There are very sophisticated programs to calculate the lamp sizes and in-air dose requirements in terms of energy required for space and radiant fluence (joules per square meter, J/m2) across a cross-section of a UV-C beam, but there is a much simpler evidence-based dose that has been developed over many years for TB control, typically specified as about 17 mW of 254-nm lamp-emission radiant power per cubic meter (m3) of space to disinfect air.13 Although this sounds too simplistic to be true, since air in any room is always moving and mixing, one can correctly assume that all air will be treated—the better the air mixing, the sooner this will happen. Studies at the Harvard School of Public Health13,14 and elsewhere show log units of reduction equivalent to 24 ACH to achieve 80% reduction of transmission. Of course, 100% reduction is not possible, because of the multiple modes of transmission. To disinfect surfaces, this depends on the type of surface and its cleanliness; recommended exposures vary from 200 to 1,000 J/m2 (20 to 100 mJ/cm2).