From: Mike Lorrey (mlorrey@datamann.com)
Date: Fri Jul 06 2001 - 08:05:14 MDT
452CF5.25EDC97F@comp-lib.org> <OE68RZ1UbDBRArVc4Iu00013158@hotmail.com>
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Robert Coyote wrote:
>
> What about LED's?
LEDs are more efficient than compact fluorescent, however they are also
more expensive. For approximately twice the price, you save only an
additional 10-20% of the original incandescent wattage. This will likely
change over time, and there are niche applications where LEDs make a lot
of sense, like traffic lights, exit signs, floor level pathway lighting,
and personal illumination devices like book lamps, etc. Further on down
the line, Electroluminescent technology will eventually replace area
illuminate applications, but I think this will require some advances in
nanotech before such technology can provide the lifecycle needed to pay
off the increased cost. An EL lamp is essentially a flat capacitor, with
an opaque conductive back layer (usually a silver paint), a transparent
conductive front layer (usually indium/tin oxide), and a
electroluminescent doped dielectric material in the middle (typically a
complex phosphor compound). The alternating electrostatic field provided
by an alternating current stimulates the phosphor to produce light. The
problems with this lamp include a half-life-like degradation of the
phosphor compound in reaction to the ingress of moisture over time, as
well as arcing between front and back layers through flaws in the
substrate. Moisture based degradation can be mitigated by encapsulating
phosphors within material that acts as moisture barriers or dessicants,
as well as laminating the whole lamp within impermeable moisture barrier
materials while still remaining transparent enough for effective light
transmission.
EL lamps are generally produced by silk-screen printing techniques,
though there has been research in high resolution printing with more
modern processes of regulated compound deposition. This has mostly
occured in the area of using EL lamps as pixelated flat panel displays
rather than as general lighting sources. The major problems with EL for
bright illumination applications is the difficulty in concentrating
sufficient phosphors within the dielectric while keeping front and back
electrodes close enough for efficient dielectric density but far enough
to limit arc-over related failures. I expect that these problems will
only be resolved when lamps can be constructed by assemblers on an atom
by atom basis.
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