Color Perception or Misperception

January 28, 2013

Lightbulb2 (2)

Photographer: Tommy Hornbeck
Summary Author: Tommy Hornbeck

We recently bought a variable color light bulb that displays a beautiful rainbow of color, covering the full visible color spectrum; I thought. Closer inspection showed that the bulb has only three colors and that only one color was on at any given time. The picture above shows some of the properties of light and the way our eyes perceive light that we think we see. It's but one photograph of a single, variable color light bulb; not a montage, collage, or stitched together patchwork. The light bulb contains only three Light Emitting Diodes, red, green, and blue that are rapidly pulsed off and on in varying patterns to simulate the full spectrum of colors as shown in the color bar at the top of the photo including wavelengths from around 390 (violet) to near 700 nanometers (red) -- one nanometer is one billionth of a meter.

By very rapidly panning the camera with shutter open across the light bulb, I recorded nine samples on a single frame. This had the effect of stretching time and helped to convince me that there's never more than one color on at any given moment. Nevertheless, our eyes enjoy a beautiful full range of colors. Note that on the bottom line the red, green and blue lights are on at the same time to simulate white.

The human eye only has color receptors for red, green, and blue light. When all three are mixed, our eyes perceive the color purple. Mix red and green and we perceive yellow. Within THIS light bulb however, red, green, and blue are never mixed (except for white light). Our eyes cannot tell if a color is produced by a single wavelength or a mix of wavelengths and are here simply fooled into seeing what isn't there by the rapid switching between the three LEDs. So the next time you think you see a display of beautiful colors, remember, they may not be there at all; it might be all in your mind. Photo taken on January 16, 2013.

Photo details: NIKON D-80 camera; 16mm lens; f/22; 40 second exposure; ISO 100.