This low cost spectrophotometer uses an infrared LED (light emitting diode) and phototransistor to measure the amount of light that passes through a liquid. A multimeter provides a numerical reading (in milliamps) that corresponds to the amount of light detected by the phototransistor after it is passed through a sample. More light passes through clear liquids than cloudy ones, producing a higher milliamp reading on the multimeter. Less light passes through a more concentrated sample, producing a lower reading on the multimeter.
Spectrophotometry is often used in the laboratory to calculate bacterial growth curves, perform starch assays, and measure protein concentration in a solution.
Step-by-Step Building Instructions
Setting up and Using the Spectrophotometer
The design for this spectrophotometer was adapted from The Bug that Eats Toxic Waste, by Dan Dillon, Bob Schumacher, and Dr. Brent Peyton. Their document details a multi–disciplinary, multi–day project that uses a spectrophotometer to chart bacterial growth curves.