What is Kelvin temperature and why should you care? When used in photography, Kelvin temperature is a scale that measures the relative warmth or coolness in a given scene: how yellow/red or green/blue, for instance, the light is that you’re shooting in.
Wikipedia will quickly put you to sleep with its definition about the Kelvin unit and Baron Kelvin:
“The kelvin (symbol: K) is a unit increment of temperature and is one of the seven SI base units. The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero, the theoretical absence of all thermal energy, is zero (0 K). The Kelvin scale and the kelvin are named after the British physicist and engineer William Thomson, 1st Baron Kelvin (1824-1907), who wrote of the need for an “absolute thermometric scale”. Unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to as a “degree”, nor is it typeset with a degree symbol; that is, it is written K and not °K.”
(Wait! Don’t click off this post just yet! I promise this will be relevant to your shooting!)
All you need to know is that Kelvin temperature, or color temperature, as we’ll refer to it as well, is an integral part of all of our shooting, and something that we can use to our advantage when we understand it.
Here’s a visual representation of the Kelvin temperature scale. Notice how lower temperatures are very warm, and following the color spectrum, increase in numeric value as they become cooler. So a sunset scene might show up on this scale as 1000-2000 K, while a cloudy day comes in at 7000 K. Interestingly to me, look at how open shade/skylight-type lighting taps out so much bluer at a full 10,000 K.
What’s the value to understanding this esoteric information? Well, I think one of our goals as photographers should be to understand what we are working with: namely, light, in all its complexities and beauty. Because our eyes and brains do such an amazing job of compensating for the differences in color temperatures that we encounter each day, I think it’s valuable to really intuit what the lighting is to our cameras, not just our brains. This can really help you become more truly aware of the light around you and how to control it.
An example: shooting after dusk, things look just muddy and gray to our eyes. But to your camera (and its color temperature scale), this light is very, very blue. Use this fact of color temperature to your advantage! This is my favorite time of day to shoot inside/outside shots. Usually there’s about 20 minutes or so of this special magical light, so you must prepare and plan ahead for your shooting agenda. This is when those great photos get taken of warm, glowing interiors with just enough exterior detail in the gathering bluish gloom to make everything look romantic and cozy.
Now look back at the Kelvin scale above. Note how 5500 Kelvin is what’s known as “high noon daylight.” This is important! Back when we all shot color film, this was the color temperature that the film was manufactured for: high noon daylight. How much of your shooting is done in ugly midday light? Not much of mine, but that’s the temperature of the ‘Daylight’ setting on your camera. If you take a look at the rest of the white balance settings on your camera, you’ll see other points on the Kelvin scale: tungsten bulb (3200K), cloudy day (7000K), open shade (10000K). What good does this do you? I usually like people in my photos to have some warmth to their skin tones, so I’ll bump this scale up: if it’s cloudy, I’ll put my camera on the “Open shade” setting (on my Canon, it’s a photo of a shady side of a house). The camera will then compensate, thinking the light is really bluer than it is, resulting in a warmer overall color cast to the photograph. You can do this in the opposite direction too.
Finally, another place that color temperature and Baron Kelvin affect us all: our computer screens! We all know how important it is to have a neutral computer screen to view our images on. But have you spent any time adjusting the color temperature of that screen?
Monitor calibration devices, like the Pantone huey and Xrite’s i1Display2 will make sure your monitor is delivering accurate color, but this costs money. So before you open up your wallets, go to the hardware settings for your monitor and check to see what default choices are available. Most monitors will have at least a few to choose from. You want to use the one in the 5500-6500K temperature range. This will most closely approximate a neutral, “high noon daylight” setting. Later you may opt for a monitor calibration device, but in the meantime, at least, use the proper default setting.
Hi, I’m Andrew Boyd, a.k.a. The Discerning Photographer, and I hope this post has been interesting and informative. Please leave me a comment about it, let me know what you’d like to see more of on the site! You can also sign up for email delivery of all future articles or my RSS feed. Thanks!–DiscerningPhotog