How to measure UV light intensity

Updated February 21, 2017

UV light intensity is monitored for several reasons. The main reason is to assure that people exposed to UV light are not harmed by the rays. But since UV light rays serve as light-curing devices for inks and resins, killing bacteria and sun tanning among other uses, the effectiveness of the UV light can also be determined by measuring its intensity. Manufacturers' specifications for a UV light source are critical as a reference point, and basic safety guidelines must be adhered to as well.

Obtain a radiometer. You can find them at science and medical stores, and they are also available online.

Plug in the probe and turn on the radiometer. It will be precalibrated from the factory.

Hold the probe next to a UV light source and read the light intensity measurement on the screen. In commercial working environments, the recommended dose of UV intensity that contacts your skin must read less than 1 mw/cm squared. (That reads out as "one milliwatt for every centimetre, squared.") A typical sunny day has a light intensity of between 2 mw/cm squared and 6 mw/cm squared. Pathogen-killing UV intensity is approximately 40 mw/cm squared.

Check the function of the equipment. If the light intensity does not meet the manufacturer's specifications for that particular light source, the UV bulb needs to be replaced.


Radiometers measure different UV intensities for different functions. Choose the type that is applicable for your needs.

Things You'll Need

  • Radiometer
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About the Author

Dale Yalanovsky has been writing professionally since 1978. He has been published in "Woman's Day," "New Home Journal" and on many do-it-yourself websites. He specializes in do-it-yourself projects, household and auto maintenance and property management. Yalanovsky also writes a bimonthly column that provides home improvement advice.