light ?

I don't think that's something I would do.

 

From what I've read the only thing this will do is cause algae problems.

 

i don't think it's a great idea but it can work......how much is the kelvin rating on the hid and where are you going to mount them? just because they run cooler on a car it doesn't mean it won't burn your house down.....a car is made of metal and your going to add it to a wood hood right?
i would try it as long as it has a decent kelvin rating of about 10,000k's.

 

i say go for it and see what happens....the worst it can do is heat up your water too much, bleach out corals and burn them....oh and keep an eye out on how much heat it creates in your hood......

 

I would strongly recommend not trying this on your tank if your running acrylic (people have softened/melted the euro bracing and walls with inappropriate light on acrylic)... also may need to be mindful of harmful UV (both for you and your inhabitants) depending on the light because it's not being filtered through glass/plastic shields of normal headlight or aquatic fixtures.

The kelvin rating only rates the average color temperature of the bulb, not the individual spikes and concentrations of the spectrum... hence two 10k bulbs of a specific kelvin, wattage, and PAR output causing VERY different reactions in the same coral (also why non-aquarium bulbs typically aren't used - they are only tuned to a kelvin not also specific concentrations covering a full spectrum)

It sounds like a cool experiment though - if you get gear for measuring spectrum concentrations and par ratings, have an extra rig to test with and have the time/money to invest trying out various non-aquatic HID's for successful reef keeping, many budget-conscious folk would be grateful for your results ;-)

 

I have tried different setups and measured PAR of Car's HIDs,regular MH (street lighting), and others, only to find the the radiation is not enough to be on the ballpark to induce zooxanthellae to reproduce and create "energy". The problem seems to be not only on the PAR, but as lostanime mentioned the nanometer readings for spectrum of the light peaked on the lower 200, 300 nm, range, which for certain corals is great but the cons far outweighted the cons and cause a little to low usage for our applications. The UV radiation though it's much less than that of an HQI bulb, and this would allow you to use this bulbs without a filter. Perhaps as a lux increase to the looks of your tank would be a good idea, but not for long hours a day, since inevitably will lead to algae issues faster than with an aquarium specific bulb. regular mogul base or HQI