🚀 go-pugleaf

In article <523@rbdc.UUCP>, andy@rbdc.UUCP (Andy Pitts) writes:
> I want to build a light hood for a marine aquarium.  This requires intense
> light with a spectrum that closely matches the sun.  The best results seem
> to be with metal halide arc lamps.  Commercially available units sell for
> about $400.00 and use 2 175 watt lamps.

	"Marine aquarium", indeed!  Do you think that you can fool the Net
with that story?  Why, we all know that metal halide lamps are used indoors
for only ONE purpose: to grow mary-wanna!  For detailed technical information
on the indoor application of metal halide lamps, just consult any issue of
"High Times".

	:-)  [serious technical questions and answers follow]

> 1) Mercury vapor street lights can be had at very reasonable prices. Can
> you use a 175 watt metal halide lamp with a 175 watt mercury vapor ballist?

	In general, no.  Metal halide lamps, mercury vapor lamp and
high pressure sodium vapor lamps are in a category known as High Intensity
Discharge (HID) lamps  HID lamps are in effect negative resistance devices
and require current-limiting ballasts.  In addition, HID lamps require
starting voltages higher than line voltage (200 to 400 volts for metal
halide and mercury vapor; 2,500 to 3,000 volts for high pressure sodium).
	Most ballasts are wound as autotransformers, and not only provide
the necessary current-limiting, but provide a higher voltage for starting.
	In general, metal halide lamps require a HIGHER starting voltage
than mercury vapor lamps; the voltage-current characteristics of metal
halide lamps are also different than those of mercury vapor lamps.  There
is a very good possibility that an el-cheapo mercury vapor ballast will
not ignite a metal halide lamp; even if it did, the ballast may overheat
since it was never designed for metal halide use.

> 2) If not, where can you get ballists and sockets without paying an arm and
> leg?

	From a commercial electrical supply firm, such as Graybar Electric.
Price is relative, however; I don't know of any source for "bargains" in
this type of product.

> 2a) Are high frequency ballists available at reasonable prices?  If so where?

	As far as I know, no high frequency ballasts are available for HID
lamps (I don't believe there is any reason to use high frequency in this
type of application).

> 3) Can you mount these lamps in any position?

	It depends upon the particular lamp; some lamps and fixtures ARE
position-sensitive.

> 4) Is there any place where junk fixtures could be obtained cheap and the 
> ballists salvaged.

	In the grand scheme of things, metal halide lamps are comparatively
"new", as opposed to mercury vapor lamps; I would not expect to see much in
the surplus area.

> 5) What else do I need to know?

	You might wish to ask the people in alt.drugs. :-)

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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