Research on UVGI air disinfection continues today. Although it is clear that UVGI can be effective in test chambers, engineering specifications for a given room application remain elusive and are currently based more on common sense and historical practice than on actual evidence. However, that evidence is accumulating, along with data on maintenance and safety in a wide variety of applications. It is now clearly understood, for example, that occupant motion and position within rooms greatly reduce the possibility of harmful overexposures to UV-C radiation in lower rooms.144 In practice, if upper-room UVGI systems are installed properly, UV radiation threshold limit values are rarely, if ever, approached, even using eye-level target values above those previously applied that assumed continuous eye exposure.
UVGI fixture designs are also evolving, becoming more efficient while remaining safe, but innovative designs are needed to further increase efficiency while keeping manufacturing costs low. Interest and investment by major lighting fixture companies is badly needed to stimulate further development; however, the cost of applying upper-room UVGI is an important factor—not in resource-rich countries, but in poor settings where UVGI is most critically needed to reduce transmission of TB, pandemic influenza, and other major airborne infectious threats. In these resource-limited settings, local manufacturers are needed to keep costs down. Finally, experts in the real-world application of UVGI are also needed, both in resource-rich and resource-limited settings. Once engineering specifications are better defined, however, interest by designers from the engineering, architecture, and lighting industries should follow.