UV light bounces around just like visible light, so reflected or ambient light works fine to activate PURETi.
There is a range of functionality that PURETi delivers that depends on the amount of light it receives.
Outdoors – PURETi claims a full set of self-cleaning and air purifying benefits. These functionalities only require 0.1mW/cm2 of UV-A light. Direct sunlight delivers over 1mW/cm2 and the north side of buildings – even in the shade – receive more than 0.001mW/cm2 of UV-A light.
Indoors – PURETi claims a more limited, but still powerful and highly marketable, set of odor eliminating and IAQ, respiratory health improving benefits. These functionalities only require 0.001mW/cm2 of UV-A light – one hundredth the amount of light required for full self-cleaning. This level of light is found at window surfaces and light fixture surfaces.