The MicroLab Energy of Light Module contains six LEDs with wavelengths from blue-green (505 nm) to infrared (940 nm), plus a socket for a user-selected LED. Light is produced by an LED when the voltage applied to it exceeds the band-gap energy of the semiconductor.

The relationship between energy and color, wavelength, and frequency of light is illustrated by increasing the voltage applied to each LED until light is produced and then recording this voltage. A light bar indicates electron flow through the LED so that measurements can be made at low current levels and at infrared wavelengths.

Planck's constant can be calculated to within 10% by plotting energy with respect to frequency of light for each LED. The Energy of Light Module may be operated manually with a power pack and digital voltmeter, or under software control with a MicroLab Interface (Model 402, ML-507, or FS-522).