A variety of applications for UV LEDs that are integrated into a system are described, where the UV light is used for disinfection of air or surfaces, or used to detect the scattering light by particles, or used for skin treatment. In one embodiment, a ceiling luminaire includes a sensor for detecting the presence of people in the room. The luminaire contains a first set of LEDs for generating white light, for illumination, and a second set of LEDs for generating UV light for disinfecting the room. When the sensor detects that no people are in the room, the system automatically controls the UV LEDs to turn on to disinfect the room. The white light LEDs may be independently controlled with a dimmer.