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Re: Mercury Vapor Lights

>From: JOlson8590 at aol_com
>
>Olga in Vancouver asks about Mercury Vapor lights.  Mercury is a "Halide."
> However, MV lamps are typically Mercury Vapor Lamps, which get the light
>from an arc in a Mercury Vapor.  They have a VERY narrow spectrum of
emitted
>light. It is a very poor match for chlorophyll's needs. As a quick
>experiment, take a bright colored object under a MV lamp. (A child's toy
is a
>good example.) It will look WEIRD, because many of the colors will not be
>able to reflect the MV light.  High Pressure Sodium would be better - NOT
>GOOD - but better, as they have a much wider spectrum. "Mostly" orange, as
I
>recall.

This is correct up to this point.

>Our "Metal Halide" lamps work on a different principle: The Halide Vapor
is a
>"preservative" for a tungsten filament, a filament similar to the one in
the
>common light bulb.  However, because of the Halide Vapor protecting the
>filament, the filament can get a LOT hotter without burning out. Thus, the
>high CRI from the very HOT Filament. Also greater Lumens per Watt, same
>reason.

This is entirely incorrect.  You're confusing Metal Halide lamps with
Halogen lamps.  The tungsten halogen lamps work in the manner described
above.  

Metal Halide lamps work on the same principle that Mercury Vapor, Sodium,
and Flourescent lamps work on.  MV and Sodium lamps release light in the
visible spectrum as the plasma inside (caused by the arc in the bulb) drops
from a higher energy state to a lower energy state.  Fluorescent lamps
release ultraviolet light which hits a coating of phosphors on the inside
of the tube, causing them to glow in the visible range.  The big
differences between MH, MV, and Na lighting are the spectrum produced, the
resistance across the lamp, and the power consumed by the lamp to produce
its spectrum.  Different ballasts are required for MH lamps than for MV or
Na lamps because of these differences.

David W. Webb           Enterprise Computing
Texas Instruments Inc.  Dallas, TX USA
(972) 575-3443 (voice)  MSGID:       DAWB
(972) 575-4853 (fax)    Internet:    dwebb at ti_com
(972) 581-2380 (pager)  Text Pager:  dwebb at ti_com Subj:PAGE