The incandescent color spectrum curve

There's a time and place for everything, including amber.

In the September 2011 issue I wrote a piece, “The Ethics of Color,” where I proposed a very specific approach to the use of color media in the theatre. Two concerns were brought up about this by readers (and myself upon a later read). First: The approach did not take into consideration the myriad lamp types we have beyond the ubiquitous HPL for Source 4. And second: The piece may have given the impression that amber is never a good choice. This is far from the case.

To better understand when it would be good idea to use amber, it’s important to understand the types of light that come from different lamps. Today we often find ourselves with numerous lamp types and color temperatures when we combine incandescent and HMI fixtures—not to mention moving lights and followspots with their HID sources, or fluorescents and LEDs and their spikes in color. It can be daunting trying to figure out how to make the “white” from each look alike. Still, a few basic principles can help us.

Lighting on a Curve
The HPL halogen lamp in a Source 4 is a variation of the incandescent bulb. A standard incandescent bulb produces a warm soft light. Its color spectrum curve is heavy in the reds and ambers, then follows a gentle slope down from 700 nanometers (red) to 400nm (violet). A halogen lamp (like the HPL in a Source 4) also produces a continuous spectrum (since it is a refined incandescent), but thanks to the way it’s built it operates at a higher temperature. This higher temperature allows more blue and violet into the mix and shifts the color spectrum, making the light appear cooler. Filters like R302 (a very pale amber) were developed to essentially shift a halogen lamp’s output to something closer to a true incandescent, weighting the spectrum closer to red again, and restoring warmth.

Now, if you have spent any amount of time working with Xenon followspots you know that getting them to blend smoothly with a rig full of Source 4’s can be a lot of work. Why is this? The spectrum curve for high-intensity discharge (HID) lamps (like a Xenon source) have spikes in the blue and green wavelengths. Because of these spikes, the “white” light coming out of the followspot washes out warmer tones in skin and clothing. In order to keep those warmer tones, you have to filter out the green and blue spikes—and this is exactly what an amber filter will do. A true amber filter will knock down some of those blue peaks, and shift your spectrum closer to amber. A bastard amber filter will lessen both the blue and green peaks, restoring warmth to skin, fabrics and paints. You may need something as saturated as L152 just to make the spotlight look white to begin balancing to the rest of your lights.

This choice of ambers points to another problem when dealing with lamps. Every lamp is different. And the color of an individual lamp changes over time. A wide range of amber and bastard amber gels at your disposal is critical for getting the balance right. Sometimes all you need is a little R302. Other times you might need three to four cuts of gel to tweak the color just right.

Automated fixtures make the process of mixing their HID sources with your traditional sources much simpler: You just roll the color wheels until you get it right. But anyone who has tried to match a system of moving lights to, say, a system of Source 4’s with color scrollers, knows that you will always have at least one or two lights that consistently need a little more magenta or just a touch less cyan. If you are doing a flashy rock opera such precision may not be so critical. After all, when you just crank the cyan and magenta to full to get that deep blue, the lamp color differences will not be so terrible. But if you are doing more subtle color work, perhaps a Rodgers and Hammerstein musical, you may find yourself struggling to get that subtle but heightened naturalism to balance smoothly and consistently across the stage.

HID Color Spectrum Curve

Spiking the LEDs
LEDs present a curious problem. A red LED is closer to R26 than L106—they have a touch of blue rather than a touch of yellow to their hue. Amber and blue are more or less complementary colors. Thus, to offset the cool blue light you mix in a little amber. We need amber LEDs in order to mix colors that are attractive to human skin tones.

In fact, LEDs and HID moving lights present the best case for the regular use of amber in a theatrical setting. Both of these device types have a base color that is too cold and blue for human skin in many applications. Sure, that dreary Lear is going to love the cold color palette—but not the musical comedy or sex farce. For these we want to warm things up.

One thing to remember about amber is that a little goes a long way. Even with a palette made up mostly of pale blues and cool lavenders for the bulk of the performer lighting cranked up near 100%, a touch of pale amber, or even clear incandescent, need only be turned up to 20% or 30% to have a great warming effect on the stage picture.

For me, the best use of amber is for those rich and powerful sunsets and sunrises. Sure, you might want purple and salmon in there as well, but that rich warm amber sun is like nothing else for telling us what time of day it is.

When considering a sunset—even if you key the scene with lavender or purple—you want a lot of amber out there on stage. You may go so bold as a G315 or a more sedate and rosy G310.  Whatever direction you go in, when lighting a sunset it is hard to be too saturated.

In direct contradiction to my last article suggesting one stay away from amber, especially when lighting faces, I’ll mention one of my favorite lighting effects. Key your sunset from a low balcony rail position—the lower the better—and color with a heavily saturated amber like R22. Then turn it on to full. The flatness of the light and the richness of the color speak volumes about when and where we are. We all recognize that low-to-the-horizon-sunlight pouring on us as if it were struggling to get every last lumen out before it hides below the horizon. This can be particularly powerful with slow musical moments like “Those Canaan Days.”