Understanding Color Temperature
(Excerpt taken from my film book, “Shooting Better Movies: The Student Filmmakers' Guide.” Available on Amazon. See end of post for link)
I’m going to try and make this as simple as I can, as this is a big, tough subject! But knowing the basics of color temperature can definitely help you make better pictures. If you’re new to this, it does take a while to understand this topic. But you have to read, then try things out, read again, try again, and eventually you’ll get it. Trust me . . .
Imagine we have a black, solid metal object. When this solid is slowly heated, it will glow a certain color when it gets to a particular temperature. These temperatures are measured in degrees Kelvin (K). So we have a scale of various environments and sources that all give off different temperatures and therefore colors of light. For example, sunrises are orange, and night time has a blueish tint.
Our eyes can make adjustments for these differences, but the camera needs to be told what it’s looking at. If it’s wrong, it will produce a color cast over your image, which I’m sure we’ve all seen before when things might look a little blue or orange. The thing to first understand is the color and the temperature work in opposition to one another. Although we normally think of hot being red and cool being blue, on a color temperature scale, something getting hotter glows blue and something cooling down turns to more of a red. Take a look at the color temperature scale below.
As you can see, we have candlelight at 1800K, sunrise / sunset at 2000K, early morning at 4000K, average daylight sun at 5600K, and average shade at 9000K.
If the source of the light you are using is higher on the scale than what the camera is set to, you’ll get a blue color cast on your image or from that source. If the source is lower than the camera setting, you’ll get an orange color cast. We’ll figure out how we can use this scale when shooting in a moment.
Cameras normally have various settings for color temperature — also known as the “white balance.” It’s called “white balance” because you are telling the camera what white is. Our eyes adjust or balance naturally and see white as white in any situation, but the camera needs to be told what it is filming. So the four settings you might find on your camera are:
Daylight preset — measured at 5600K
Tungsten preset — measured at 3200K
Fluorescent preset — measured at 4300K
Manually set through balancing to white card or dial
As daylight and tungsten are the main two situations that you’ll find yourself shooting in, you can select each one via the presets. The manual function allows you to tell the camera the exact color of white it is seeing by placing a white card in front of the camera and holding down the white balance (WB) button for roughly 3 seconds, until it flashes “set.” Some DSLR cameras have more settings than this, allowing for cloudy (7000K) and overcast (9000K) conditions, among others. Some cameras allow you to manually dial in the color temperature you’d like. Maybe the presets are a little warm or cool for your liking, so you change the color temperature to a different setting.
Daylight refers to filming conditions outside, but what does tungsten mean? Tungsten takes its name from the tungsten filament found inside a normal household lightbulb. It is this filament that when heated gives off the orange glow. If you are filming inside with lights on, set your camera to tungsten. If you are filming outside, then set your camera to daylight. Now, the problems arise when you are mixing these sources in the SAME scene. What do you set it to?
Consider this chart a simple guide to what color casts happen and when.
Camera setting Source light Color cast
Daylight Daylight None
Daylight Tungsten Orange
Tungsten Tungsten None
Tungsten Daylight Blue
You might have already seen this happen in the projects you may be shooting. You’re filming inside on a tungsten setting and a window gets in your frame, allowing daylight to creep into your shot. This daylight now looks all blue. Or vice-versa: You may be filming outside and someone in a nearby house has a light on; this light will then look a little orange. Mixing these color temperatures can be troublesome if it’s not the look you’re aiming for. This is where color-correction lighting gels come in. Here’s an example of a shot in daylight conditions, but with the color temperature set to tungsten. See the blue cast?
Lighting gels come in various types of colors and strengths. There are simply too many to list, so we will focus on the main set you might find yourself requiring. Gels can be used for correcting the temperature of the lights you’re using, or simply for creating mood. Maybe you don’t have a color cast problem as all the lights you are using are tungsten, but you want the one at the back to be red and the light above to be a little green . . . Who knows? This is what is so great about cinematography: it is all down to the choice of the artist.
Some common lighting gels are:
Full CTB (Color Temperature Blue) — Used to convert tungsten sources to daylight or to turn HMI sources blue, to create moonlight, for example.
Full CTO (Color Temperature Orange) — Used to convert daylight HMI’s to tungsten, or to lower the temperature of tungsten sources to sunrise / sunset, for example.
Neutral Density (ND) — Reduces the intensity of light without changing the color.
They are very similar to the ND filters in the camera but this time in dark gray gel form for lights. These gels are used to adjust the output from just one light in a scene, whereas adding ND in the camera will adjust the output of all lights by darkening the image overall. ND gels also come in various strengths to reduce intensity. The 1-stop change listed below is equivalent to what you would have to do to your camera’s aperture to get the same effect.
ND 0.3 (1-stop change)
ND 0.6 (2-stop change)
ND 0.9 (3-stop change)
Diffusion — Diffusion is a white or frosted gel, a little like tracing paper. It is used to soften or “diffuse” the light from a hard source. This gel can be clipped to the front of a light or be made into a larger frame to be positioned in front of the hard source light to make it soft. There are many types of diffusion, and varying strengths.
PUTTING IT INTO PRACTICE
Let’s assume you are filming inside and there is daylight coming in the windows for a good portion of the shot. The scene has no practical light from bulbs or lamps, so it is a little dark. To bring up the exposure, we bring out one of our lights, maybe a 2K blonde. This light is tungsten-balanced; left uncorrected, it will read orange in the image when our camera is set to daylight (which it should be, as most of our light in the scene is daylight sourced). To move the color temperature of the blonde light up toward daylight, from 3200K to 5600K, we could add a full CTB gel. A full color temperature blue gel would convert the tungsten light to daylight so its output would match the light from the window. Now we can light our scene, whatever that might be, and everything will be even from a color temperature point of view. But sometimes daylight isn’t 5600K. Throughout the day it does go up and down, as we can see from early morning and evening times on the chart. So if the daylight at the time is more like 4600K, we could try putting a 1/2 CTB on the blonde, which would only half convert the blonde to daylight. This is all down to your judgment.
The alternative would be to rent an HMI (Hydrargyrum Medium-arc Iodide) daylight- balanced light, and then you won’t need to correct it at all.
Let’s look at another example. Say you’re shooting a candle. I personally want that candlelight to read a little orange. Candle light is 1800K on your color temperature scale, lower than a 3200K tungsten setting. Remembering that every source that is lower than the camera setting is going to read a little orange, I know if I set my camera to tungsten, that candle will read a little orange since tungsten is a little higher on the scale than candlelight. However, if I did a white balance card reading in that environment, the camera would see the present orange cast and electronically add blue to the mix to balance the orange tint and make the scene more white. The camera thinks it’s helping you by eliminating the color cast the source is giving you. I don’t want my candle to be white; I want it orange. Remember, if the source light matches the color-temperature setting on the camera, any white light will read as white. In our candle situation, when white balancing, the camera would be set to about 1800K, casting out our orange light for good! So what would happen to our candlelight if the camera was not set to tungsten, but to daylight? Remembering every source lower than the camera setting gives off an orange tint, the candle will now read as . . . VERY orange. This is something you might want to try. If you were shooting on a camera with color-temperature adjustment, you might find 3200K at tungsten not orange enough, but a 5600K daylight setting too much. So you could dial it down to 4000K. Then you might have an orange tint you are pleased with.
Candle with color temperature at 1800K.
Candle with color temperature at 5600K.
Have a look at this illustration of a house at Christmas. Say we want a Christmassy feel to this shot, and that the director has asked for the exterior to be a little blue, as if the moon is casting a blue tint over everything, while the interior needs to have an orangey glow from the fireplace. You could pretend we’re making a Christmas ad for TV. How can we use our lights, gels, and camera settings to achieve this?
We have a blonde (tungsten) light inside the room to lift exposure and to simulate our light from the fireplace. The fire itself wouldn’t give us anything bright enough to really use, so we’d enhance it artificially. Now, do we need to gel this light? To give the feel of firelight and make it look warm and cozy, the camera’s white balance must be set properly.
We have also placed an HMI outside to light the side of the house and give our moonlight effect. Do we need to gel this light too? Let’s have a look at the two scenarios.
Camera Setting 1: Tungsten
With this setting, the blonde lamp inside will need gelling with CTO since the camera and source light will match. Will the HMI outside need gelling too? Well, maybe not, since the HMI will automatically give a bluish color cast with the camera set to tungsten. If, however, for artistic reasons you wanted it to look even bluer (sometimes referred to as “American night” since Hollywood movies always seem to have blue moonlight), you could add a little CTB to help, maybe a ¼ CTB.
Camera Setting 2: Daylight
If we set it to daylight, the blonde lamp inside will give off an orange cast naturally, so you might not need to gel it if it’s giving you the look you are after. The HMI outside, though, will now be reading as white light (since camera setting and source match) and will not produce the blue-moonlight feel the director is after. You might need to gel the HMI a ¼ or ½ CTB to give it that moonlight feel.
To see color temperatures in action, take a look at this screengrab from the film The Patriot (2000) featuring Mel Gibson. Here we see candles and moonlight in the same shot, mixing color temperatures.
"Shooting Better Movies: The Student Filmmakers' Guide" is published by Michael Wiese Productions and is available to buy from Amazon here: