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post #19 of (permalink) Old 08-02-2011, 09:02 PM
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Sorry to revive this thread but I had some information I thought might be worth adding that wouldn't be worth starting a new thread for.

FWIW I have HID foglights on my car and it uses a projector lens with a cutoff shield inside the projector to project uniform light all over the ground. It would be really, really easy to open up the projector and take out the cutoff shield. Doing so would result in light that is projected at a very wide angle and fairly uniform in a circular pattern.
The following picture isn't entirely correct, as the lens is what flips the light and they seem to have illustrated light just flipping randomly, but you can see how the cutoff shield would make a shadow at the bottom of the lens.
The lens then flips this "image" and creates a shadow at the top half of the projection, this way you aren't blinding other drivers.

Removal of the shield would make what I imagine to be quite good light dispersion, better than any reflector alone could ever create, that's why projector lenses were adapted for automotive use to begin with.

Also, in an older post someone mentioned that HID ballasts aren't good at handling moisture and get very hot.

This may be true in older technology but the majority of modern aftermarket ballasts are completely waterproof, you could even submerge them and they would work.
Most of them are internally sealed with some sort of non-conductive silicone type product, thats not to say that the seals on the casing are sealed, but rather the entire circuitry is encased in silicone.

The heat of the ballast is negligible. The heat from the bulb is comparable to MH.

For anyone interested in trying this out, as someone mentioned you are getting 2 ballasts and 2 bulbs. Ballasts should last 5+ years, if you get a faulty one it will probably break within the first year and you can swap it out via warranty. The bulbs in my car have lasted 2 years but the bulbs I had before only lasted a bit over a year, so that gives you 2-4 years of use with no bulb replacements. That is assuming that they do not get worse at growing plants over time like other bulbs do.

Also the thing that makes these burn out the quickest in cars is turning them on and off multiple times a day, so running them constantly for 8 hours a day really shouldn't shorten the life compared to automotive use. I would imagine the life to be about the same for both aquarium use and automotive use.

For anyone interested in trying this, I recommend as they have good warranty claim system, have been around for quite a while and have updated their technology multiple times over the years, the current platform is probably the best you can buy, and its ridiculously cheap. The ballasts are miniscule compared to older ballasts and replacement bulbs are fairly cheap.
You could get a universal projector foglight kit off ebay, whichever one looked the nicest to you for your budget, and just rig this up to hang from the ceiling over the tank.

My only concerns are the PAR output of HID(although you can request special colored bulbs which do not have a colored filter on the glass which would reduce lumens, but instead use a different mixture of gasses in the bulb to produce different colors, but you'd be shooting in the dark as to what colors would give you better par.)
From what I've read HID lights produce a good bit of light in the "lower chlorophyll A segment of PAR" but not as much in the infrared segment.
Although you'd have 2 projectors and 2 ballasts and 2 bulbs so you could double up if you wanted.
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