This is a post I began quite some time ago thinking it would be a quick and easy one, since it concerns a topic I know very well.
But — perhaps due to my own inability to be brief — it turned out to be more involved than expected. Maybe I just have a hard time leaving out all the details. In any event, I set it aside until I had more time.
Then I had an idea for making this post a bit more fun (at least for me). The problem was: I needed to build a theatre! You see, this post is about color and light.
You may recall how I stumbled into theatre lighting in high school. By then I’d also learned a bit about photography.
(I had a photography class in junior high school. Our teacher was a former photographer from Life magazine — he taught us about taking covert photos in secured areas!)
Then in college I got into television and film production.
One thing those all have in common is color. In theatre — and to a somewhat lesser extent in TV and film — the light used to light the stage or studio or set is often colored. It’s more common to use white light in television, in part, due to the poorer ability of video cameras to distinguish subtle variations in color.
Film cameras do better, but the eye is very powerful when it comes to picking up color and light variation. Just think how breath-taking fall colors are and how you’ve never seen a photo that quite captures the subtlety of the stunning variations and shades.
I’ve apparently been fascinated by light all my life. My first word was “light,” and as an infant I was enthralled by watching lights at night. Apparently I would rarely sleep in the car during a night drive; I wanted to watch the passing lights!
To this day one of my small pleasures is sitting some up high and looking at city lights.
So let’s talk about light and color.
You may have heard that white light “contains all colors.” This isn’t always 100% true, but it is correct that most forms of white light do contain all the usual colors.
The sun’s light is the best example. A prism can “split” this light into a rainbow of colors. In fact, a rainbow (in the sky) comes from the sun’s light being split by drops of water. You can even see mini-rainbows in the spray of a water sprinkler.
However, for our eyes, it only requires mixing (adding) red, green, and blue light to make white light. The image to the left is a schematic of this.
If you could project three spotlights, one red, one green and one blue, on a screen, you would see something very similar to the above.
In fact, I did that way back in high school, and I gotta tell ya, it’s mind-blowing to stand in a dark theatre and to see white light appear where the three richly colored lights overlap.
(It’s also kind of weird that adding red and green gives you yellow. The cyan and magenta at least make some sense.)
Our television, video and color phone displays do exactly the same thing. If we use a magnifying glass to look very close, all we see is red, green and blue pixels (pixel = picture elements).
Go ahead and try it. You can probably see them if you just get very close — nose on the glass close.
Note that, in order to see all three pixels light up, you need to look at something white or close to it. (Technically, a pixel consists of a red and a green and a blue.)
Because red, green, and blue add to make white, we call these three colors the primary colors. And the process of adding them to make other colors is called additive. Strictly speaking, these three are the only primary colors, although some people use the term primary to refer to any bold color. In particular, you often hear yellow or even purple referred to as primary.
But they actually aren’t.
In the diagram above, note that the two I mentioned, yellow and purple (magenta is its proper name) are formed by adding two of the primaries. We add red+green to get yellow, and you add red+blue to get magenta. The final one, a light blue-green, called cyan, comes from adding green+blue.
These three, yellow, cyan and magenta, are called the secondary colors. Each secondary contains two of the primaries.
A color image in a magazine is made by starting with a white page and using transparent colored ink to subtract the necessary colors to create the desired color. The diagram to the left shows a schematic of this.
A very important difference is that this diagram subtracts the colors. Rather than three lights shining on an unlighted screen, this diagram represents colored filters in front of a lighted white screen.
Printers use yellow, cyan and magenta ink (each page is printed three times to lay down a color). Films and photo paper use yellow, cyan and magenta dye in three layers to achieve the same effect.
That printers use these colors may, in part, have led to calling them primary. It’s also confusing in that they sometimes call cyan “blue” and magenta “red,” thus making the printers’ primaries yellow, “blue” and “red.”
(Printers usually also use a fourth layer, black, for text and darker shadows in photos. Printers’ inks are fairly sloppy color filters, so color photos have muddy shadows without some black ink.)
Note that when we apply all three secondaries, we get black. This is because we’re subtracting all color from the white page.
(However, as I just mentioned, the quality of the color filtering is important. The worse the filtering, the muddier the colors, especially shadows.)
Essentially, the secondary diagram is a color negative of the primary diagram. Blue is the opposite of yellow, green is the opposite of magenta, and red is the opposite of cyan. (And vice-versa in all cases.)
Also, black (no color) is the opposite of white (all colors). In all four opposites, mixing them gives us white (for example, blue+yellow gives us white).
Another way to look at this is that yellow is the absence of blue. A yellow surface is yellow, because it absorbs the blue and reflects the red and green (that is, the yellow). Yellow ink or dye absorbs the blue and lets the red and green through. Likewise, magenta is the absence of green, and cyan is the absence of red.
Plants are green, because they reflect green light (they don’t use it), but they do absorb and use red and blue. So grass is green, because chlorophyll doesn’t need green light, and the sky is blue because dust in the air scatters blue light.
You might be wondering exactly what color is. The simplest analogy is to say that, if light was sound, then color would be pitch.
The color of light is its frequency (how fast it’s vibrating). Blue has the higher “pitch” (frequency), and red has the lower (green is in the middle). Infra-red is “lower pitched” than red, and ultra-violet is “higher pitched” than violet (which is above blue).
Radio waves, x-rays, micro-waves and gamma rays are all also light. (That is, they are made of photons, just as light is.) They have frequencies far outside the “visible light” band (radio waves are lower “pitched” than light, x-rays and gamma rays way, way higher).
Count your blessings your retina doesn’t see radio waves as visible light. If they did, it would never be dark no matter how hard you closed your eyes. Radio waves go right through you!
The frequency (pitch) of light is synonymous with its energy. Add energy to light, you raise the frequency. High frequency light has more energy. This is part of why x-rays and gamma rays are so nasty: they have a lot of energy. They can break things when they pass through you.
So there’s an opening treatise on light. Where does building a theatre come in? Well, two things.
Firstly, as I described, I first performed the additive experiment in a dark theatre in high school.
Secondly, I’ve been playing with this ray-tracing app, and I thought using it would be a neat way to show you that long-past experiment.
However I’m at my self-imposed word limit, so I think I’ll put up a Sideband post to get into that. It would actually make a perfect Sideband.