The most effective way to go is a cooltube or enclosed hood with a separate, closed air circuit. This is to say that the light gets its cooling air from outside the grow room and dumps warmed air back outside the room as well. This prevents air used for light cooling from mixing with the grow room airmass.
Use aircon if you must, but a closed air cooling circuit will prevent the aircon unit from having to shift heat from the lights out of the room's airmass. You'll find that if you have cooltubes and the ambient air you have available to draw into the room is at or under 23C, you probably won't need aircon.
Air-cooled lighting requires a constant air supply during lights-on. Chances are you won't need your aircon unit to run constantly. It is much less expensive on the old power bill to run a 150mm blower for the cooltubes (35W constantly during lights on) and another blower to exhaust the room (perhaps 200W, runs a few mins an hour). Will be much less costly than any aircon unit. No, cool air from an aircon system won't shatter an HPS lamp tube, but you don't want to connect the aircon unit to the lamp unless the aircon unit runs all the time that the lamp is on.
There are some grow setups where you just can't get air in sufficient quantity or low enough temp for cooling or have no way to get rid of it so it is not sucked right back into the grow. In those cases, aircon may be your only solution.
However, cooltubes where possible will cut the cost of using aircon- dramatically. The aircon unit will run only about 20% of the time it usually needs if it has to shift the lighting heat by itself.
