A Low-Cost Quantitative Absorption Spectrophotometer

In an effort to make absorption spectrophotometry available to high school chemistry and physics classes, we have designed an inexpensive visible light absorption spectrophotometer. The spectrophotometer was constructed using LEGO blocks, a light emitting diode, optical elements (including a lens), a slide-mounted diffraction grating, and a photodiode detector. The photodiode detector was mounted on a rotatable arm for wavelength selection based on elementary laws of diffraction. This simple design demonstrates basic physical principles (such as diffraction and absorption of light) that are frequently lost in commercial "black box" instruments. The homemade spectrophotometer's performance, as measured by comparison to a commercial spectrophotometer, was shown to be sufficiently quantitative to facilitate experiments in chemistry or physics classrooms.