Remember incandescent lights? They’ve largely been phased out because of their horrendously low efficiency—less than 5 percent. Incandescent bulbs are classified by how much electrical power they use, like 60 watts or 100 watts. But most of that power is turned into thermal energy, not light. Of course, if you’re trying to heat things up, like in the old Easy-Bake Oven, they’re great.
Fortunately there are alternatives. For a while, compact fluorescent bulbs were the main option, but buyers complained about their harsh effect. Today most people use LEDs. They’re far more efficient than traditional bulbs, and the light quality is better than CFLs—but not everyone’s a fan. President Trump, for one, says these newfangled lights make him look orange. Could he be right? Let’s find out.
Two Ways to Make Light
How about a quick refresher on how these different lights work? The incandescent is the simplest light you can make. Basically it’s a tungsten wire in a glass container. When you run an electrical current through the wire, it gets hot enough to glow. If the wire were exposed to air, it would burn and break—that’s why it’s sealed in a bulb. But that’s it. The problem is, because it makes light based on its temperature, most of the energy it uses is lost as heat.
Now for the LED, or light-emitting diode. (I often say “LED light,” which I admit is redundant.) These create light with a solid-state device. A semiconductor material contains an electron energy gap. When a current passes through this gap, it produces a particular wavelength—hence, a particular color—of light. That’s an oversimplification, but it’s fine for now.
But how do you make white light? There are two options. First, you could have three LEDs—a red, a green, and a blue. Combine these and you get white light (more on this below). Second, you could make an ultraviolet LED with a fluorescent coating. The UV light excites the electrons in the coating to produce many different colors of light. This is how old-fashioned fluorescent tubes work, except that the UV light is produced by LEDs instead of an excited gas.
To see how much better an LED is than a plain old incandescent, here are two pictures. The top one, taken with a normal camera, shows how much visible light each one emits—pretty similar. The bottom one is a thermal image taken with an infrared camera.
You can see that they yield about the same amount of light energy, but the incandescent (on the left) produces way more thermal energy. Yes, the LED gets warm too, in the circuit board that controls the voltage. But the incandescent is still much hotter. I also connected these bulbs to a power meter: The incandescent was using 63 watts, the LED only 6.5 watts.
Where Colors Come From
But what about color? Let’s start with some basic ideas. First, how do you see things? Really, there are two ways this can happen. You see the light bulb itself because some of the light it emits hits your eye. For most other things, light reflects off that object and the reflected light enters your eye. If there’s no light source, no light reflects into your eye and everything looks black. That’s what darkness is—the absence of light.
What about white light, like the light from the sun? It looks white because it’s a mixture of many colors. You can see these colors in a rainbow. Sunlight enters a spherical drop of water in such a way that different wavelengths of light (perceived as different colors by humans) bend by different amounts. Boom. You get a rainbow.
When we talk about this visible spectrum, we often break the colors into red, orange, yellow, green, blue, and violet. Really, there are an infinite number of hues between red and violet. But what’s cool is that, because of how our eyes work, every color we see can be produced using only red, green, and blue lights in varying proportions. As an example, combining red and blue light at equal intensities gives the color magenta.
Here is a great applet from PhET simulations that’s fun to play with. You can vary the intensity of the three lights to see what kind of colors they produce.
Yes, that’s a giant leaf. But I think it gets the point across. If you shine only red light onto this green leaf, nothing would be reflected. You would see the leaf as black. So, the kind of light that illuminates an object affects the color you perceive.
How Light Affect the Colors You See
OK, who’s ready for some data? Here’s what I’m going to do. I’m going to take this disk with several different colors on it: green, yellow, red, dark red, pink, blue, and light blue. It’s actually part of a physics experiment that shows how combining colors makes white (it spins).
Next I can just illuminate this with different lights and measure the apparent color. For the measurement, I’m going to use my phone. The camera essentially just collects light from an image with three different sensors (red, green, blue) and produces a digital value for each color—and that is the color of one pixel of the image. There are many ways to do this, but I used an app called ColorPicker. You just aim a crosshair over the color you want to measure (in the example below it’s on the dark blue part) and it gives the RGB values (between 0 and 255). Here’s what it looks like.
Now I can make a comparison of the apparent color for illumination from LED and incandescent lights. Here’s what I’m going to do—maybe it’s crazy. Since there are three values for each color reading, I can treat each reading as a 3D vector (with RGB values instead of x,y,z). If each color measurement is represented as a vector, then I can calculate the angular deviation from some standard measurement.
So, suppose that the measurement from the overhead lights is considered “standard.” (Yes, it probably would have been better to use natural sunlight, but I was inside at the time.) When I use the other lights, that vector color will be at a slightly different angle.
Here’s what I get. This is a plot of the angular deviation for the two lights (LED and incandescent) compared to the normal overhead lights.
What does this tell us? There’s not much difference between these two lights. Not much at all.
But what about a light that does make a difference? What if it was a green light? A red color patch would reflect only red light, so in this case it would appear black. Here’s what that same color wheel looks like with just a red, green, or blue light.
Yes, under green light, the red parts are indeed mostly black. They aren’t perfectly black because that’s not perfect red. Also, human eyes can trick us sometimes. When you put something next to another color, we don’t always perceive the actual color.
OK, but what about orange? How would a light make you look orange? The RGB values for the color orange are (255,165,0). That means you should have all the red, about half the green, and no blue. If you use a light without any blue in it, objects won’t reflect blue, and that will make things tend to be closer to orange (but not necessarily orangish).
So if you wanted to prevent an orange color, just use lots of blue. Incandescents aren’t really known for their excessive amounts of blue light. You know what can add extra blue light? Yup—adjustable-color LEDs. They make these things for videos and they’re pretty nice. You just turn a knob on the light and it changes colors. Try doing that with an dumb old incandescent.
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