Light and Pigment

My friend recently purchased one of those trippy light fixtures that makes red, green and blue waves on the ceiling. It’s very relaxing. Looks something like this.

Red, green, and blue light swirling around on the ceiling of a room.
Beautiful demonstration of RGB color.

As I watched it, I noted how well those colors work together in a lightshow. That got me thinking about the differences between color interactions in light and pigment.

As you may know or remember from my first blog post on the science of paint, pigments are colored solids that give paints and inks their hues. The color wheel we all learned in art class is based on pigment colors. Red, blue, and yellow are primary colors. Orange, green, and purple are secondary colors. Humans in antiquity observed the properties of pigments as they mixed and inscribed this knowledge into the color wheel we know today.

A color wheel featuring the three primary and three secondary colors.
A color wheel.: Arbitrary human invention? Or a record of pre-existing natural laws?

However, there is another way to understand color. In fact, there are two ways. First is another pigment-based method. In printer inks the primary colors are cyan, magenta, and yellow (still close to the red, blue, and yellow of the classical color wheel). All other colors are made with those three, with varying levels of black added to achieve darker shades. In design, this is known as CMYK color (K is black). The far more modern way to conceptualize the color wheel is the light color wheel. Its primaries are red, green and blue. All colors combine to create white. This is called RGB color. Cyan, magenta, and yellow are secondary colors in RGB color. Screens use RGB color.

RGB verses CMYK color wheels.
RGB verses CMYK color wheels.

RGB color is considered additive because the way the colors are mixed is by adding together different colors of light. CMYK color by contrast is subtractive, because combining all CMYK colors yields the darkest black, and all other colors are created through lower levels of the base colors.

That screens use RGB is not an arbitrary choice by the inventors of computers. The reason screens must use RGB color is because light itself follows RGB color. Think back to if you ever played with a prism as a child. When it catches white light from the sun, it projects a full rainbow into the room. This is because white light is composed of all other colors of light mixed together.

On the contrary, think back to art class as a child. If you mixed all the colors of paint together, you’d get a grey, brown, or black. This is because paints are a subtractive color system.

The systems we use to manage colors are well known to any good artist or designer. And yet, these are based on scientific ideas, namely the properties of physical pigments verses light. Artists may not always fully consider this scientific knowledge, but they are at the very least unconsciously aware of it.

Perhaps the reason that red, blue, and green lamp is so relaxing is because of these properties of light. As the colors mixed together, you could see the different secondary colors flowing in and out and even a few bits of white. Whether its allure is based in science for others, now it will evoke that knowledge for me every time I see it. Plus… It’s pretty.

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