He means to get it out of where there is UV light present. Most household lights put out none or very little but sunlight is really bad as the stronger UV will cause changes to the hop oils and produce a skunk odor.
Having the thermostat set might be OK or really bad depending on what it is set at. I keep my thermostat at 72F for the main living area but where I ferment my beer the temp is 62-65 and that lower temp is sufficient to make good beer. If I were to try to ferment where it is 72F, the yeast would produce off flavors as the faster activity of the yeast will drive the temperature too high. Depending on what the temperature is where you ferment the beer, simply setting the fermenter into a tub of water may be sufficient to maintain the beer temperature in a good range.
Each different yeast will have a preferred temperature range. You may have to look up the yeast you use to see what it is. Nottingham will ferment pretty clean over a wide range, from about 55F to 72F. The saison yeast I used a couple times liked finishing at 85.