Fog appear only if the lights are turned on in bad weather.

The water is getting in from the rain somehow, maybe around the bulb or in through a vent, it is then getting heated and then condensing on the cold glass. It appears to be much more than just regular humidity. Before you turn the lights on, is water visible on the bottom, inside the light? Is it one or both head lights? My car has not had the modified vents installed and I have had no problems. Did you put the bulbs in correctly and get a good seal, as I see you put in HID bulbs.