WHITE BALANCE AND COLOR TEMPERATURE
As we discussed in the exposure article, a camera’s purpose is to “capture” (read and interpret) light. And light - in its most practical, simple sense - is defined by its intensity and color. The intensity of light most directly affects exposure, and by extension brightness, of the image; whereas the color of the light affects… the color of the image. Sounds simple, eh? For the most part, it is, but there is more to it. In exposure, you ration the light to determine what portions of the image fall into the shadows, highlights, etc. With color, you set the white balance to determine a context for whether the camera sees a light source as warm, cool, neutral, or something else entirely.
What is White Balance?
White Balance determines how your camera interprets colors, with an emphasis on the color white as a reference; since we all know what a neutral, true white should look like. While grey and black are both neutral colors as well, it’s not as easy to determine shifts in color, compared to white.
A neutral white balance means that your camera settings are in line with the lighting conditions to make the color white appear true and neutral (along with all other colors in that lighting condition). Any other white balance might make white appear warmer or cooler, or even make it take on a different color altogether, such as green or magenta. As mentioned above, it’s not just the color white that is affected, but all of the colors in the image.
Many people treat ‘White Balance’ and ‘Color Temperature’ as if they were synonymous, but White Balance is actually a term that refers to BOTH Color Temperature and Tint; so Color Temperature is a defining trait within the larger concept of White Balance.
Color Temperature is a measurement of the warmth of light. The unit of measurement of Color Temperature is the Kelvin. The Kelvin Scale goes from 1,000K (one thousand kelvins) to 10,000K (ten thousand kelvins). The lower the kelvin value, the warmer the light source is, and vice versa.
When it comes to film and video, there are a few important stops along the Kelvin Scale.
The first is around 5600K, which is the approximate color temperature of daylight, or direct sunlight. While it might seem strange, daylight is actually rather cool (blue) in color, compared to most other light sources. The vast majority of film stock is daylight balanced. So to achieve a (close to) neutral white color while shooting in daylight, set your camera’s color temperature to 5600K. And since the moon is a neutral grey color, moonlight is around 5600K as well (although it’s not very practical to try to shoot video under moonlight).
Note: During ‘Golden Hour’ the color temperature of the sun’s light falls drastically toward tungsten range - hence, the warm, golden light. The constantly changing color temperature, in addition to the plummeting light levels, make the Golden Hour a frustrating time to shoot any sort of sequence or fiction, so plan accordingly.
The second is around 3200K, which is the approximate color temperature of incandescent light bulbs and tungsten production lights. These lights, compared to daylight, are very warm in appearance, yellow to orange. Up until very recently, the average household was filled with incandescent light bulbs, which typically have a color temperature in the 2500K-3200K range. The incandescent light bulb shares many traits with the tungsten light. When using lights to illuminate a scene, filmmakers historically needed lights that were bright enough to adequately expose low ISO film at relatively small apertures, and the only kind of light that could practically do this were tungsten lights, and so tungsten-balanced film was invented to achieve a neutral white balance when using tungsten lights.
There is a third stop in the 4400K range, which is the approximate color temperature of fluorescent lights, which are still commonly used in many classrooms and businesses. These fall right between daylight and tungsten on the Kelvin scale, and as such are either warm or cool, depending on your point of context.
Tint is any additional color affecting an image, other than the warmth differences of color temperature. The most common example of this in film and video is the extra tint put off by fluorescent lights. As mentioned, fluorescents have a color temperature of around 4400K, which is right between warm tungsten light and cool daylight. In addition to that trait, though, fluorescents also typically cast a green tint on subjects.
Due to this being the most common tint color, some cameras only offer tint adjustments along a green-magenta scale. Others, however, allow you to add or offset tint of any color.
Color Temperature: Camera setting vs Light Sources
A very important concept to understand when trying to master white balance is that your camera settings are really just setting a point of context for what sources of light will appear warm, cool, green, etc.
Daylight, around 5600K, is a cool light source, but setting your color temperature to 5600K will give you a neutral white image. Any other light sources in the frame that have a higher Kelvin value than your specified color temperature will appear cooler, while light sources that have a lower Kelvin value will appear warmer. This is always true, no matter what your color temperature setting is.
We can even make daylight appear warm, and tungsten lights appear cool! All we need to do is set our color temperature to a higher value than the light source to make it appear warm, and to a lower value to make it appear cool. Since daylight is around 5600K, we could set our color temperature to 7000K, for example, to make the daylight appear to be a warmer source. Likewise, setting our color temperature to 2000K or so would make incandescent and tungsten lights appear cool.
It’s possible for some parts of your image to be warm, and other parts to be cool. That happens when your image is lit by more than one light source, and the sources have different color temperatures. This is called ‘Mixing Light.’
The most common occurrence of this is one that you should try to avoid: Filming subjects inside, lit by incandescent or tungsten lights, near a window where substantial amounts of daylight are making it into your frame. The color temperature differences here are 2400K or more, which is too strong of a difference to look good in almost any use, short of a very good colorist doctoring your image.
Other instances of mixing light can be desirable or beneficial, however. A frame that has some warm light and some cool light will have what’s called ‘Color Contrast.’ This is when opposite or complementary colors create a visual contrast in the image without necessitating a variance in luminance. This is a helpful trick when trying to create visual contrast in your image without sacrificing details to highlights and shadows.
Keep in mind the contextual nature of color temperature, which applies when mixing light, too. If you set your color temperature to the coolest light source, then that source will appear neutral while all the others will appear warm. Likewise, if you set your color temperature for the warmest source, that source will appear neutral and all of the other sources will appear cool. You can also, of course, split the difference so that some sources appear warm while others appear cool. Where you split the difference in color temperature will affect the warm-cool balance of the image.