Use one kind of lighting for accurate color

 This is part of a series of posts on how to photograph art.
The various types of lighting available today have different color characteristics. Fluorescent lights often have a cool and slightly blue appearance while tungsten lights tend to lean towards the warm end of the spectrum. The human mind will perceive the light emitted by both types of bulbs as "white light" but the differences in color will be exaggerated by the camera. This post is part of a series about how to photograph art.



I demonstrated this concept by photographing a white wall with a mix of incandescent and fluorescent lighting. In both pictures are two lights pointing down at a white cinder block wall. The light on the left is a “Daylight” CFL with a color temperature of 5500K which is a close approximation of daylight. On the right is a household tungsten light bulb that has a color temperature of approximately 3200K.

I set the white balance in the first picture to the “daylight” to match the color temperature of the “Daylight” bulbs. When I took the picture the daylight CFL on produces neutral white light as expected. However, the tungsten light on the right has an unexpected orange color cast.

Daylight compact fluorescent bulb on the left
Tungsten light bulb on the right
Shot using Daylight white balance

I took another exposure while leaving everything the same except that I set the white balance to tungsten. The light on the right now appears neutral but the light on the left has a strong blue color cast.

Daylight compact fluorescent bulb on the left
Tungsten light bulb on the right
Shot using Tungsten white balance

This is confusing because it’s different from how it's perceived by the human eye. When I took these pictures neither of the lights appeared to have an orange or blue color cast. I could discern a subtle difference in color but it wasn’t as exaggerated as in the photographs.

The point is that it’s nearly impossible to achieve accurate color if you use light sources with different color temperatures. If you make adjustments for one light source, the color will then become wildly inaccurate for the other light source.

Combining light sources can happen by accident such as when your photography setup uses fluorescent lights and you forget to turn off the overhead tungsten lighting. Light sources are mixed intentionally by amateur photographers in attempt to increase the brightness. For example, an artist might photograph a painting with a combination of natural daylight from a window in combination with light from an incandescent lamp. If you have ever tried this I’m sure you were disappointed with the results.

To avoid mixing light sources, it’s best to utilize a room where you have control over the lighting. Block out all extraneous light sources and turn off the over head lights. Shooting at night is an option if you have a sky light or a window that can’t be easily blocked out.

Fluorescent lights are available in warm, cool, daylight so make sure that you’re using all of the same kind. If you’re not sure look the color temperature is often printed on the plastic base of the bulb. Also, the fluorescent white balance setting is only accurate for the cool white fluorescent bulbs.

While mixed lighting is a problem when photographing artwork, this concept can be used to your advantage in other photography genres. Mixed lighting can often be seen in architectural photography, especially with interiors that are photographed in the evening. The interior of a home may be lit by tungsten lighting and the tungsten white balance setting will make the scene outdoors appear more blue, especially in the late evening.