# Seeing the light of Morse

Both yargo and katolaz submitted articles dealing to some extent with Morse code
to this issue of Circumlunar Transmissions.  After reading them both in my
capacity as editor of this issue, I felt compelled to make a small contribution
of my own in the hopes of rounding this theme out a little.  The other two
articles focus mainly on the use of Morse code in the context of radio.  This
makes perfect sense, as amateur radio is in some sense the "natural habitat" of
Morse code in the 21st century (and, of course, both the authors are licensed
amateur radio operators).  However, as yargo mentioned, the code itself is
largely independent of medium and can be transmitted using any system which
offers control over the duration for which any two distinct "symbols" are
present.  Probably the second most frequent medium in which Morse code has been
used, after radio, is light.

Instead of transmitting a radio carrier or generating an audible tone, one can
simply turn on any source of visible light, and leave it on for the appropriate
duration before turning it off again.  Particularly at night time, the flashing
light can be seen over long distances, especially if binoculars or a telescope
are used.  Not as long as a high frequency radio signal bouncing off the
ionosphere can travel, of course, but longer than a shout (or a whistle) can be
heard.

Using visible light to send communications using Morse code has a long history,
especially in military contexts, dating back to at least the 19th century.  So-
called "heliographs", using a mirror to reflect the bright light of the sun and
relying on purely mechanical means to break the beam were used in both World
Wars to provide instantaneous long-distance communication without any need for
electricity or cables.  So-called "Aldis lamps" have a long tradition of use at
sea, a method pioneered by the Royal Navy.  Heliographs were also used in
civillian contexts, including the US Forestry Service.

There are two things that I find especially appealing about light-based Morse
code:

Firstly, unlike radio, there is essentially no legal barrier and greatly reduced
financial barriers to its use.  Almost every country on Earth has a complicated
system of regulation in place controlling who is allowed
to send radio communiations of given strengths on given frequencies.  Getting a
license to transmit typically involves studying for an exam and paying a regular
fee, and amateur operators are typically required to identify themselves on air
regularly and are prohibited from using encryption.  In contrast, I very much
doubt there is any country on Earth that has laws prohibiting the use of an
electric flashlight in just about any way whatsoever, and most people could
start communiating in Morse this way at the drop of a hat if they had somebody
to communicate with and a clear line-of-sight to that person, with no technical
training (aside from learning the code itself) and at negligible cost.  Building
your own equipment to improve on a flashlight is much easier and much cheaper
than building your own radio transmitter.

Secondly, it scales incredibly well with technology level, in both directions.
In a high-tech, industrialised society, the entire process could happen purely
automatically at high speed using energy efficient LEDs and highly sensitive
photodiodes connected to microcontrollers.  Automatic repeater stations could
relay signals further than the range of any individual link, perfectly analogous
to the use of radio repeaters.  On the other hand, the *exact* same system is
feasible, albeit at much lower speeds, in a purely pre-industrial society using
mirrors (which have been made since the Bronze age) during the day and oil lamps
at night.  The scheme benefits from but is in no way dependent upon various bits
of science and technology in between these two extremes, like being able to
grind magnifying lenses out of glass, or use electricity to generate light at
night time.  If you're interested in communications technology which "degrades
gracefully" in the face of natural disasters, power shortages or infrastructure
breakdowns, or even full-blown societal collapse, this is an extremely desirable
property.

Of course, optical communication is not without drawbacks: compared to radio it
is much vulnerable to having its range shortened by heavy rain, fog, smoke, or
terrain.  Communicating over plains or between mountain peaks is easy, but if
you're down in a valley it's a different story.  But for people who are
interested in more sustainable, lower-tech approaches to wireless communication,
I think it's certainly worth thinking about and experimenting with.