[rossb]

Dresden..
There is much to be said about lighting. From my research one should consider two things. The first is the lumens per watt and the second is the color temperature.
On the first point (lumens per watt) there is much to learn. Basically the scale goes something like this. Incandesant (includes halogen) 15-25 lumens per watt, fluoresent (no) 45, compact fluorescent (CF) 70ish, metal halide 89ish and finally sodium high pressure ...around 100. Of course these figures vary greatly. this is rather a scale of brightness.

The second and equally important is the color temperature. Without discussing like Plancs constant or other ugly concepts, one should think of heating metal...as you heat it it gets hotter and as the temperature goes up it turns whiter, which is sort of the color. As an example consider the light at the equator. At the equator at noon the equivalent light temperature is about 6500 K...but at full spectrum. When the light hits the water the longer wave lengths are filtered out and at various depths the color changes. So some marine critters like 6500K and other like the shorterwave length lights ...10,000K or at greater depths 20,000K.

If your still awake here this has a bit to do with your original question. The halogen light, although a great deal, has "yellow" light or very low light temperature. This is a light that is kind to the human light spectrum but not the reef...live rock...marine criter spectrum. As you move into the flourescent and MH bulbs you can specify the color...and hence the enviroment marine things need.

Marine critters need specific colors of light. If they don't get it ... well they croak. So in setting up your reef lighting you have to consider this. Although cheap works for humans...well...

Think of it this way, its like american beer ..its cheap, no one will argue it doesn't look like beer... you can drink that stuff all night...and all that happen is you pee alot... (no offence intended BTW)