Join Date: Jan 2004
Location: Las Vegas , Nevada
Oops, I didn't realize you're in UK. Over here, power compact flourescent are the most popular for planted tank enthusiasts. I'm not sure what is over there, maybe T-5? Anyway, 14 watts bulb is a T-8. 28 watts for a 5 gl is a bit on the high side but not really overboard. The bulbs still only have the 14 watts of intensity. I use around 5 watts/gl for my 10gl (12" high).
I always mix different temp. bulbs to get a better look. If you go with 2 power glo, your plants color will look pale. The blue hue that power glo emit really wash out a lot of colors. If you just use the 6500K (I think it's sun-glo), the tank will look a bit green. Mixing the 2 will even out everything and will look more natural.
Regarding the 1.5" gap, it's not a big deal. You won't notice it.
If you go with 14watts bulb only, you'll have some problems with those high light demanding plants. The intensity is just not enough. If you're worried that the 28 watts are too much, you can raise the light fixture a bit.