colour. If you define it as the frequency of light then the observer doesn't matter. That's not a very human way to define it though.

 

But then here we are talking physics and optics.....

[Strange]

 

As a control let me put forward a "robot eye", designed to register colors based on frequencies and bandwidth. Would the above still apply ? Would "white" still be white ?

 

Not at the sensor (just like the eye). But modern digital cameras do a lot of post-processing (in their "brain") including automatic white balance, which means they can be nearly as good as humans at making the image look as if it was taken under "normal" lighting conditions. ("Nearly as good" might be an exaggeration...)

[Klaynos]

 

As a control let me put forward a "robot eye", designed to register colors based on frequencies and bandwidth. Would the above still apply ? Would "white" still be white ?

 

 

But then here we are talking physics and optics.....

You need a spectrometer and a mathematical definition of white.

[Asimov]

Petruska: Interesting idea, robotic eye. This would be a superior eye in some respects to an organic eye. Still, both are only cameras and see nothing, no color, no anything. The robot could be programmed to say red when exposed to red frequencies and could report white with certain mixes of light. The robot would need strong AI to actually see colors in it's computer brain.The red-green afterimage experiment wouldn't work as the robot wouldnt have cones that selectively bleach after firing too much. as the frequency of the perceived red and green are the same. We assign colors to certain frequencies but colors are determined by our perception of the frequency.

 

Dogs are dichromats. Two cones. They accurately identify many colors but not as well as us and we can never see like a dog even if we were dichromats. They overall access their environment well but rely more on smell and hearing. My poodle was blind at 6 months but people often dont detect this.Get a treat near him and he accurately homes in on it.

He smells better than I do.

[petrushka.googol]

Petruska: Interesting idea, robotic eye. This would be a superior eye in some respects to an organic eye. Still, both are only cameras and see nothing, no color, no anything. The robot could be programmed to say red when exposed to red frequencies and could report white with certain mixes of light. The robot would need strong AI to actually see colors in it's computer brain.The red-green afterimage experiment wouldn't work as the robot wouldnt have cones that selectively bleach after firing too much. as the frequency of the perceived red and green are the same. We assign colors to certain frequencies but colors are determined by our perception of the frequency.

 

Dogs are dichromats. Two cones. They accurately identify many colors but not as well as us and we can never see like a dog even if we were dichromats. They overall access their environment well but rely more on smell and hearing. My poodle was blind at 6 months but people often dont detect this.Get a treat near him and he accurately homes in on it.

He smells better than I do.

 

Lol. Although slightly off topic......

[John Cuthber]

That depends on how you define colour. If you define it as the frequency of light then the observer doesn't matter. That's not a very human way to define it though.

it's worse than that.

Pink and brown are colours.

Good luck to anyone trying to define the wavelengths.

[petrushka.googol]

From what I gatther the human eye can discern a max of 10 million colors. Differentiating a continuous spectrum to this accuracy is as close to "white" as we can get.

[Klaynos]

From what I gatther the human eye can discern a max of 10 million colors. Differentiating a continuous spectrum to this accuracy is as close to "white" as we can get.

But it doesn't work like a spectrometer. There are only 3 wavelength dependent types of sensor with broad overlap. That's how a TV can make lots of colours with only 3 colour emitters.

[petrushka.googol]

But it doesn't work like a spectrometer. There are only 3 wavelength dependent types of sensor with broad overlap. That's how a TV can make lots of colours with only 3 colour emitters.

 

What I'm trying to say is that the white we see is limited by our limited perception (10 million colors). If we had a better sensor (eye) capable of tapping say, 20 million colors what we interpret as white would possibly not be so.

[Klaynos]

It's more complicated than that. Because if the 3 overlapping sensors and complicated data processing that the brain does.

[swansont]

 

What I'm trying to say is that the white we see is limited by our limited perception (10 million colors). If we had a better sensor (eye) capable of tapping say, 20 million colors what we interpret as white would possibly not be so.

 

The thing is, if this is true (and again, you state this without support), we perceive these colors even if the source does not cover all of the frequencies of the visible spectrum (either because the spectral width of the sources are too narrow, or too wide). My display says it will do up to 16.7 million colors, but it can't give me a relatively pure color, corresponding to a spectral line of some atom, or laser, even if they are many MHz wide. The sources in a monitor are going to be tens of nm wide (which in the visible spectrum is about a million times wider than 1 MHz)

 

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