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'UK Display exhibition.'
1997\11\23@135829 by johnb

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I visited the exhibition at Sandown (subject of recent message), looking
for white LEDs and other very bright devices. Very little in the LED
line, but there is a lot happening; new materials such as Indium Gallium
Aluminium Phosphide were shown.

One clear trend is the increasing use of electroluminescent panels,
normally only seen as backlighting in Laptop LCDs. Some of these were
displayed at a brightness level that was actually dazzling. And, of
course, perfectly white.

It made me think - why wait for white LEDs? Very small fluorescent tubes
are available now, are more efficient than incandescent lamps, and have
a long life.

The smallest tube available seems to be 150mm (6 inches) long and rated
at 4 watts. There is one in the Maplin catalogue; since it only costs
UKP 5 (8$), I bought one.

Size is 160 x 40 x 38mm. It runs on 4 AA cells, and takes 0.4 amps, so
the wattage is 6 x 0.4 = 2.4 watts. The 4 watt tube is therefore
under-run. These tubes need a high voltage, so the 6 volts DC is
"chopped" into AC by a transistor, and then stepped-up with a small
transformer. Inside, there is about 60 pence (1$) worth of parts. It is
very cheaply done, with no attempt at regulation (there could be, with
better electronics); the tube starts glowing with a 3-volt supply, and
gets brighter as the voltage increases; I stopped testing at 7.5 volts.

Getting a focussed beam from this tube wouldn't be easy, but something
like the Maplin device is attractive if you just want to be seen in town
at night. I was nearly killed the other evening, as someone overtook in
a stupid place, and drove, on the wrong side of the road, straight at
me. I had to jump out of the way, very quickly. I don't believe he saw
me.

A workable scheme would be a pair of these lamps, (the rear one with a
red filter), powered by 6 volts worth of NiCad or lead-acid rechargeable
cells. The dynamo could then be used simply as an emergency charger.

John Blackburn,
South London UK.

1997\11\23@210931 by Ram Krishnan

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face
John,

       What was the largest size of white EL panel you saw ? I was wondering if
it would be suitable for a compact slide viewer I was planning to build.
RK

1997\11\23@213733 by William Chops Westfield

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   It made me think - why wait for white LEDs? Very small fluorescent tubes
   are available now, are more efficient than incandescent lamps, and have
   a long life.

They're high voltage devices, and not at all directional, though, leaving
them out of some applications where LEDs would be especially suitable.
There's a web page somewhere that opines that the brightest white LED
currently available is only as part of one of those "keychain" lights (sold
by gateway and perhaps others.)


   The smallest tube available seems to be 150mm (6 inches) long and rated
   at 4 watts. There is one in the Maplin catalogue; since it only costs
   UKP 5 (8$), I bought one.

Those are commercial fluorescents aimed at lighting.  There are smaller
"cold cathod fluorescent lights" aimed at backlighting in laptops and
such.  A typical tube is about 1/8 inch diameter, and can range from 1
inch to about 8 inches long (the longer ones look very fragile.)  You
can sometimes find similar lamps intended for solar-powered lawn lights
and such - it's not cheap anymore, though...


   Size is 160 x 40 x 38mm. It runs on 4 AA cells, and takes 0.4 amps, so
   the wattage is 6 x 0.4 = 2.4 watts. The 4 watt tube is therefore
   under-run. These tubes need a high voltage, so the 6 volts DC is
   "chopped" into AC by a transistor, and then stepped-up with a small
   transformer. Inside, there is about 60 pence (1$) worth of parts. It is
   very cheaply done, with no attempt at regulation (there could be, with
   better electronics); the tube starts glowing with a 3-volt supply, and
   gets brighter as the voltage increases; I stopped testing at 7.5 volts.

Thanks to laptops, there's a lot of interest in high efficiency power
supplies for CCFL tubes, with dimming capabilities and so on.  Check out
Linear Technology's web page - they think they have assorted patents on some
of the technology.

The tiny AMLCD screens that hit the surplus market over here a couple months
back came with equally tiny CCFL backlights (about 1x1x.5 inch) - designed
to run off 5V if provided with a periodic 15 uS pulse or somesuch if I read
the skimpy datasheet right (ie they contained a power mosfet and a big
inductor.)  My immediate reaction was to drive them with a PIC (actually a
basic stamp), since that's about the most convenient "pulse generator" I've
got...  (there!  Now it's PIC related!)

BillW

1997\11\24@024550 by Leon Heller

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In message <spam_OUT3478E7C3.1FBCTakeThisOuTspamdircon.co.uk>, john blackburn
<.....johnbKILLspamspam@spam@DIRCON.CO.UK> writes
>I visited the exhibition at Sandown (subject of recent message), looking
>for white LEDs and other very bright devices. Very little in the LED
>line, but there is a lot happening; new materials such as Indium Gallium
>Aluminium Phosphide were shown.

[deleted]

Maplin has white LEDS in stock. They are expensive: ~#5.

Leon
--
Leon Heller: leonspamKILLspamlfheller.demon.co.uk http://www.lfheller.demon.co.uk
Amateur Radio Callsign G1HSM    Tel: +44 (0) 118 947 1424
See http://www.lfheller.demon.co.uk/rcm.htm for details of a
low-cost reconfigurable computing module using the XC6216 FPGA

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