The video below shows an easy way to use your phone as a colorimeter, which can help you measure the concentration of substances in colored samples. To learn more about colorimeters, scroll past the video~

Materials needed:

• Transparent liquid container(s). The video uses cuvettes, which can be glass or quartz. Avoid using plastic since acetone can damage or melt plastic.
• Holder for container
• Sample solvent. This video uses nail polish, which contains acetone, a chemical good for chlorophyll extraction.
• White background
• Mobile phone with app that detects RGB values

More Detail on Colorimeters and Spectrophotometers

Colorimeters convert visible light into values that correspond with human perception of color, which typically means Red, Green, Blue (RGB) or Lightness, Red/Green Value, Blue/Yellow Value (Lab), and they are most useful in developing relative measurements of color intensity. Colorimeters are best used to compare similar colors and shades and to measure color strength. A really good use for colorimeters is to determine the relative concentration in solutions because there is a law (Beer's Law) that says that the more concentrated a solution is, the more light it will absorb. The video uses colorimetry to measure the concentration of chlorophyll from leaves.

Typically, colorimeters provide a light source that is only of one wavelength, however, in this modified mobile phone version, ambient lighting is used, so you want to make sure this ambient lighting is as similar as possible across measurements of different samples. Avoid measuring samples at dramatically different times of the day or with different combinations of natural and artificial light.

So how is a colorimeter different from a spectrophotometer?

Colorimeters are simpler than spectrophotometers. Both colorimeters and spectrophotometers measure spectral information in visible wavelengths (which means your sample must have a color you can see), but while colorimeters only give you 3 values indicating the intensity of the 3 color components that make up the entire spectral profile, spectrophotometers will give you intensities of light at specific wavelengths. To do this, it uses a prism-like device that splits up the light into its "rainbow" components and measures the intensity of a wavelength or a narrow band of wavelengths. This post describes how light is translated into an electrical signal in more detail. You can also use the spectrophotometer to measure every wavelength to give you a spectral graph. With intensity, you can then calculate transmittance and absorbance of your sample.