As mostly the killing of micro-organisms does not present a problem but more the sensitivity of the human skin to ray contact, the answer has been found in technology – which we call "Plafond Sanitaire". 

With this method a bacteria killing UV ray ceiling operates over the heads of the people throughout a 24h/day (please also see product info WR2000). In dependence to normal air convection inside rooms - round about 6 times per hour - airborne germs are conveyed upwards into the irradiation zone and thus get killed by the system.