Introduction to Color Temperature

The way we perceive color is greatly influenced by our cultural understanding. We all grew up learning that Fire is Hot and Ice is Cold. Therefor red and orange are warm colors while blue and cyan are cool colors.

This association in our mind is so strong that filmmakers can actually invoke a sense of temperature just by the color palette they use in their films.

Take for example Spike Lee’s 1989 film “Do the Right Thing”

The film beautifully photographed by Ernest Dickerson, is awash in yellows, oranges and reds invoking the heat of a long, hot day in the Bed Stuy (Bed sty) neighborhood of Brooklyn New York The urban cityscape is a vibrant community full of life – a diverse neighborhood where every one knows and accepts each other. But things are boiling up under the surface. Old hurts are being remembered. Tensions build like a pressure cooker. And things are about to explode.

Contrast it to the Coen Brothers’ 1996 film Fargo

Photographed by Roger Deakins, Fargo is dominated by blue and grey – even the white snowy exteriors cast cold bluish light so that weather itself mirrors William Macy’s character’s icy soul. Its constant reminder of the frozen landscape surrounding him and his inept henchmen.

Both these films utilize production design to accentuate hot and cold, but they also push the feeling of temperature using creative applications of white balance and color temperature.

What is Color Temperature?

When we talk about color temperature, we’re talking about the property of white light. White light is really a creation of our own minds – there’s no color white in the light spectrum. The color White confounded people for thousands of years. It took Isaac Newton in late 17th century finally demonstrated using a prism that white light was really a mixture of all other colors of light.

But precisely defining the proportion of different colors and tying that to temperature would have to wait till 1900 and Planck’s law.

Max Planck was a German physicist commissioned by German manufacturers to figure out the best temperature to heat the filament of light bulbs for maximum light and minimum electricity.

He tried to tackle the problem with contemporary theories but the equations just weren’t matching up with hits experimental data. That’s when he put forth what would later become Planck’s law which described the type of electromagnetic radiation generated by a theoretical black body at a given temperatures.

Let’s back up… You see, everything in the universe that has a temperature above absolute zero gives off some sort of electromagnetic radiation whether that’s infrared, visible light, ultra violet or x rays and everything between…. Even you and I give off radiation but it’s in the form of low energy infrared which we commonly call heat – that’s what IR Night Vision Goggles pick up.

As you increase the temperature of something, it will give off more and more heat or electromagnetic radiation, get it hot enough, it will start to glow – now it’s giving off radiation in the form of visible light. Continue raising the temperature, and it the glow will go through a very specific range of color which is mathematically described by Planck’s law.

This is what we mean when we talk about color temperature – its the color of white that would correlate with the color of light a theoretical black body at that particular temperature.

What was the temperature that Max Planck finally settled on as the ideal for light bulb. It was 3200K which is still with us today in the form of incandescent light. In the filmmaking world This number is also known as tungsten balanced.

The Sun’s surface temperature is around 5800K but Sunlight after being filtered through our atmosphere can range anywhere from a correlated 2800K at magic hour (sunrise/sunset) and even up to 6500k on an overcast day. For most applications 5600K, color of light on a clear midday, is what we mean by daylight balanced

These are two examples of light being created by hot objects where really the light is more of a by-product. How do you get lighting for film without all the heat?

The first alternative are fluorescent ights which uses a tube filled with mercury vapor and an inert gas. When electricity is passed through, alternating very quickly, the gas becomes a plasma and gives off UV radiation. The UV radiation strikes the walls of the tube which are coated in phosphors and the tube begins to fluoresce and give off light. So instead of heat, it’s the glow of the excited phosphors and the mercury gas that’s generating light.

But unlike an incandescent bulb that gives off light in all frequencies according to Planck’s law Fluorescent bulbs tend to spike only at certain frequencies, mainly at the primary colors Red, Green and Blue. Red and Blue are colors created by the phosphors in the tube and green is created by the light emission of mercury. For cheaper bulbs, manufacturers will sometimes increase the amount of green because it gives the bulb a brighter appearance being that green is right in the middle of the visible spectrum. Unfortunately this can give footage shot under cheap fluorescent lighting a green tinge.

For photography and cinematography uses, manufactures mix different chemicals into the phosphors to get a fuller spectrum of colors as well as to alter the correlated color temperature so you can get tungsten balanced and daylight balanced fluorescent bulb. To get a more full spectrum, look for bulbs that have a higher Color Rendering Index or CRI. A CRI of 100 is full spectrum like the sun- for the best results use bulbs rated 90 or higher.

LED lighting is the newest alternative to incandescent lighting but they also can present many of the same issues as Flourscent lights when it comes to limited spectrum. The color of an LED is based on material used in the diode of the Light Emiting diode. There are several ways to get white light, either by using phosphors or by blending different colored LEDs together in a single fixture. Some fixtues even have the ability to dial in your color temperature by mixing the intensity of different colored LEDs.

Color Temperature in Production

There are traditionally two important numbers you should know by heart: 3200K which is the temperature of tungsten lighting and 5600K which is the temperature of sunlight at midday.

Almost all cameras have the ability to set a custom white balance using a grey card or white card. This is done by filling the frame with something gray or white and pressing the white balance button which zeroes the values so that color neutral.

For much better control, professional cameras also have the ability to dial in a specific number for your white balance. This is great for dialing in your look – if you want more of a warmer tone, push the color temperature higher, more cool, push the temperature lower.

And If you’re shooting with a camera that shoots in RAW format, you can save your white balance decisions until post.

A common color temperature problem that pops up is when you have competing light sources with different color temperatures – like you’re shooting indoors near a window and using tungsten light.

 

If you white balance to 5600K, the indoor lights will look orange. If you balance to 3200K, the light from the window will look blue. To get them to match you can use gels – either cover the entire window with CTO (orange) gel or just cover the light with CTB gel.

Corrected with CTB on light and camera set to 5600K

Of course there’s no reason why you can’t use that disparity for artistic effect.

It’s also worth mentioning here that the dimming of tungsten lights will lower their color temperature and make them look warmer. After all, the filament isn’t getting the same current therefore it’s not burning as hotly so by Planck’s law, they will be a lower color temperature.

Now there’s no need to adhere rigidly to any of these numbers. Just because we’re shooting under tungsten lighting doesn’t mean we have to set the camera to 3200K. Or that we can’t blend different color temperatures in a single shot and mix cold outdoor light with warm interior light. But understanding the mechanism of color temperature will help you solve artistic challenges when you’re on set. These tools go way back – from our earliest moments huddled around a warm life giving camp fire to Isaac Newton messing around with pieces of glass to Max Planck trying to figure how hot a light bulb should burn and founding the basic tenets of quantum mechanics in the process: each step furthers our understand and history – so use it and make something great.

 


Quizzes

Intro to Color Temperature Quiz