Introduction to White Light

Did you know that white light is actually a combination of wavelengths of colored light? When many colors of light enter your eye, the eye registers it as white light. You can see this effect by simply allowing sunlight to refract through a prism. Different colors, or wavelengths, will bend at different angles, creating a rainbow.


If you look closely at the rainbow from your prism, you’ll see that it’s complete and has a fairly even intensity. However, using your light bulb as a source of light might show you something different. Light bulbs may show greater intensity in certain colors of light and weaker intensity in others. Traditional incandescent lights exhibit greater intensity at the red end of the spectrum. Other bulbs emit several discrete wavelengths, which the eye perceives as white. A continuous spectrum, without any gaps, is ideal for viewing gemstones. Note the differences between the spectra of these lamps shown below.

Images © Iain Mason. Used with permission.

Spectral Power Distribution

For understanding the intensity of different colors in white light, the spectral power distribution (SPD) is essential. While most artificial lights have peaks and troughs in their SPD, sunlight…