I purchased one of these for my backyard that is about 1/2 acre and has lot's of foliage and a koi pond.  I built a stand for it and placed it about 20' from our patio, on the oppsite side of the koi pond and it seems to work very well.  It utilze's an arc of electricity to kill the insects that are unlucky enough to go to the light.  There are verticle bars surrounding the lamp that when a insect touches two of the bars, the flowtron utilizes the insect to complete the circuit until there isn't sufficient insect left (burnt up) to continue the arc.  Generally this is a fairly quick process (ZAP) however the occasional moth or larger bug will fly in and you'll hear a nice zaaaaaaaap or sizzzzzzzle until enough is "gone" to break the arc.