Mixing Color for Theatrical Lighting

WHEN WORKING ON A PRODUCTION, a lighting designer relies on many tools to create the look and feel of a show. Most of them are based on the qualities or characteristics of light they can control. These include intensity (how bright or dim the light is), directionality (where the light is coming from), and the subject of this article ― color. Color, both in light and in pigment, is all around us, yet we don’t always take time to analyze it and think about how it affects our mood, intentions, or focus. Designers will use light to affect all of these factors as they work with the rest of the creative team to tell a story.

To look at color, we need to analyze its building blocks. Many of us learn the primary colors in elementary school, but it is important to distinguish between primary colors of pigment (paints, dyes, or inks) and primary colors of light. The primary colors of pigment are red, blue, and yellow. With these three colors of paint, it is possible (in theory) to create every color you would ever need. The secondary colors are a result of mixing the primary colors: red and blue make purple; yellow and red make orange; and blue and yellow make green.

The primary colors of light are red, blue, and green. This presents new challenges (where does yellow come from, for example), and it requires us to learn a new set of secondary colors created when we mix two primary colored light sources. Red and blue create magenta; blue and green create cyan; and red and green create yellow. While it may seem counterintuitive to think of mixing two colors to create yellow, you can see this more clearly if you imagine the full color wheel and try to determine where yellow would fall.

Two more distinctions between light and pigment deal with the combination of complementary colors and the combination of all three primaries. In pigment, combining complementary colors ― those across from each other on the color wheel, such as red and green ― produces black. Furthermore, if you mix all three primary colors of pigment together, you also get black. In lighting, the addition of two complementary colors ― blue and yellow for instance ― will produce white. The same thing happens when all three primary colors are combined in equal measure: The result is white light.

HOW DO OBJECTS HAVE COLOR?

When we look at a green piece of candy under normal “white” lighting, why does it look green? To our eyes, an object appears to have color based on the portion of visible light it reflects. “White light,” or full-spectrum lighting, is the collection of all the wavelengths of the electromagnetic spectrum that we can detect with our eyes. Each of these wavelengths, or each portion of the spectrum, correlates to certain colors the human eye perceives. Thus, our green piece of candy only reflects the portion of visible light our eyes consider green. In the same manner, a red piece of candy only reflects the visible portion of light our eye considers red.

What would happen if you were to shine only blue light on these two pieces of candy? Because the green piece only reflects green light, and the red piece only reflects red light, both pieces of candy would reflect nothing back to the eye. This absence of color is what we perceive as black, and both pieces of candy would look nearly identical.

MIXING LIGHT COLORS

It is easy to talk about mixing colors of paint, but how do we talk about mixing colors of light? In light, there are two main types of color mixing ― additive and subtractive. To discuss them simply, let us imagine we are lighting a plain white projection screen, as a white object reflects all visible light back to the viewer.

Additive color mixing
In additive color mixing, two sources of different colors are projected onto our white projection screen. Both colors are fully reflected to the viewer, and the brain perceives the two colors and creates the mixture. This process is called additive color mixing because we are adding two colors on top of each other to create a new color. For instance, we could shine separate red lights and blue lights onto our screen, and our brain would interpret this as magenta. If we vary the intensity (brightness) of the blue and red lights, the brain starts to move along the color wheel toward red or blue. More red light than blue light would give us a pinker color; more blue light than red light would give us a more purple color.

Additive color mixing is common in cyclorama and backdrop lighting. Using red, blue, and green sources, a designer can mix nearly any color they like on the backdrop. We also see the use of additive color mixing in one of the most common lighting devices we interact with ― the screens on our phones, computers, or televisions. Generally, these screens are built of millions of individual pixels. Each pixel contains a red, green, and blue source, and they emit light at varying intensities to create the millions of colors we see. As LED lighting fixtures become more common in theatre, we see another example of additive color mixing. Many LEDs are RGB fixtures (composed of red, green, and blue sources) that use additive color mixing to produce their range of colors. Often, additional colored LEDs such as amber (RGBA) or white (RGBW) are included with the red, green, and blue sources to provide more options.

Subtractive color mixing
Whereas additive color mixing uses multiple colored sources to create new colors, subtractive color mixing commonly begins with a full spectrum source and removes portions of the visible light spectrum to alter the color of the light. Imagine a theatrical lighting instrument pointed at our white screen. It produces a full spectrum of light, and the screen appears white. We then add a blue “gel” to the light and our screen appears blue. This is the most common example of subtractive color mixing in theatre. Gels, so called because they were originally made of gelatin (though now made of plastic), are colored filters placed in front of a white light to alter its color. As the name “filter” implies, the material only allows certain wavelengths of light through and blocks the rest, converting them mainly into heat. By removing or subtracting part of the color spectrum, our eyes perceive a different color from white.

In our example, a light blue gel filters out just a little bit of yellow light, the complement of blue. A dark or “saturated” blue gel would filter out nearly all the spectrum that does not correspond to the color blue, blocking all green and red light to leave only blue light.

Subtractive color mixing is also how most non-LED moving lights (and some LED moving lights that use a white source) produce their color range. Using filters of the secondary colors (cyan, magenta, and yellow) in various combinations, they produce the full array of colors through subtractive color mixing. In the example below, a cyan filter prevents red light from passing through (as cyan is the complement of red), and magenta prevents green light from passing through. By combining the cyan and magenta filters, you produce only blue light, as all red and green light is stopped by the filters. Interestingly, if you combine all three secondary colors using subtractive color mixing, you will have blocked nearly all of the light ― essentially mixing the three secondaries to produce black.

Knowing how color works in light, and specifically how colored light is mixed, is the first step to understanding how to use color in your lighting design. The next step is putting that knowledge to work to set the mood and environment, bring out the best in scenery and costumes, and work with the director and other designers to tell the story of the play.