Understanding White Balance or Color Temperature

The Color of Light
Everyone has taken at least one photograph that has been way off in color. You get it back from whoever processed it, or if it is from a digital camera you load it into your computer, and your immediate response is “what the heck happened?”. Everything has a weird color cast to it, either orange, green or blue.

Light has a definite color to it depending on the light source and it’s surrounding conditions. As humans we don’t recognize the changes in the color of light, for the most part, because our brains adjust for it.

The color of light is measured in degree’s Kelvin. This is referred to as color temperature. The lower the color temperature, the redder the light is. The higher the temperature, the bluer the light is.

Let’s look at sunlight. Throughout the day the color temperature of sunlight changes because of it’s angle and the surrounding atmospheric conditions. Early in the morning and late in the evening sunlight gets a warm golden glow to it. Photographers refer to this time as the golden hour. During the middle of the day however the light is very blue, around 5500-6500 degrees kelvin. This is the color temperature of most flash units. In the shade, the color temperature of light is around 7500 degrees kelvin.

Artificial light on the other hand is a whole different ball game. Let’s take a look at incandescent light bulbs. These are every day light bulbs. On average the color temperature of a light bulb is around 3200 degrees kelvin. They have a strong orange color cast. This is evident if you are outside, late in the evening and look at the windows of a lit up house. The light in the windows will have an orange cast that is very easy to see. It used to be that florescent lights were at about 4000 degrees kelvin. This color temperature would record with a green cast on daylight balanced film. These days florescent lights can be purchased at different color temperatures.

The Recording Media and Corrective Options
Because of the way light can shift color a white object may not record as white on different recording media. As far as this article is concerned, there are two types of light recording media. One is photographic film and the other is a digital camera. Let’s look at film first.

Photographic film records the light that is reflected off an object. If the object is grey, how do we get the image on film to be grey, if we don’t know what color the light is that is hitting the grey object and reflecting onto the film? Film manufacturers have basically solved this problem by calibrating the film to a certain color balance or color temperature. You have two choices, daylight (5500 degrees kelvin) or tungsten (3200 degrees kelvin). So if you are shooting film outdoors, you would choose daylight balanced film. If you are shooting indoors, you would choose tungsten balanced film. Any deviation in color temperature from these two standards would have to be corrected with a color correction filter.

A digital camera works pretty much the same as film. The recording device in the camera has to be calibrated to the color of the light in order to get a neutral image. Neutral meaning no color cast. A white will record as white. Different digital cameras use different methods of letting you choose the color balance. Most digital cameras will have an auto white balance function. In most situations this works fairly well. However there are occasions when the camera can be fooled. This is why a lot of digital cameras also give you a way of setting the white balance manually. Either through a list of choices like daylight, shade or overcast, or a list of color temperatures such as 3200, 5500 and 6500. Some digital camera’s take it a step further and let you choose a custom white balance by having you photograph something white and use it as a reference for white balance.

Getting Creative
By using the white balance in your digital camera you can “set it wrong” to create different moods of light in your images. As an example, lets say you are photographing a field covered in snow on a sunny day but you want the image to reflect the fact that it is only 10 degrees outside. If you were to set your digital camera’s white balance at anything lower then 5500 degrees kelvin the resulting image would have a blue cast to it making your image ‘feel’ cold. Experiment a little with it. Don’t just play around with aperture and shutter speed, play with the white balance too.


©2005 Ken Henderson