A multi-wavelength photometer based on light-emitting diodes.

The light originating from seven light-emitting diodes of different colours is guided, one at a time, into a measuring cell by means of a fibre optic coupler. Detection is carried out with photodiodes which are connected to a log-ratio amplifier yielding direct absorbance readings. Optical filters are used to narrow the emission band from blue light emitting diodes as these bands are relatively wide compared to those of the emitters of other colours. An inexpensive and compact multi-wavelength photometer covering the visible range is thus obtained, which in many cases can replace a conventional spectrophotometer for absorbance measurements. The performance for a range of commonly used photometric analytical procedures is described and compared to conventional measurements with a spectrophotometer.