[KennyBlanken]

You'll note the installation location - in the evaporator unit. It's to reduce mold growth in the evaporator unit, not sterilize air.

UV units intended for installation in return or supply ducts are snake oil. A waste of electricity and money (the bulbs have a pretty finite lifespan.) The velocity of air in most ducts is such that anything flying by wouldn't be sterilized, and you can just install a large air filter (like the Aprilair 413 others have mentioned) and it'll bring a lot more benefits to the table, namely much better reduction of dust.

The greatest problem with indoor air quality is offgassing of VOCs and other pollutants from construction materials, furniture, electronics, etc.

If you want the best indoor air quality: install a large filter like the Aprilair or some equivalent, an air exchange device, and if you have a gas stove/oven, switch that to electric.

[lightedman]

"UV units intended for installation in return or supply ducts are snake oil. A waste of electricity and money (the bulbs have a pretty finite lifespan.) The velocity of air in most ducts is such that anything flying by wouldn't be sterilized,"

If you just do the simple thing and point the lights in a self-facing ring in the duct, no, they will not work. The trick is to beam the light down the incoming pathway to drastically-increase the exposure time. Clean reflective surfaces in the ducting to even out the photon flux density will greatly help with this.