Most determinations made in the clinical laboratory are based on the measurements of radiant energy transmitted or absorbed under controlled conditions. The device that is used to detect tramsmitted or absorbed radiant light energy is called a spectrophotometer. Because this instrument is so widely used in the clinical laboratory, it is essential that the medical technologist has a good understanding as to how it functions.

1. Power supply and exciting lamp. Some supply of electricity to operate the exciter lamp is necessary.

2. Monochromator. Monochromator is a device for producing light of a single color from a impure source. The word monochromatic means “ of one color. the most widely used true monochromator is composed of an entrance slit, a prism or diffraction grating to disperse the light, and an exit slit to select the band pass.

3. Sample holder

3.1 A cuvette . It must be clean and free of fingerprints, etching, and clouding and that the sample and reference cells must be matched for transmittance.

4. Photodetector. A device for detect the light transmitted signal.

5. Readout device. In the past nearly all spectrophotometer used ammeters or galvanometers. Newer digital devices and printers have now replaced these, and many instruments relay their electrical output directly to computer circuits where calculations are performed, allowing direct reporting of sample concentration.