Here is an introduction to the metal halide technology for those interested to learn a little more:
"Metal halide lamps work on the same general principles
as fluorescent lighting, namely by passing an
electric current through a gas-filled tube via some
type of ballast. Generally, the process is known
as high-intensity discharge (HID). In this case,
the gas used is vaporized mercury, which is
supplemented by additional metal iodides such
as thallium, indium and sodium. It is the
addition of these extra elements which allows the
characteristics of the light source to be carefully
controlled.
When an electric arc is produced between the
lamp electrodes, the metallic and iodine ions are
separated, and the energized metal ions emit
visible light. The gases cool as they approach the
outer surface of the arc tube, allowing ions to
recombine and flow back towards the electric arc
by convection alone.
Although the light produced by metal halide
lamps is of high quality (i.e. it is white) and high
efficacy, this technology does have drawbacks,
which presently include lengthy restarting after a
shutdown (due to cooling requirements) and high
UV radiation levels. Their brightness also
demands specially designed fixtures.
Nevertheless, metal halide lamps offer significant
potential as a point lighting source in the next
century. An efficacy of 150 Lumens/Watt is likely
achievable by the year 2030. In comparison,
current metal halide lamps display efficacies of
90 to 105 Lumens/Watt, including the ballast.
The 35% higher efficacy would reduce connected
light loads in typical high bay applications from
current levels of 21 W/m² (2 W/ft²) to 14 W/m²
(1.3 W/ft²) in the year 2030.
Improved electronic ballasts will likely reduce
lamp size and allow instant restrike capability, as
well as improving efficacy from the present levels.
Source(s) of Information:
(1) E-Source Lighting Technology Atlas 1997, ESource,
Boulder CO.
(2) Lighting Research Center (LRC), Rensselaer
Polytechnic Institute, Troy, NY
(3)Advanced Lighting Technologies (ADLT) /
Venture Lighting International Inc.
www.adlt.com
One of my former collegue was doing research on high performance e-ballast for MH bulb. I saw one of his prototype,
which is very compact (~ 5"x2"x2"), and light weighted too (no heavy transformer, replace by high voltage solid state power electronic components) and can be dimmed between 100% to 10% without flickering. He has left the Uni now to join a company to bring the result of his research into commercial production. He told me the material cost is around ~HKD 100.
Maybe we will soon find very efficient e-ballast for MH bulb on the market. That will be good news for fish fans!
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