Camera 101: White Balancing

White is not always white in the camera?s eye

By Stephen Schleicher

White balance problems can be frustrating. When a videographer comes back from a shoot with video that looks blue because he didn't white balance the camera, or when the footage is green because of the lack of a simple button push, he'll see red faces on his fellow producers, directors and editors back at the production studio. In this latest installment of Camera 101, learn to keep faces their natural color -- both on and off-camera -- using proper white balancing techniques.

A short bit on light
I?m not a physicist, nor do I claim to be, but let?s take a very broad look at some of the properties of light that should help in our discussion of White Balancing.   The Electromagnetic Spectrum encompasses a whole range of frequencies all the way from Infrared on one end to Ultraviolet on the other.  Somewhere in the middle falls the visible light spectrum ? that light we see with our naked eye.

If you analyze the spectrum you see the Infrared are long waves that we generally perceive as heat.  As we move to the visible light spectrum, the first color we come to is Red, a very warm color.  As you move through the visible spectrum (you can easily remember the colors by thinking of my friend Roy G. Biv) the last color we reach is Violet, considered a cool color.  This then leads us off to the very short waved Ultraviolet light.  In other words, as the light gets brighter, the wavelength becomes shorter.

?This is all well and good, but how does it help in our discussion of White Balancing??

Patience, young videographer -- all will become clear in time.

Because we can relate heat to light (Infrared feels warm), light can actually be measured on a temperature scale developed by Lord Kelvin in the 1800s.  The Kelvin Scale (K) can be used to define a relationship between the heat property of the light and the color.  The lower the Kelvin temperature, the warmer (red/long wavelength) the light, while the higher the number, the cooler (blue/short wavelength) the light.

This scale becomes clearer when we examine the Kelvin Scale as it relates to particular light sources.

Let?s begin with an open candle flame.  To our eyes, it appears red/orange and is measured on the Kelvin Scale at approximately 1800K.  A typical household incandescent light appears yellow/orange and falls around 2800K.  Typical office fluorescent light bulbs fall in the 4000K range, which, as figure 01 shows is a greenish light.  I?ll speak more on fluorescent lights in a bit. 

Studio lights are balanced at 3200K (yellow), and are typically what we consider the ?happy middle?.

As we move outdoors (increase in blue light), the temperature value increases.  Average noon sunlight measures in around 5600K depending where on the planet you are.

It needs to be noted that daylight and sunlight are not the same.  Sunlight is the light of the sun, while daylight is a combination of sunlight and skylight.  It is important to make the distinction because as you move from a cloudless day, to an overcast day, the color temperature actually increases to anywhere between 8000 and 30000K. 

Why?  Again, I?m not a scientist, but if you keep in mind that light is scattered by the atmosphere, and that a cloudy day has more stuff (water particles, hydrogen, nitrogen, etc.) than a clear day, there would be an increase in blue light, hence the increase in color temperature.

As you can see from our lengthy discussion, depending on the light source used, the color of the light can vary greatly.