Colors vs depth & 2 other questions

[MyDiveLog]

You guys are great, and helped clear up my thinking. I gave him much the same story, and your commentary along with Xanthro's website reference, confirm what I'd heard.

His rebuttal was something like "Yeah, but don't Indigo and Violet contain red?" I know that they are distinct, and at different wavelengths....but why, when my kids mix blue & red, do they get these colors?

Sorry to belabor the point ... not really looking to contradict him, but rather to understand this intuitively.

 

[Xanthro]

For the record, I am not trying to be argumentative. I am trying to be helpful. I really do this stuff for a living.

The absorption by the water itself actually is very important in the red wavelengths. To say it isn't is just not true. Water absorbs red very strongly and this is easily noticable to any diver.

Just to put a real number on it, a layer just 1 m thick of pure water would absorb 35% of incident irradiance at 680nm (red light). I got that right out of a textbook I had laying on my desk. This is why you can't see red at depth when diving unless you use your dive light.

What I think is confusing you is that in the blue/shorter wavelength part of the spectrum water is a very weak absorber and in that region you are right a diver would not really be able to notice its effect. Then the particles and dissolved materials are what you will notice like you suggest. If there aren't many of these things in the water it will look blue (like clear tropical waters). If there are lots of these things in the water it will usually look greenish or brownish (like in New England where I live).

I wasn't even attempting to break the absorbtion down into wavelength, since again, this as way to complicated an answer to the original posters question.

Obviously if water didn't absorb red and longer wave length, water wouldn't heat up.

My intent was to peak the interest of the original poster, not to create an academic discussion.

I've found on other boards, that if you get too technical, the poster often doesn't either understand, or care to read the reply. Some people don't want to feel they are in school after asking a simple question.

I do like to peak someone's interest, with a bait of information, and then provide them with a link to follow up, so the poster can determine how far to bit into the topic.

Xanthro

 

[Xanthro]

You guys are great, and helped clear up my thinking. I gave him much the same story, and your commentary along with Xanthro's website reference, confirm what I'd heard.

His rebuttal was something like "Yeah, but don't Indigo and Violet contain red?" I know that they are distinct, and at different wavelengths....but why, when my kids mix blue & red, do they get these colors?

Sorry to belabor the point ... not really looking to contradict him, but rather to understand this intuitively.

The colors for light and pigmentation are very different.

For example, in light, black is the absence of all color, and white is a mix of all visible light.

It's the opposite if you mix colors together in paint. White is no color, and black is a mix of all primary colors.

Plus, pigments are based on primary colors. By mixing the three primary colors, you create other colors. By mixing these secondary colors, you can create even more colors.

It's not uncommon to think violet contains red, because as your instructor and childern see, when we mix paint, we use that red to see violet. What we are really doing in mixing the paint, is absording the red, so we don't see it, and when we absorb all the colors but violet, we see only violet.

The colors you are mixing, really just change how the light is absorbed and reflected back, so you see changes in color.

Light itself does not work like this. You can't mix light in the same way. Mixing blue and red light, does not make violet light. The color we see from light is determined by the lights wave length, mixing light together doesn't change this wave
length.

When light is refracted in a prism or rainbow, it does so in order of wave length, ROYGBIV.

I hope that helps, and if you need more detail, please let me know.

Disclaimer, this is at a very low level of explaination, and I understand from a higher level technical point of view, it's not prefectly correct.

 

[RichLockyer]

but why, when my kids mix blue & red, do they get these colors?

When light waves are mixed to form a new color, the interaction of the frequencies results in an actual change of the fundamental frequency. Once formed, you can no more remove the red from violet than you can remove the "E" from a C-major chord.

 

[rcohn]

The colors for light and pigmentation are very different.

For example, in light, black is the absence of all color, and white is a mix of all visible light.

It's the opposite if you mix colors together in paint. White is no color, and black is a mix of all primary colors.

Plus, pigments are based on primary colors. By mixing the three primary colors, you create other colors. By mixing these secondary colors, you can create even more colors.

It's not uncommon to think violet contains red, because as your instructor and childern see, when we mix paint, we use that red to see violet. What we are really doing in mixing the paint, is absording the red, so we don't see it, and when we absorb all the colors but violet, we see only violet.

The colors you are mixing, really just change how the light is absorbed and reflected back, so you see changes in color.

Light itself does not work like this. You can't mix light in the same way. Mixing blue and red light, does not make violet light. The color we see from light is determined by the lights wave length, mixing light together doesn't change this wave
length.

When light is refracted in a prism or rainbow, it does so in order of wave length, ROYGBIV.

I hope that helps, and if you need more detail, please let me know.

Disclaimer, this is at a very low level of explaination, and I understand from a higher level technical point of view, it's not prefectly correct.

White and black are the same color, it's really the luminance that changes.

While you are very correct that mixing colors does not creat a new wavelength of light, it is the interation with the human tristimulus visual system that causes us to perceive a different color. For example, red and green light mixed will appear yellow because it stimulates the cones in the retina at that same relative levels as actual yellow light would. So pure violet light contains no red, but a mix of blue and red light might have the same appearance.

Ralph