Why are dimmers de rated for halogen lights when they are just filament bulbs? I can understand for l.v. halogen when there is a transformer in the cct, but not for mains halogen as normal incandescent bulbs aren't derated. Also, what are the best dimmers for feeding l.v. halogen light fittings that contain toroidal transformers? The light in question has 4 x 50w 12v halogens in it