Hi Ulf,
Regarding heat, I think it might be a little more complicated. Electrical energy is converted into light AND heat. So for the same wattage, the more light you produce the less heat you produce, I think? However somehow I feel my 575W HMI produce more heat than the 650W halogen modelling light, so I'm a little bit confused.
I have another question about balancing tungsten light: what is the difference between balancing at light source (gelling the light) and balancing in camera (with lens filter) and balancing in camera (using sensor temperature setting/setting sensor white balance)? I understand that best practice should be gelling the light, but can we balance in camera sensor (setting to 3200K) to save those 2 stops of light loss?