A reflectometer, also referred to as a spectrophotometer, is an optical instrument used to measure the intensity of light through a solution or object as a function of the light's wavelength. They are typically used to measure how reflective a particular solution, glass object, or gas is. Reflectometers also measure the diffusivity of light for each of the known wavelength ranges.
There are two different parts to a fully functional reflectometer — the spectrometer and the photometer. The spectrometer produces light of any wavelength, and the photometer records the intensity of the light. To use the instrument, the test subject is placed between the spectrometer beam and the photometer. The intensity of the light is absorbed by the photometer, which then sends a voltage signal to a galvonometer, a device used to display scientific results. As the amount of light absorbed by the solution changes, the voltage signal will change.
In optical reflectometry, it is possible to find the proportional relationship between the concentration of the solute and the intensity of the light from the spectrometer. The intensity of transmitted light through a mixed solution, that is, one with a colored solute, equals the intensity of transmitted light through the pure solvent, multiplied by ten to the negative power of the concentration of the mixed solution, times a constant and the distance that the light passes through the solution. This proportional equation is commonly known as Beer's law, an important principle in the field of spectrophotometry and light absorbance.
Within industry and teaching labs, many different types of reflectometers are used. One type of reflectometer that is frequently employed in academic settings is called the Spectronic™ 20 reflectometer or the Spectronic™ 20 spectrophotometer. To use, the instrument is warmed about 15 minutes before use. Next, the desired wavelength is set. For wavelengths in the more outlying ranges, special instruments, such as curvettes, must be used to accurately analyze the light sample.
Once the wavelength has been set, the reflectometer is tared to zero in order to ensure the most accurate spectrophotometric results. Next, the holding tube is wiped clean and the sample is placed in the tube. The light control knob is tared to zero on the absorbance scale. Before performing tests on desired solutions, scientists usually perform tests on a reference solution to provide a benchmark for future results. When the reference solution has been tested, recalibration can be done and the true tests can begin.