07-25-2010, 12:22 AM
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It is not the watts that is the problem, it is the light itself.
First, watts is a measure of energy used by a bulb or tube to produce the light, it has no direct bearing on the light's brightness (intensity). The lumens determines that, and the kelvin (the "colour" temperature) is also involved.
Over a 29g tank the single tube fixture it comes with (the hood) will suffice but only with the proper type of tube. Tubes produce various types of light called colours, rated with the kelvin scale. The sun at mid-day is around 6400K (K= kelvin) so a "daylight" or "full spectrum" tube will be around 6500K. This is the best light for a single tube fixture. You can buy expensive tubes at fish stores, or you can buy a tube at the hardware store that is just as good--provided it is full spectrum/daylight with around 6500K. These type of tubes have a higher lumen output and are therefore more intense than warm white tubes (with a lower K number) and incandescent bulbs. You can read about the colours and their significance to plants in Part 4 of the series "A Basic Approach to the Natural Planted Aquarium" which is "stickied" at the top of the Aquarium Plants section of this forum.
All standard (T8 which refers to the tube diameter) tubes in a certain length are the same wattage. However, some manufacturers now use special coatings inside the tube to create more light with less energy, so the watts may be lower. But as long as the spectrum is what I suggested, this is not significant.
As for the tube that came with your fixture it is useless. I use All Glass fixtures myself, I consider them very well made; bought two new ones last year to replace old ones that gave out, and the tubes went straight to recycling. They are purplish in hue because they have red and blue but little or no green to balance. They are also low intensity, half the intensity of full spectrum.
Phillips, Sylvania, GE all make "daylight" or similarly-named tubes that are full spectrum around 6500K. They are fine. Or you can use the more expensive tubes like Life-Glo (6700K) and ZooMed Ultra Sun (6500K). As long as they are T8 they will fit your fixture. Measure the tube itself from end to end [not the fixture or tank] as that is the tube "size".