Dude with the right system 5-0 can detect the sweat on a mouse's balls! Depends on the Budget and Tech capabilities of your local Lawdogs. You can create a Thermal sheild by using Space-blankets placed strategicly.
If you use an oven thermometer(with metal casing), you can check the temp around the light. Do it in several places, then you will know how much heat is being given off. The fans that are used for circulating air in the grow area can help to dissipate the heat generated by the light. That is also another reason the fans are used, they keep the plants from getting to hot, General rule of thumb is 70-80deg. and 40-80% humidity, These numbers are from Marijuana Growers Guide by mel frank. You might want to puchase the book at barnes and noble it runs about 20$ and is well worth the reference material in it. As far as the infared thing goes, I can't imagine them checking out yur house without some other reason first. Like unusual electric bills(takes alot of lights and stuff to cause this tho), there are several reasons use your imagination and u can hide any odd situations that cause suspision. I placed my grow box under a heat run from the furnace, hopefully this would throw off any would be McGarrets from poking around the place. I also use the same room as my music room, it contains amps and lots of electrical equipment that throws off more heat than the grow box does. It also explains my electric use and the fans in the room. hope this helps.
Most "LEO" setups mainly target the temps produced from 1000w systems,,,mainly the bulb,,,due to the intense temps within the arc tube(hottest part of HID setups). A cooler airspace between the heat source and the outer limit(or wall) will help throw off reading from infrared scanner,,,by eliminating the "hot spot" from showing on scanner. FYI ...The Supreme Court has determined that evidence obtained from infrared scans unconstitutional,,,and is not admissable as evidence for prosecution. Still.....be cautious