Good results are obtained with this form of disinfection because air has a low absorption coefficient and hence allows UVC to attack microorganisms efficiently.
Presently, there are five basic methods of air disinfection using ultraviolet lamps namely:

1. Ceiling or wall mounted UV lamps

This method is used in those cases where either the interior is unoccupied or where it is possible for the occupants to take protective measures against radiation.

2. UV lamps in upwards-facing reflectors for upper-air irradiation

This method of disinfection can be used to combat bacteria and moulds. It also has the advantage that it can be used in occupied interiors without the need of protective clothing.

3. UV lamps, incorporated in stand-alone air cleaners with a simple filter
In essence the units consist of UV lamps, mostly types driven by high frequency ballasts, mounted inside a »light trap« container.

Air disinfection
Traditional methods of disinfection of objects for example in medical laboratories fail to disinfect the air because microorganism floats completely free. Application of UV in air ducts for ventilation, heating and cooling purposes has proven to provide adequate protection against airborne pathogens. With patients and visitors bringing in pathogens that cause diseases such as tuberculosis, wards, clinics, waiting and operation rooms and similar areas should be protected against the risk of infection of personnel and patient populations. It is estimated that up to 99% of airborne pathogens are destroyed with adequate air circulation and UV exposure.

Cooling coils
Air conditioner cooling coils are almost always wet and dusty and thus can serve as an ideal breeding ground for moulds, a known allergen. Coil irradiation with UV drastically reduces or prohibits growth of moulds. At the same time heat exchange efficiency is improved and pressure drops decrease. As the coils are constantly irradiated, only a modest UV irradiance is required.