There have been many reports of people being investigated and busted for marijuana cultivation because their homes were monitored with an Infrared Heat Sensing Device.
It works like this; If the authorities suspect someone is cultivating marijuana, they set up surveillance of the home or building and use an Infrared camera to measure the amount of heat radiating off the structure. They then compare the targeted structure to surrounding buildings or homes to gauge what they think should be the normal amount of heat emitted from a particular structure.
In some parts of Europe, the authorities don’t even wait for a lead from an informant to give them the heads up, on a possible marijuana grow operation. They simply take to the air and use their high-tech surveillance camera and scan the roofs and walls of homes in residential areas and buildings. If a home is identified as a possible marijuana grow operation because of the heat radiating off the structure, that home or building becomes the target of further investigation and possibly a raid.
Using HID lamp will emit too much heat that could be inspected by infrared camera. Now, LED grow light could deal with very well because it is cool light source which make authorities can not find what you do inside. So more and more growers are replacing of their HID lamp by LED grow light.