What do we really mean by ‘white’ light?
06 Apr 2015

What do we really mean by ‘white’ light?

Have you ever purchased light bulbs for your house or church, whether they be those spiraling little CFLs, a traditional halogen bulb, or the new fancy LEDs, only to get back home and find out that the “white” light bulb you purchased is actually a different color than everything else in the room? While all of these different lights are technically defined as “white light,” what you are actually seeing is a difference in color temperature. In industry terms, this is also known as CCT, which means “Correlated Color Temperature,” and is rated in degrees-Kelvin.

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When discussing the output of a lighting fixture, ‘CCT,’ should not be confused with actual ‘color.’ CCT refers specifically to white light, which contains a full spectrum of colors as perceived in a rainbow, or learned in your 8th grade science lesson about ROY-G-BIV. The colors of light we see are measured using the CRI, or “Color Rendering Index,” which is oriented (or centered) on the CCT of the white-light source. Basically, as the CCT shifts around on the spectrum, so does the CRI which it is based on. Due to this variable, someone decided that we should just use one standard for everything to make it easier, and the CRI index that we use to measure color output is based on a CCT, more or less, of 5,000 Kelvin. Follow that wiki link above if you want the fully detailed explanation, because it’s not actually as simple as I tried to explain it here. The point is, color and color temperature are two different things.

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Color Rendering Index (CRI) Chart

For the super technically-minded who like to know where this stuff comes from, this system of CCT measurement is derived from the theory of heating up a ‘black body‘ element until it glows a certain color. The lower temperatures burn at a ‘warmer’ color, which has a more orange or amber color, whereas higher temperatures burn at a ‘cooler’ color, which has a more blue-ish tint. (It can be slightly confusing, because the vernacular we use to describe “cool” versus “warm” color temps is actually opposite of how the physics apply to reach the desired state.) The same is true of nearly any combustible substance, and can be observed in every day occurrences. If you have a gas stove in your kitchen or a propane grill on your patio, take a look at the flame coming off the burner. Right where the gas comes out and is the hottest, you’ll notice the flame has a very bright blue color, and as the flame moves away from the burner and isn’t quite as hot, the flame turns to an orange color. Somewhere in the middle, you might see something that looks more like the color that we perceive as true white.

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So, all of the science-y stuff aside, there’s a really important discussion about how these principles apply to lighting used in our every day world. The shifts in CCT carry a bunch of different variables, and sometimes those variables are really important, while other times, they’re very negligible. Have you ever paid attention to how the lighting in a certain room might make you feel more sleepy, or how different light might make you feel more alert? That’s because the CCT of your room lights actually affect your brain receptors in ways that really make you feel that way. A low CCT (warm, amber color) can make you feel more comfortable and cozy–like sitting next to a warm fireplace. Whereas a high CCT (cool, blue colors) can keep you more alert and attentive. This is why you often find office and commercial spaces lit with CCTs that are neutral or cooler in nature, because they are less comfortable, and why warmer CCTs in your home feel more cozy. So, aside from how your brain interprets light and makes you feel, there are some technical implications as well.

Just like the human eye, the lens of a camera takes in light as it is reflected from various surfaces, and translates those wavelengths of light into the different colors we see. However, camera lenses aren’t as perfect as the human eye. They don’t see color quite the same, and therefore, the colors reproduced by the camera might be different than what our direct eyesight is seeing. When you consider that many churches use video capture to reproduce their service content, good lighting plays a big factor in what’s being seen. Sometimes, this looks vastly different than what you might see if you were sitting there in person. Movies and TV studios have the advantage of separating you from the actual content being captured. But, what happens when you’re sitting in church, and the image on screen makes your pastor look like an icy-cold Mr. Freeze, but you look directly at him and he looks like his normal fleshy self? It creates an awkward separation in what’s being perceived, and sometimes, that can be detrimental. So, what causes this, and how do we fix it?

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CCT Difference on Fleshtones (image via http://www.lacolorpros.com/)

 

In a building like a church, you have many different light sources that may be affecting the image your eyes and cameras see on stage. In traditional church buildings with lots of big open windows, you might have lots of natural sunlight coming in and washing the room in light. In more modern architecture, you might be dealing with much fewer, or possibly no windows at all. Either way, you also have the lights that are required to illuminate the room in general. You might have control over those lighting levels, or you might not. Additionally to all of this, you may or may not have lights that are specifically utilized to illuminate the stage and pulpit areas. The blend of lights from all of these different sources have created a scattered spectrum of light on your stage, and it becomes difficult to predict and to control what you are seeing live or on camera. Thankfully, there are some really smart folks out there that are trying to make this easier.

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Church Stage Lighting – Stage Lights at 4000K (direct), against midday sunlight (5000K+) coming in from left.

In traditional stage applications (before the use of LED technology), most users were confined to the use of halogen lights, which emit a low CCT of around 2,700K-3,200K. Sometimes, these lights created an undesired orange and amber tint on people’s skin-tones, and so companies like Lee and Rosco created filters or ‘gel‘ to correct the CCT output of the fixtures to achieve a more desirable CCT level that would allow the camera to “see” color more similarly to what your eyes see. For instance, if your halogen light had a CCT of 3200K, you could use a “1/4 CTB” to achieve an output CCT of 3500K that works better with a particular camera lens and sensor. (The abbreviation CTB means, “correct to blue” and CTO means, “Correct to Orange.”) This process permitted you to use a single correction filter (or a combination of filters) in your lights at any one time, and didn’t give much flexibility for being able to change variables easily. These days, however, with the use of LED technology, this process is becoming much simpler.

Some manufacturers are now making LED fixtures that utilize “Variable White,” or “Dynamic White,” technology. Typically, this involves using one set of very warm white LEDs and one set of very cool white LEDs all within the same fixture, and mixing the output from each set to achieve a blended CCT somewhere in the middle. This shift happens electronically, and can be controlled by any standard DMX controller. By doing this, we can now work more fluidly and dynamically than ever before. In a church with big open windows, we can now shift our stage lights to match the incoming sunlight at different times of day. In closed environments, we can now shift CCT to find a better balancing point that looks similar to the naked eye, as well as camera reproductions. We can also shift the ‘mood’ and comfort level of our stage appearance by changing the CCT output of our white light.

This post is not meant to convince anyone that owning LEDs that can shift your CCT is the correct solution for everyone. As with most of our posts, this is meant to provide useful information that assists the dialog in determining what might be the best solution for you and your needs. To discuss how this information might be useful and applicable to you, please feel free to get in touch and we’re happy to talk through the options with you.

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Color Temperature Spectrum Chart with References (Image via http://www.seesmartled.com/)


Justin

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