  Optical coatings are widespread in everyday life, from camera lenses to
glasses, to complex optics experiments. A simple, reliable device that can
quickly and inexpensively analyze optical coatings is a valuable laboratory
tool. Such a device can identify unknown or mislabelled optics, and
characterize the transmission spectra of optical elements used in an
experiment. We present the design and characterization of a LED-based
spectrophotometer, and demonstrate its ability to identify different optical
coatings. Our approach uses ten LEDs that cover a spectrum from 365 nm to 1000
nm. A small servomotor and microcontroller rotates a LED board to sequentially
position each LED over an optical sample, and the transmitted light
corresponding to each LED is measured with a silicon photodetector. The device
is automated, portable, inexpensive, user-friendly and simple to build.
