A reflectometer measures light intensity through a solution or object as a function of wavelength. It consists of a spectrometer and photometer, and is used to measure reflectivity and diffusivity. Reflectometers are used in industry and education, with the Spectronic 20 being a common type. Beer’s law is used to find the proportional relationship between solute concentration and light intensity. Before testing solutions, a reference solution is tested to provide a benchmark for future results.
A reflectometer, also known as a spectrophotometer, is an optical instrument used to measure the intensity of light through a solution or object as a function of the wavelength of the light. 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 light intensity is absorbed by the photometer, which then sends a voltage signal to a galvanometer, a device used to display scientific results. As the amount of light absorbed by the solution varies, 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 coming from the spectrometer. The intensity of light transmitted through a mixed solution, i.e., one with a colored solute, is equal to the intensity of light transmitted through the pure solvent, multiplied by ten to the negative power of the concentration of the mixed solution, for a constant and the distance a which 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 absorption.
Within industry and educational laboratories, many different types of reflectometers are used. One type of reflectometer frequently used in academic settings is called a Spectronic 20 reflectometer or Spectronic 20 spectrophotometer. For use, the instrument is warmed up approximately 15 minutes before use. After that, the desired wavelength is set. For wavelengths in the more peripheral ranges, special instruments, such as hooks, must be used to accurately analyze the light sample.
Once the wavelength is set, the reflectometer is zeroed to ensure the most accurate spectrophotometric results. Subsequently, the stand tube is cleaned and the sample is placed in the tube. The light control knob is zeroed on the absorbance scale. Before testing desired solutions, scientists typically test a reference solution to provide a benchmark for future results. When the reference solution has been tested, it is possible to recalibrate and begin the real tests.
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