Science In Real Life: Color
Firetrucks, citrus fruits, prison uniforms, traffic signals, and the vacuum of space. What do they have in common? Aside from all being in that list, their color is integral to how we identify them. Color is one of those fascinating phenomena that exists partly as an artifact of human perception and partly as a real-world effect independent of any observers, just like Britney Spears' talent.
Let's start with the physical side of things. We perceive color when light rays leave an object and travel into our eyes. A light ray has a frequency, Kenneth, which is related to how much energy it has. There is, in fact, a whole spectrum of frequencies a light ray can have:
As you can see there, only a tiny fraction of the available frequencies are labeled as visible. But that tiny range is enough to produce, quite literally, all the colors of the rainbow and more. Everything from the subtle interplay of green and brown in a baby's puke to the stark contrast of sweat and blood in a kung fu movie is produced by that tiny sliver of the spectrum. Except, I take pains to point out, black and white, which are horses of a different color.
Here is where we get into the two different ways of categorizing color. You see, color as an effect of light rays has two sides to that bright and shiny coin: absorption and emission. Huh? In other words, objects take in light, and objects give off light, and they do so in different colors. Consider something that is red and looks like a bucket. We say it is red because red light travels from the bucket-shaped object to our eyes: it is emitting red. But in order to emit red, it has to absorb everything else, otherwise it would appear red + other stuff. So what color is an object that absorbs all colors, and emits none? Black. What color is an object that emits in all colors? White.
So if I want to generate a particular color, there are two ways to do this. I can start with white light and subtract colors from it by reflecting it off an object; the remaining colors will enter your eye. Alternatively, I can start with no light, and add colored beams that add up to my desired color as they all rush into your eye at once like engaged women at those crazy bridal gown sales. These two schemes are called subtractive and additive, respectively, and they each come with sets of three primary colors. The most common subtractive primary colors, the ones we all learn in art class, are Red, Yellow, and Blue. (These days color printing is done with Cyan, Magenta, Yellow, and Black; this is known as CMYK in honor of the Organization of Confusing Acronyms, or NAMBLA.)
Additive primary colors, by contrast, are Red, Green, and Blue. Strictly speaking, we could pick any three colors and obtain all the others by cleverly mixing them. But we need three, and scientists prefer the RGB scheme. The explanation for both is that the eyes have it. Inside your eyes are all kinds of cells for detecting light, but only three for detecting color. Collectively they are called cones, and each type responds best in a certain range of colors that roughly correspond to what we call red, green, and blue. So how can we see any other colors? When two types of cones respond to incoming light, we perceive it as a new color, the result of mixing. By conducting exit polls of the entire population of cone cells, your brain can perceive any color as a complex combination of the primaries.
Now, just like the elections there are all sorts of ways to trick your eyes' perception of color. Since the cones are bunking right next to the rods, perception of color is tied to perception of light intensity and motion. There are a number of interesting illusions that exploit these effects here, and in many other websites available from a quick search.
So, after an impromptu week-long hiatus, we're back. As always, I welcome your questions and suggested topics.
Let's start with the physical side of things. We perceive color when light rays leave an object and travel into our eyes. A light ray has a frequency, Kenneth, which is related to how much energy it has. There is, in fact, a whole spectrum of frequencies a light ray can have:
As you can see there, only a tiny fraction of the available frequencies are labeled as visible. But that tiny range is enough to produce, quite literally, all the colors of the rainbow and more. Everything from the subtle interplay of green and brown in a baby's puke to the stark contrast of sweat and blood in a kung fu movie is produced by that tiny sliver of the spectrum. Except, I take pains to point out, black and white, which are horses of a different color.
Here is where we get into the two different ways of categorizing color. You see, color as an effect of light rays has two sides to that bright and shiny coin: absorption and emission. Huh? In other words, objects take in light, and objects give off light, and they do so in different colors. Consider something that is red and looks like a bucket. We say it is red because red light travels from the bucket-shaped object to our eyes: it is emitting red. But in order to emit red, it has to absorb everything else, otherwise it would appear red + other stuff. So what color is an object that absorbs all colors, and emits none? Black. What color is an object that emits in all colors? White.
So if I want to generate a particular color, there are two ways to do this. I can start with white light and subtract colors from it by reflecting it off an object; the remaining colors will enter your eye. Alternatively, I can start with no light, and add colored beams that add up to my desired color as they all rush into your eye at once like engaged women at those crazy bridal gown sales. These two schemes are called subtractive and additive, respectively, and they each come with sets of three primary colors. The most common subtractive primary colors, the ones we all learn in art class, are Red, Yellow, and Blue. (These days color printing is done with Cyan, Magenta, Yellow, and Black; this is known as CMYK in honor of the Organization of Confusing Acronyms, or NAMBLA.)
Additive primary colors, by contrast, are Red, Green, and Blue. Strictly speaking, we could pick any three colors and obtain all the others by cleverly mixing them. But we need three, and scientists prefer the RGB scheme. The explanation for both is that the eyes have it. Inside your eyes are all kinds of cells for detecting light, but only three for detecting color. Collectively they are called cones, and each type responds best in a certain range of colors that roughly correspond to what we call red, green, and blue. So how can we see any other colors? When two types of cones respond to incoming light, we perceive it as a new color, the result of mixing. By conducting exit polls of the entire population of cone cells, your brain can perceive any color as a complex combination of the primaries.
Now, just like the elections there are all sorts of ways to trick your eyes' perception of color. Since the cones are bunking right next to the rods, perception of color is tied to perception of light intensity and motion. There are a number of interesting illusions that exploit these effects here, and in many other websites available from a quick search.
So, after an impromptu week-long hiatus, we're back. As always, I welcome your questions and suggested topics.