text: The essential parts of a colorimeter are:
  * a light source (often an ordinary low-voltage filament lamp);
  * an adjustable aperture;
  * a set of colored filters;
  * a cuvette to hold the working solution;
  * a detector (usually a photoresistor) to measure the transmitted light;
  * a meter to display the output from the detector.
  In addition, there may be:
  * a voltage regulator, to protect the instrument from fluctuations in mains voltage;
  * a second light path, cuvette and detector.  This enables comparison between the working solution and a "blank", consisting of pure solvent, to improve accuracy.
  There are many commercialized colorimeters as well as open source versions with construction documentation for education and for research.