How to Calculate UV-C Dose on a Surface

When UV-C fixtures or handheld devices are used to sanitize surfaces and objects, it may be useful to determine the UV dose applied and comparing that to tables of dose requirements for deactivating microorganisms.

Measure UV Intensity

To get accurate dose data you need to start with a UV-C detector. The detector needs to display an intensity reading measured in microwatts per square centimeter (μW/cm² ). The Zenith detector is one example of a UV-C detector that will work well for this purpose.

With the UV-C fixture or handheld device turned on, the detector should be placed as close as possible to the same distance away from the UV-C source (lamp) as when it is being used to sanitize surfaces or objects. The meter will display the UV intensity in μW/cm².

Calculate UV Dose

UV Dose = UV Intensity (μW/cm² ) x Exposure Time (seconds)

Exposure time is how long the UV light is ON and delivering UV to a surface. Start with 20 or 30 seconds. 

The result of this calculation will be a value expressed in  μWSec/cm².

Compare Dose Calculation to Dose Required to Disable Various Pathogens

This value can be compared to the table below for various microorganisms. To deactivate any of these organisms, the value should match or exceed the dose values shown. You can simply change the Exposure Time until you reach the dose value you need.