here is how a police helicopter works...
first it can only read surface temps of your house.... this means they only "see" the outside of the walls or the roof... during the summer it isnt an issue as roof temps can easily hit 150f+... and exterior walls can get quite warm also...
in the cooler months what they look for isnt the heat signature from your lights, but whether you have a room that shows up noticably warmer than other rooms in your house.. this really only affects the top story rooms in a 2 story house as it is hard for them to get a good reading on the side of your house if you live in a neighborhood due to having neighbors...
now lets say they find a room that shows up warmer.. then they might start investingating it by sending the chopper over it at different times to see if there are heat patterns that would be consistant with a grow op... if the room shows up warm on a 12/12 cycle or 18/6 cycle, for example, then they may further investigate...
they will also look for flurs, which are spouts of hot air, leaving a room... your dryer vent creates a IR flur if you were to look at it... more than 1 flur, a flur somewhere where there is obviously going to be no dryer at, or flurs that are at timed intervals from exhaust fans being on timers are also good indications of a grow op...
usually even with all this "evidence" they still need more to get a warrant... so they may send a cop to walk around the premisis to see if they hear, smell, or see anything that may resemble a grow op.. if they do, they proceed from there to try to obtain a search warrant...
now if you are an attic grower it causes a little more of a problem because directly above your lights can easily create a hot spot that would appear on your roof.. it is important to light cool your lights in your attic to keep the hot spots from appearing, have good air circulation to keep the air temp in the attic even, or cover your interior of the attic with IR blocker... this keeps them from being able to read any further in than the blocker is setup...