This conversion from our sensor's output will give you an energy across the entire UV waveband. The multiplier provided is based on an average wavelength of 350 nm which is the weighted average wavelength of UV our sensor reads. This conversion is suitable only when using this sensor in sunlight.
Multiply the sensor out (in µmol m-2 s-1) by 0.342 J µmol-1. this will give you a number in J m-2 s-1, which is actually W m-2.
1 W m-2 = 0.1 mW cm-2 = 100 µW cm-2
If a more precise conversion is required, or you are using this sensor under supplemental lighting, not only would you need to know how much total UV is present (what our UV meters show you), but also the distribution of UV (i.e. the breakdown of what specific wavelengths of UV you have). A spectroradiometer can provide this type of information.