Answer to Question #12178 Submitted to "Ask the Experts"

I want to build a bacteria-killing filter for a pool and fish pond. Would acrylic plastic about 1 centimeter (cm) thick prevent ultraviolet-C (UV-C) radiation from passing through? The alternative is probably quartz glass, but the advantage of acrylic or Plexiglas is that it is easier to work with.

UV-C light is a very energetic form of light that is not visible to the human eye. Based on our evaluation, UV-C light which is used for germicidal processes will not penetrate standard acrylic plastic sheets, so they will not work for your proposed application.

UV light, a form of energy, is defined as light having wavelengths between 100 nanometers (nm, 1 billionth of a meter in length) and 400 nm. (For reference, the human eye is sensitive to light between about 400 nm [blue] and 700 nm [red]). UV light is further divided into UV-A, UV-B, and UV-C light. The wavelength of UV-C is 100 to 290 nm. In general, UV-C does not penetrate the earth's atmosphere (please refer to Ask The Expert Question 12082.

The ability of UV-C light to penetrate materials will depend on the chemical composition of the materials. Most acrylic plastics will allow light of wavelength greater than 375 nm to pass through the material, but they will not allow UV-C wavelengths (100–290 nm) to pass through. Even very thin acrylic sheets of less than 5 millimeters (mm) do not let UV-C light penetrate. Therefore, you will not be able to use standard acrylic plastic for your application.

Because the ability of UV light to penetrate acrylic plastic is dependent on the chemical formulation, you may be able to find plastic sheets that will allow the UV-C to penetrate. If you would like a more technical discussion on the transmission of light through acrylic plastics, please go to the Cole-Parmer website.

Paul A. Charp, PhD