Have you ever wondered why we often have so many lights when we go on a video shoot? Or how we’re able to make an interview appear to have natural light when it was shot in an interior room? You might be surprised to know that a lot more goes into lighting a video than just plugging in a light and turning it on. Eric Andrews has the answers, but first, he needs to explain the expanding universe to you.
Have you ever wondered what color temperature is and how it’s different from color tint? Maybe you studied color temperature in school, and you learned that tungsten is red, and daylight is blue, and maybe you even learned the Kelvin scale. But, if white light is supposed to be made up of all the colors of the spectrum, then why is it that red and blue are the only colors we ever talk about? What about green or purple? I would love to explain to you what I’ve learned about color temperature and color tint, but first, I have to explain to you the expanding universe.
The Expanding Universe
I’m no scientist, but sometimes I look up at the stars. And when I look up at them, sometimes I notice they look slightly red, or green, or blue. Because the light from those stars can reach our planet, scientists can do what’s called a spectral analysis of that light. Now, that’s really as simple as it sounds. It’s just an analysis of the spectrum of the light. Now, a spectral analysis can be done on things that don’t produce light, but only reflect it, like hydrogen or helium. A real scientist could compare the spectral analysis of the light of the star saying, “Look, that star is made of hydrogen, or helium, or Kryptonite.” That’s how we know what the planets and stuff are made of.
Let’s Talk Doppler Effect
So, how do we know that the universe is expanding? It’s because of the Doppler effect. You’ve observed the Doppler effect before when you’ve heard an ambulance or a fire truck drive by. The sound waves leave a siren at a constant rate. But if that ambulance is moving towards a static observer, the sound waves start to stack on top of each other. When it moves away, it starts to spread out. This causes a change in the way we perceive the sound being higher or lower. The Doppler effect applies to light the same way it applies to sound.
A scientist could do a spectral analysis of a body in space and say, “Wow, this looks like it has Kryptonite in it!” But, the markings that indicate Kryptonite look slightly redder than we would expect. So, what does this mean? If a body in space is moving away from us, because of the Doppler effect, its light waves would spread apart and its spectral analysis would have a red shift. If the body were moving closer to us, the light waves would stack on top of each other, and we would observe a blue shift. Knowing this, we’ve observed the furthest-most galaxies of the universe, and now we know it’s expanding.
When you’re thinking about the relationship between color temperature and color tint, it can seem kinda menacing. This is the way I think of it. If you can do a spectral analysis of a body in space to understand the expanding universe, then you can do a spectral analysis of any light source: a tungsten bulb, a fluorescent bulb. I’m not really interested in knowing what individual atoms those things are made of, but I am interested in knowing how much radiation a light source gives off at a given frequency, what colors it’s made of. A tungsten bulb has a smooth transition between colors and favors the warmer hues. While daylight, which is just diffused light from the sky, also has a smooth transition, it favors the blue hues.
Understanding Color Hues and Color Tint
Now we know that white light is just all the colors of the spectrum balanced equally, so when you’re white-balancing, all you’re doing is saying, “Hey camera, my light source has a lot of blue in it, not much red. So can you shift it more towards the red, instead of the blue so it looks more neutral?”
This is the basis of color temperature, but what the heck is tint? It’d be way too easy if our only light sources were daylight or incandescent bulbs. Instead, we had the brilliant (terrible) idea of making fluorescent bulbs, which spike up in the greens and the yellows.
Well, every light source has a different spectral power distribution with different amounts of each color. So, unless you’re using all daylight or all identical tungsten bulbs to light a scene, in my opinion, you’re using mixed lighting because no camera can compensate for a wild spectral analysis.
A Real Life Example
Let’s say you’re shooting an interview with a Canon C100, and you’re lighting with Kino Flo, so you have an option of either daylight or tungsten bulbs, and this exact location is the only background that looks good. You have a very large window spilling in daylight, and there are overhead tungsten lights that you have no control over. You’re going to have mixed lighting no matter what, so what should your white balance and your fill light be set to?
So, if the overheads look all right on the background and the window light is kinda being used as a back light, it might make sense to fill with daylight so the subject key light would match. However, the overhead light is casting warmer highlights all over the subject.
When we switch the white balance to tungsten, obviously the subject and the light hitting the wall from the window is going to look blue.
By then filling with tungsten, the warmer highlights are matched in color temperature and are less noticeable.
Today, we learned about the spectral analysis of light waves and how the Doppler effect shows a red shift in the outermost galaxies of the universe, proving its expansion. We also learned about how spectral power distribution curves indicate the color output of a light source, and the act of white balancing is just an attempt to flatten the spectral distribution curve of that light. If you want to learn more about color temperature or the expanding universe, I would Google any of these words, because that’s what I do.