RE Tungsten Halogen

>I have seen some of these lights (for illuminating driveways etc) and am
>wondering "why not?" I can buy one of these units for 9 (~$15), whereas to
>equip my tank with flourescents, ballasts etc would cost me well over 100
>($150). Is there an "absolutely not" type reason?

You can use these (known as low voltage dichroics), but the standard ones
have a colour temperature that is generally considered to low for good plant
growth, around 3000K-2500K. There is a new low voltage dichroic on the 
market that has a colour temperature of 4700K, CRI 87 that is a daylight
lamp that does look very good on a planted tank. I hve seen them available 
for between AU$13-AU$20.

Marque APD - ANGFA(NSW) - Sydney