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An example that uses an LED (light emitting diode) as light source to miniaturize the conventional large spectrophotometer was demonstrated by the development of a portable photometer with two LEDs as light source and its application for determination of iodine in edible salt and formaldehyde in the atmosphere, in situ. The high speed, good precision, and low cost distinguished the device from other methods. The RSD (n=8) for measurement of iodine in edible salt varied from 0.7% to 1.5%, and the RE (n=3) for formaldehyde measurement varied from 0.8% to 4.4%. The analytical results obtained were in good agreement with those obtained with a conventional spectrophotometer. The portable instrumentation was demonstrated to be suitable for the quality control of edible salt and ambient air, in-situ. [ABSTRACT FROM AUTHOR]