A page from the "Causes of Color" exhibit...

What does our eye see in different lights?


Spectra of light reflected from a piece of white paper. Units of radiance in W/m2/sr/nm.

Different light bulbs create very different colors.

You’ve probably experienced the inviting warmth of a living room and the harsh coldness of, say, a doctor’s office. What you see (and how you interpret it) often depends upon the source of light.

Different illuminants

What we see depends on the illuminant. The most common type of light is the standard tungsten light bulb. Halogen light and candlelight are very similar, with halogen having a slightly steeper onset in the short-wave region, and candlelight having a concave, almost exponentially rising curve. When electric current passes through the gas of a fluorescent light, it produces ultraviolet light, which strikes a phosphor coating, making it fluoresce. An overcast sky creates a different kind of light. The light of a blue sky has a flatter spectrum across all wavelengths, whereas the light coming from grey clouds at midday is more intense in the middle and long-wave regions than in the short-wave region. Dips occurring at 690, 730 and 760 nm are typical for all daylight spectra and probably indicate the absorption spectra of compounds such as water. An additional kind of lamp, used frequently in offices, stores, and to light public spaces, is the vapor lamp. Vapor lamps contain a gas under low pressure, but the gas glows with visible light when electricity passes though it. The color of the light depends on the gas. The first electric lamps, arc lamps, were first developed in the early 1800s. Later in the 19th century, the filament light bulb and the vapor lamp were developed. See the sections on incandescent light bulbs, vapor lamps, and color constancy for more information.

Following is a summary of the colors seen in the light box above.

BulbPurposeIn the light box above...
Daylight bulbImitates natural daylightThe colored walls around the bulb appear just as they would in daylight.
Regular incandescent bulbCommon household light bulbThe filament emits a yellowish-white light, and the walls have a strong yellow tint.
Mercury vapor lampFirst high intensity discharge lamps, but now sales of new MV lamps are banned in the U.S.Left wall is blue, but right is blue-grey. The light has no red, so the right wall cannot reflect it. Light has some yellow wavelengths, seen on bottom wall.
Low-pressure sodium lampSometimes used for street lightingThe colors around this lamp show that its light is an almost pure yellow. Controls light pollution because the monochromatic light does not interfere with astronomical observation.
High-pressure sodium lampStreet lighting in cities, sports arenasGive most objects a similar color as daylight.