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.