When the main lamp kicks on for my 30g it heats the room up uncomfortably. It doesn't really affect the water temp that badly but it's my office and I spend a lot of time there. For that, it's too much as well.
Yeah, most of the energy that is not converted into light is converted into heat instead, so for that metal halide, 75% of the energy used is converted into radiation. This leads to more expensive cooling bills as well. Yet another thing to factor
Imagine a 150w incandescent