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FW: DIY light questions--followup

I finally got my home-built light fixture "on line" and I thought I'd share
my experiences with the list. (This may be mundane for the more experienced,
but perhaps some will find it useful.)

I built this setup for a 45 gal tank (36L x 24H x 12W) using a Motorola
"Silver Edition" 4-lamp electronic ballast and four GE F25T8 SPX41 lamps. In
my initial post to this list I asked about possible EMI and whether any
shielding would be necessary around the wires or ballast. I'm now able to
report that EMI is not a problem. I tested for this by setting up the system
on a board and plugging it in next to a TV, a stereo and a computer. None of
these showed any sign of interference from the setup. The TV and VCR also
showed no interference problems with the IR remotes (another problem I've
seen mentioned).

An issue which later came to mind was that of heat inside the light fixture.
Because my housing is nothing more than a 5" x 6" x 36" enclosed plywood
box, I was concerned that a cooling fan might be needed, or that perhaps the
ballast would need to be mounted externally. The ballast spec page says the
"maximum case temperature" is 70C (155F), and it was also brought to my
attention that flourescent lamps work most efficiently at a specific design
temp (thanks to Wade Shimona). I was more concerned with ballast life than
efficiency, but I decided to measure the heat generated by the lamps by
placing a plastic bag over them and then covering this with a dark colored
bath towel. Using a cooking thermometer, the highest temperature I could
achieve inside the plastic was about 130F, and this was at the surface of
the lamps. I therefore have not used a cooling fan and have placed the
ballast inside the housing. The temperature inside the housing peaks at
about 105F. I do have an aluminum reflector between the lamps and the
ballast, however, so this probably helps to keep the temps down inside the
housing by deflecting some heat towards the water. Also, there is no glass
between the lamps and the water, so no doubt this allows some air
circulation around the bulbs. The lights do raise the tamperature of the
water 1-2 degrees F, so I haven't yet ruled out a cooling fan for possibly
reducing this effect.

I'm very pleased with the light's function so far, even if it's not exactly
an engineering marvel. :D  Most of the plants are now producing many streams
of bubbles from their leaves, which never occurred with the Perfecto hood
and 20W 24" Vitalite I was previously using (duh). The light appears to look
fairly natural as well, even though the SPX41s supposedly have a CRI of
about 85 (anyone have a source for specs on GE bulbs?). I plan to try a mix
of plant bulbs and C50s, based on another list member's experience (thanks
to Ivo Busko for this suggestion). Anyone know if the C50s come in a 36" T8?
Any other 36" bulb suggestions?

All in all, my first attempt at DIY lights was fun and educational. If
anyone is building their own lights and wants more details on my experience,
feel free to email me.

Dan Dixon