How much UV "light" is required, and for how long, to disinfect a surface?

How much UV "light" is required, and for how long, to disinfect a surface?

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 Health[13, 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).[24]

[13] Mphaphlele M, Dharmadhikari AS, Jensen PA, Rudnick SN, van Reenen TH, Pagano MA, Leuschner W, Sears TA, Milonova SP, van der Walt M, et al. Institutional tuberculosis transmission. Controlled trial of upper room ultraviolet air disinfection: A basis for new dosing guidelines. Amer J Respir Crit Care Med. 2015;192(4):477-84.

[14] Miller SL. Upper room germicidal ultraviolet systems for air disinfection are ready for wide implementation (editorial). Am J Respir Crit Care Med. 2015;192(4):407-9.

[24] Jelden KC, Gibbs SG, Smith PW, Schwedhelm MM, Iwen PC, Beam EL, Hayes AK, Mar4on N, Kratochvil CJ, Boulter KC, et al. Nebraska Biocontainment Unit patient discharge and environmental decontamination after Ebola care. Amer J Infect Control. 2015;43(3):203-5.