It doesn’t add anything to the air, nor does it remove anything. It only kills it. They are considered 98% +/- effective. It also assists in removing certain odors; and mainly the ones that are prevalent because of live organisms. In some cases, UV has been known to remove odors from cleaning agents, smoke, adhesives, and others. It is important that the light be installed correctly and out of sight as it can damage certain parts of an HVAC system and can be damaging to eyesight. There are numerous ways that UV is being used around us; residential and commercial HVAC is one of many.