The World of Color

in Feeding the Machines

We are fortunate that we live in a world filled with millions of different hues, shades and variations of color.  Lighting engineers have provided us with the ability to adjust the wavelength of light coming from automated lighting fixtures so that we can create a multitude of colors on stage.  Lighting programmers are always working with color, and the consoles we program on a daily basis continue to provide us with more and more abilities to adjust the color outputting from our lighting instruments.  Early automated fixtures simply provided a fixed color wheel with twelve or so colors to choose from.  Today, most fixtures include very sophisticated color mixing system as well as fixed and special effect color adjustments.  It is up to the programmer to understand the color mixing processes that fixtures and consoles employ so that they can create the looks desired by the designer or production.

» Color Mixing Basics
Most automated lighting fixtures utilize a subtractive color mixing system.  In this system, the light source is white (or close to it) and contains most of the visible wavelengths of light.  Then filters (usually dichroic) are used to remove certain wavelengths of light, resulting a specific color output from the fixture.  For instance, if you bring in the cyan filter, the light will change from white to cyan.  The glass put in front of the path of the output has filtered out much of the red wavelengths to create a cyan color.  However, instead of just being a solid color on the glass, the fixture will use a pattern that slowly increases the saturation of cyan as it is adjusted into the beam.  This is what allows for color mixing, and by combining different variants of filters, you can easily create millions of different hues from a single fixture.   The most common color mixing parameters produce cyan, magenta, and yellow output.  Just remember that you are filtering light out as you mix, so if you bring in the cyan, magenta, and yellow flags, you should get a color close to black (very little or no light output).
The opposite of subtractive color mixing is (you guessed it) additive color mixing.  Here the process is reversed, as the light source actually contains several different colored sources that, when combined, together create a white (or close to it) color.  This is very commonly used with LED fixtures, but there are automated fixtures that use this principle as well.  Here you typically have a red, green and blue source, each with its own intensity control.  If you turn on the green output, you will get only green wavelengths of light from the fixture.  If you then add in the blue output, you will create a cyan color.  Finally, if you add in the red, you will see a white color.  The exact color of white that is created depends on the wavelengths of the individual colors (many RGB fixtures have a white that appears lavender).
» Working in Space
An automated lighting programmer must understand how different fixtures mix their colors.  If you are working with subtractive fixtures, then you will typically be mixing cyan, magenta and yellow, and with additive, you are mixing red, green and blue.  So how do you make both fixture types mix to the exact same “surprise pink” color?  In many cases, you may just have to adjust the CMY fixtures first, then do the same with the RGB fixtures.  However, most consoles now provide sophisticated “color space” controls. Instead of working with direct controls of parameters, they allow you to work within a combined color space where all fixtures operate the same manner on the console.  All fixtures will then have the same controls available to you, and the console will determine the correct DMX channels to adjust.
Typically, the lighting console will provide you with several color spaces to choose from, such as CMY, RGB, and HSI.  If you select the CMY mode, then all color mixing fixtures will operate as if they had CMY parameters.  This means you can now select both additive and subtractive fixtures and adjust the cyan channel to make the same modification to all fixtures.  Then, if you desire, you can switch to RGB mode and adjust the red parameter in the same manner.  Regardless of the mode you select, the console will continually work out the math for you to ensure that all fixtures appear to operate in the same manner.  Most consoles will even invert the default output (white or black) accordingly as you switch modes.  
» A Hue for You
As indicated above, another color mixing method is HSI (Hue, Saturation, Intensity).  In this model of color mixing you have parameters that directly adjust the color output instead of controlling filtering parameters.  With this method, you select a hue (the color you wish to output) and then adjust the saturation level.  No saturation will yield white output, a little saturation a pastel color, and full saturation a deep color.  The intensity parameter adjusts the total level of the output.  Some LED and digital fixtures directly provide an HSI color mixing mode, but you are more likely to find HSI as an option on your console.
» You Pick It
Many lighting consoles also offer graphical representations to aid you in your color mixing abilities.  The graphical representation can change as you change color spaces, or there may be only one color picker to select from.  In either case, the principle is the same.  A graphical chart (usually a pie chart or horizontal spectrum chart) is displayed.  You can then click or touch on the exact color you desire, and the fixtures will adjust accordingly to mix to a color close to what you have selected.  These can be fun to operate by just dragging your finger around the screen and watching your rig change colors.  They are also helpful when programming offline or in blind, as you can directly see the color you are selecting.  Of course, you are limited by differences of the graphic, the monitor and the fixture’s actual abilities, but generally it does get you close enough.
» Mixing and Matching
Every automated lighting fixture manufacturer selects the wavelengths their color mixing system will produce, and therefore it can be difficult to get different fixture types to match when color mixing.  Some manufacturers will use more saturated colors than others.  Their lights may appear brighter as you color mix, but you might have trouble getting deep reds and greens. Unfortunately, your console cannot help you with these physical limitations, but sometimes there are offsets you can adjust in the desk.  In addition, with the use of palettes or presets, you can store different values for different fixtures in the same location.  This lets you then simply select your “purple” palette and feel comfortable that all the fixtures will go to the same purple color (assuming you made them all match when you created the palette).
» Go Forth and Color
Color mixing lighting fixtures are tremendously fun to work with as you truly get to exercise your creativity.  It is important for you to understand the different methods of color mixing and the color tools available to you on your console.  In addition to CMY, RGB and HIS, there are several other color mixing methods that are sometimes utilized in lighting fixtures.  The next time you are programming a show, take a moment to think about how you are mixing colors and look for additional methods to improve your color choices.  You may just find something new and exciting.