Light sensors detect the intensity or brightness of a light source. Light is often measured in Lumens, a which describes how much light is emitted from a source, and Lux, which describes light intensity measured over a specific area. The light sensors used in this activity digitally measure Lux by measuring the intensity of light that reaches a defined area on the surface of the sensor.
Visible light exists on the electromagnetic radiation spectrum and has a specific range of wavelengths between about 400-700 nanometers (nm) long. On the smaller end of the spectrum, is ultraviolet light (down to about 300 nm) and on the longer end of the spectrum is infrared light (up to about 1000 nm). Light sensors often detect the intensity of light across a specific range of wavelengths. Sensors that detect the full spectrum of visible light measure light intensities across all wavelengths between 300-1000 nm. Some light sensors measure light intensities of a subset of those wavelengths so as to measure the intensity of just ultraviolet light or infrared light.