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Re: high pressure sodium lights

>I have been reading you folks for a few weeks, and I have learned from and
>enjoyed a great deal. Would any or all of you comment on the use of high
>pressure sodium lighting. I looked in the krib, but I found only one mixed
>comment- seemed to grow plants but over heated the fish room so the writer
>opted for a low watt flourescent setup. The ones I have been offered came
>from a horticultural operation and  360 watt lamps (new) with a corresponding
>4oo watt ballast.   Ernie D.

As previously mentioned you can get conversion bulbs to use with your 
fixtures, but these bulbs tend to be much more expensive than regular MH 
lamps. It may be cheaper to get a real MH ballast and retrofit your fixture 
(the ballasts for MH and HPS are usually the same physical size and use the 
same type of mounting). Commercial electrical supply houses have the 
ballasts at very reasonable prices (I get 175w MH ballasts, Advance brand, 
for about $17-19 or so locally -- and that's for the kit with the ignitor 
and mounting, 400w ballasts should be in the $30-40 range, but it's been a 
while since I bought such a large one). The ballast replacement is very 
easy and is explained in the instructions that come with the ballast kit.

HPS lamps will not look very good over a tank. They are a primarily 
red-yellow light (not as bad as the low pressure lights used in parking 
structures, but close). You will see many horticultural fixtures that use 
an MH bulb in combination with an HPS bulb in the same fixture to provide a 
more balanced spectrum (MH has a lot of blue). Typically HPS bulbs are used 
to supplement natural sunlight (for greenhouses), and MH bulbs are used 
where they will be the sole source of light.