A MULTIWAVELENGTH PHOTOMETER BASED ON LIGHT-EMITTING-DIODES

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