Hazza - I have tried HID, CFL and LED. The HID (250 watt) drove the temperature in my grow cupboard too high and heat-stressed the plants. (Remember I only have 600mm by 600mm about 2 foot by 2 foot). I then used a 350W CFL for flowering (which worked quite well). I currently an using a Vipar LED as my main light. This really pumps out the light.
http://www.viparled.co.uk/collections/series-b-1/products/vipar-b2x2-led-grow-light I also use a couple of 50W Procyon lights as supplementary side lights
http://www.homegrownlights.com/50wled.html I used these to supplement my CFL grow but so far I have not needed them with the Vipar yet as it covers 2ft x 2ft at the required light density.
Remember to keep a lot of air moving over the plant/s. This has four functions: 1 It stops mould forming in your buds, 2 It helps the plant/s stay cool and avoid heat-stress, 3 The more air is pumped over the grow the more dilute the heat-signature, 4 a good air-flow discourages pests like spider-mites.
I do not know how many plants you are growing or what space you are trying to cover. Remember that it is better to have one really good plant than two poor ones. If you get busted then number of plants matters. I opted for fast growing feminised automatics. I have been using Sharkbite and it has worked quite well.
The more you can disperse the warm air from your lights the better. Every house produces heat so if you can disperse it, the FLIR will not be able to pick it up as a suspicious item. Think of a tumble drier pumping out 3KW of heat, or the vent from a central heating boiler at 5KW. Your grow will probably be a lot less than this so it is not easy (or perhaps not possible) for the police to find a small grow on a casual fly-over. Spanky made a good point when he wrote that the main danger is being ratted out and the FLIR used as a cover by the cops so the grower does not go looking for the source of the information.
I recently watched a police documentary on the operation of a FLIR chopper. They were indeed working on "information received". They were watching a specific house. In IR the eves of the attic lit up like a Christmas tree! They were pumping many Kilowatts of hot air into the attic. This was a no-compromise commercial grow run by illegal aliens.
I am interested in your cooling tower. How does this work?