Figure 5: The light spectrum from an incandescent bulb.

When we view an object, the color we perceive depends on the light source. Light emitted from a common household incandescent bulb provides more illumination in the red region of the visible spectrum, as shown in Figure 5. The fluorescent bulbs used in many commercial settings strongly illuminate the green and blue regions (Figure 6). A ripe apple will appear redder in incandescent light than when viewed in fluorescent light. Natural daylight provides a more uniform distribution of the viewing wavelengths, but peaks in the blue-violet region (Figure 7).

Because the color we see depends on the light source, we find that a pair of colors may look the same in one light source, but not in another. This phenomenon is termed “metamerism.” For example, the color of a sofa that matched a swatch of curtain material in the store (fluorescent light) turns out to be a poor match to the curtain when brought home and compared in household incandescent light.

Figure 6: The light spectrum from a fluorescent bulb.		Figure 7: The natural daylight spectrum.