This is an excellent application note from Luminus, manufacturer of the UVC-LEDs used in this project. 

UV-C LEDs for Disinfection and Sterilization

In their experiments, inactivation of  >99.999% was achieved in 20 seconds of exposure at a distance of 1cm. One of the goals in this project was to shorten the required exposure time, and if possible, increase the exposure distance to a more practical level without decreasing sterilization effectiveness.

The current used in this project is higher than in the note's experiments (500mA vs 350mA) to increase the output by about 40%. These LEDs have lenses which are focused onto a smaller area (60° vs 130°) for higher beam concentration. Manufacturers offer these devices in a range of power levels, with and without lenses.

The ideal result is >90% inactivation of microbes within 10 seconds at a distance of 2-5cm.