Wednesday, March 28, 2012

Red, Green, and Blue, part 4: Green or White

In the traditions of physics and mysticism, the source of all color is white. Here, I am saying that the base color of human vision is green. I am not meaning to contradict physicists or mystics. White is indeed a color of special cosmic importance. It is only on Earth and in the human experience of light that green is the first color.

Pure white is a mathematical definition that is particularly useful in physics, describing energy in which all wavelengths are equally represented. Among many other uses, pure white is valuable as an approximate description of the light given off by the sun. To mystics, pure white is the encapsulation of all energy and all information, and by extension, a completely absence of bias, point of view, and falsehood.

Alas, pure white is something we as humans will never see, at least not with our eyes. To begin with, the approximately pure white light of the sun does not make it to the ground. Only a relatively narrow band of wavelengths can make the trip all the way through the atmosphere to sea level. Ultraviolet is mostly filtered out in the ozone layer, so those wavelengths are absent in the “pure white” sunlight we see. Infrared is filtered out all along the way, and is not so well represented by the time sunlight reaches the ground.

The “pure white” light of the sun, by the time it reaches us, is light that has been through a series of filters to take out these wavelengths here, and those wavelengths there. It is still pure enough as far as we are concerned when we look at it, but in a larger sense, it is light that has been colored by its past experiences.

Sunlight at ground level is the light of the visible light band. And that means it is not much more than the light we know as green.

Sunlight as we see it on Earth, or any other white light we see, is merely green balanced out with blue on one side and red on the other. This is the white we see when we seen sunlight on Earth, or a white flower, or the white background of a computer window.

When you look at a spectrum graph of pure white light, it shows as a smooth, level line. But humans see white not as a matter of smooth or even, but merely as a matter of balance. Anything can look like a perfect white, if its spectrum is strong in green and about equally strong in blue on the left and red on the right. There can be extreme spikes and gaps in the spectrum, and we can’t easily tell as long as we are relying on our eyes.

In the extreme case, the white of a color video display is literally three narrow bands of color, one red, one green, and one blue, together representing about one fifth of the wavelengths of visible light. We can’t readily tell and don’t particularly care that four fifths of the wavelengths we are able to see are missing from video white. If we see green balanced out with blue and red, we will call it white.

This is all I am saying when I say that white comes out of green. Taking a broader view, it is easy to see the way that green comes out of white. When we look at green plants, we are seeing the approximately pure white light of sunlight which has been filtered through Earth’s atmosphere, then selectively reflected by the plants. In its physical production, this green is indeed nothing more than a reduced version of pure white.

I believe we see green so well because green is so important on Earth. But that, of course, is only a theory. The derivation of green from white is a physical effect that can actually be measured and demonstrated.