Color temperature is used in everything from lighting, photography, and videography to manufacturing and astrophysics.
When white balancing your camera, printing a photograph, or trying to determine the surface temperature of a distant star, color temperature is a term that’s always thrown around. But what does color temperature mean? Is it hot to the touch? Or does it just want to have an argument or give you the cold shoulder?
All of the above, actually.
While there are many uses for color temperature, when it comes to film and video, color temperature refers to the characteristics of visible light and how it’s reproduced in your camera or display. Before we get to that, let’s get to some nerdy stuff first.
As defined by our good friend Wikipedia, color temperature “is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins.” Please bear with me if you hate word salad as much as I do.
The Kelvin Rating is named after the Belfast-born engineer and physicist William Thomson (later Baron Kelvin) and is denoted simply as K. It can be used to measure temperature all the way to absolute zero. That’s -273.15 degrees Celsius and -459.67 degrees Fahrenheit, which is super cold, mind you. When things get that cold, weird things start to happen.
But that’s a measurement of actual temperature. Kelvin can also be used as a measurement to denote the emission of thermal radiation (in the form of a hue from warm to cool). This, unfortunately, flips our visual understanding of hot and cold. We usually think of red as hotter and blue as cooler, but not here. For example, the light from an incandescent lamp falls around 3200 K and is perceived as a warm color, but the more thermal radiation something emits, its hue shifts towards blue. This is actually how metal workers judge the temperature of hot metals. Cool, right?
Check out the below color temperature chart for reference.
But when it comes to LEDs and fluorescent lamps, things start to get a bit more complicated since they emit light by a process different from thermal radiation. This brings us to correlated color temperature, or CCT, which is the color temperature that most closely matches human color perception. You’ve seen CCT denoted in the spec sheet of almost every LED and fluorescent light on the market, making this a great segue to…
Color Temperature in Film and Video
Regarding cameras and exhibition, creatives use color temperature to denote the mapping of color values to simulate ambient color temperature.
Modern digital cameras, both for photography and cinema, use the kelvin range to try and reproduce the color white by making the image warmer or cooler. This is called white balance and is used to match your sensor to either the cool color of daylight at 5500-6000 K or warm interior light around 3200 K.
Why do humans perceive indoor light as warmer? Because historically, interiors were light with either fire or incandescent bulbs, which come in around 3200 Kelvin. By shifting this "white point" (we'll see this again later) to a certain kelvin, the camera will perceive anything lower on the kelvin scale as warmer, while anything high will be seen as cooler.
Unless you’re shooting in RAW, it’s also important to set the correct white balance of your image since those parameters are baked in. While adjustments can be made in post, depending on your codec and compression, you can only push the image so far before it breaks down. This is one of several benefits when it comes to RAW workflows. Since the white balance is recorded separately as metadata, you can set it to whatever you want when doing color correction. However, creatives will always have to keep in mind the color temperature of their light sources.
The color temperature scale is also used the same way in exhibition, either with cinema projectors or displays. This is done by setting the target white point which is like white balance, but this term is used for displays. This term is defined as a set of color values that define the color white.
Most displays are either set to 6500 K (denoted as D65) or 5000 K (D50), but you can set whatever white point you need from 4500-9500 K. This shifts the image either warmer (more yellow) or cooler (more blue). Cinema projectors use a white point of D65 since films are usually shown in an (almost) pitch black space. But when it comes to displays outside, such as giant video walls for advertising, a white point of D50 can be used.
It’s also important to set the white point of your display when shooting in a volume since your camera will be recording the projected image. If your white point is off, the background will never match the light falling on your subject. While all of this is color temperature in a technical sense, the color temp scale can also be used creatively.
Taking Your Creative Temperature
By looking at how color temperature is used in cameras and lighting, we can start to use white balance and our CCT in a whole lot of creative ways.
For example, when shooting indoors, we can set our white balance to 3200 K to match our warm interior lights. But when we let in light from outside, it will appear blue in comparison since it measures at roughly 5500-6000 K.
The inverse is also true. By setting your white balance to match daylight, any incandescent lights will appear warmer. Lewis Potts gives us a great example below.
Why would we want this kind of creativity? Well, according to the Encyclopedia of Laser Physics and Technology (via Wikipedia) warmer lights are used to promote relaxation, while color lights can enhance concentration. Creatively, a warmer color temperature can be used to enhance the feeling of comfort or safety, while a cooler temp can be used to create tension or unease.
To go further, filmmakers can match the color temperature of their lights to create one unified look so that the lighting of an interior matches the exterior.
Okay, we have to come clean. We glossed over quite a bit. Color temperature for exhibition alone deserves its own article. But that’s some high-level technical stuff that most filmmakers won’t have to worry about (unless you’re making DCPs on the daily).
For everyday creatives and filmmakers, especially those on a budget, the basics of color temperature will be more than enough. With this quick overview, you should have all the technical knowledge you need to get the shot you want. You should also know how to bend the rules of color temperature for creative effect.
If you do want to dive a bit deeper, check out all of the creators we linked in the photo credits.
But before you run off to start futzing with your kelvins, remember that you must learn the rules before breaking them. Happy shooting, and let us know how you creatively utilize color temperature in the comments!
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