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Exploring & Measuring Light

Connect an LED to a voltmeter and you have a  light sensor. Use LEDs that emit different wavelengths of light (red, infrared, blue, ultraviolet, etc.) to detect and  measure the intensity of light of similar, but slightly  shorter, wavelengths.
It is now possible with inexpensive technologies to measure the intensity of specific wavelengths of light. Light Emitting Diodes (LEDs) were invented in the 1960s. An LED is a device in which electrical energy is converted into light in a very narrow range of wavelengths. They have been refined over the years, becoming smaller, more intense, and emitting light at a greater variety of wavelengths than ever thought possible.

An LED also operates in reverse: it converts light energy of a particular wavelength into electric current. The voltage generated is proportional to the intensity of light shining on the LED. The wavelength of light needed to produce this effect is approximately the same as the wavelength of light that the LED normally produces when operating in the electricity-to-light mode, but not identical. An LED that emits red light generates electricity from orange wavelengths of light.

More background information about LEDs


These LED explorations were based on the work of Forrest Mims whose website, can give you a richer content on the science behind LEDs. Some of the MVH activities are adapted from his work. Most of these explorations were used in the Global Systems Science (GSS) student series created by Lawrence Hall of Science.