Photographic Terms – White Balance

Here are two examples of the results of different white balance settings:

White balance is a useful term for the photographer, be it still or video, to understand. Back in the film days, there were 2 basic white balances available with a 3rd sometimes used by professional photographers. Most film was balanced or designed for either daylight or indoor lighting. Daylight balanced film was the most popular since most photographs were taken outdoors – early film was so slow (low ISO or ASA rating) that there wasn’t enough light to take photographs indoors.

The color spectrum is shown below. It is a portion of the electromagnetic spectrum, a range of wavelengths that covers energy from below radio waves through gamma radiation. What we call light centers on the output of the sun after passing through the earth’s atmosphere. As you move to the right, the wavelength shortens & the energy level increases. Infrared (IR) light is below the left side, Ultraviolet (UV) is above the right side.

The color of the light source providing illumination of a scene can have a pronounced effect on the colors we see. What we call “white light” can cover a range of sources from low wattage tungsten lamps to a clear north sky. Although both the sun & tungsten lamps produce a continuous spectrum of light the peak energy is not centered at the same point in the color spectrum.

The sun produces light with far more energy than a tungsten table lamp, so sunlight shifts towards the blue end of the spectrum. Because your brain automatically adjusts your perception of color as you move from one light source to another, you rarely notice the difference. The human brain is an amazing device! The only time most individuals notice a color problem is when the source of illumination is missing some colors. For example, standing under a mercury vapor street lamp will turn reds (such as lips) black because it produces very little red light. Check this link to see the spectrum produced by a clear mercury vapor lamp.

The term Color Temperature is used to describe the color of light sources. Color temperature is measured in degrees Kelvin, a system that places 0° at absolute zero or -273° Celsius / -459° Fahrenheit. The term was derived by heating a object (called a black body) that does not reflect light. As the temperature of the object increases it eventually becomes hot enough to radiate light. Think of an iron bar heated in a forge. The color of light produced by the object is determined by its physical temperature.

While some sources of light are at the same temperature as a black body, others such a fluorescent lamps produce the equivalent without actually being at that temperature. You can describe the sun or a tungsten lamp as a “black body” in that they are very close to the actual temperature of the color of light they radiate. A blue north sky as noted in the table below produces light at a color temperature of 11,000°K – obviously the sky is not at that temperature or we would all be burned to a crisp!

The term temperature can be a bit confusing, because although we use an increasing color temperature scale to describe a shift from red to blue light, we describe a higher color temperature as “cooler” and a lower color temperature as “warmer”. The warm & cool descriptions come from the perceptual and psychological effects of color, not the physical temperature. For example, you might associate warmth with fire (red), and coolness with ice (blue). Warm lighting shifts towards red light; cool lighting shifts towards blue.

A table of some typical values is shown below:

Although your brain corrects for shifts in light source’s color temperatures, film cannot. Manufacturers had to pick some values when designing the film emulsions. They settled on 5500°K for daylight & 3200°K for indoor or tungsten film. Back at the time when film had an ISO/ASA of 25 or less, commercial photographers would over voltage lamps to get more light from them. They only lasted a few hours, but produced far more light than a lamp operating at normal voltage. The increase of 200°K caused a color shift because the lamp filament was burning hotter, increasing the color temperature. For that reason, type A film was developed with a 3400°K balance to work with these lamps. Most film sold today is either 5500°K daylight or 3200°K tungsten. Since the flash tube used in your camera is a fairly close match to daylight, daylight film works with electronic flash. Prior to electronic flashes, flashbulbs were given a blue coating to shift the color temperature to daylight.

When making images from digital sensors, the color temperature of the light source must also be matched. The advantage of a digital camera is you don’t need to change film to adjust color balance, all you need to do is adjust the balance between the electrical signals from the individual color elements of the sensor. As you move from outdoors to indoors you don’t need to change film; just the camera settings.

Camera manufacturers use the term white balance rather than color temperature but they are describing the same thing. Most cameras have an automatic white balance mode. This generally works well for “normal” lighting, but can often give incorrect results when the light source or subject is unusual. Unfortunately, unusual lighting or subject matter is often the most interesting for the photographer. Better quality cameras allow the operator to choose a white balance rather than the camera. Either a dial or menu setting can be used to set the white balance. Most manufacturers use symbols to identify typical balances:

Some DSLRs allow the photographer to manually set a white balance, usually using a white card lit by the light source you are going to use for the photograph. This usually produces the most accurate balance.

It is worth experimenting with the different settings when shooting at night, close to sunrise & sunset, and other cases when your light source is not typical. I would also shoot at least one image with the camera set on automatic so you can evaluate the different results.

One last note – There are many reasons for using the RAW file saving format if your camera is capable of that setting rather than TIFF or JPEG. White balance is one of them. When you use the RAW format to save an image the white balance is adjustable during post processing. This allows for both course & fine adjustments to produce proper color rendition under difficult lighting conditions. While it is possible to color correct a JPEG or TIFF image, it is far more difficult than working with a RAW image. There are many other reasons for shooting RAW – I’ll save the others for a later post.