I was standing on Yonah today (W4G/NG-048) and it was so clear I could see the outline of the tower and catwalk on Brasstown Bald (W4G/NG-001) 17 miles distant and it occurred to me how cool it would be to have an optical QSO from one to the other via Morse.
Would that be legal for a summit to summit? I mean visible light IS part of the spectrum, right?
If this isn’t legal it needs to be fixed so it is, because I can think of very few things cooler than this idea in our world of summits.
Legal if the decoding is done by electronic means as i understand it (ie not by eye). I think thats from another set of rules though so happy to be over ruled.
I was on a summit in VK3 doing a S2S with another group on a summit. They asked where we were, said if they look to the W they will see us on the next hill and we are waving at you. Ah, over there they said. Its in the log, the RF was done on 2m
General Rules
3.7.1 Criteria for a valid Expedition
Anybody can look at a summit from another summit.
If this isn’t legal it needs to be fixed so it is, because I can think of very few things cooler than this idea in our world of summits.
What would be really cool and within the terms of a ham licence, if you built a laser TX, modulated the laser with your information, built a laser RX and received the information.
Ahoi!
A telescope and two flags would be simpler!
You don’t need a licence for infra-red or visible light QSOs so they’re not on “amateur bands”. A shame because there’s lots of design examples of LED or LASER “radios”. Also, there were the cloud-bounce articles in DUBUS a few years back for optical non-LOS paths.
Is this the equivalent of AM? 
Admiralty messaging?
Light contacts are allowed in the ARRL VHF+ contests:
1.10. Above 300 GHz, contacts are permitted for contest credit only between licensed amateurs using mono-chromatic signal sources (for example, laser and LED) and employing at least one stage of electronic detection on receive. Laser usage is restricted to ANSI Z136 Class I, II, IIa, and IIIa (i.e.; output power is less than 5 mW).
And the ARRL also says amateurs are permitted to use all frequencies above 300GHz, which to me implies you can treat light as a ham band (at least in the US).
I once called a Royal Marine troupe up at a distance of about one mile from the hill I was on using morse sent with a small aldis lamp They were spotting for Naval Gunfire Support when I was in the Royal Navy. (don’t ask why an RN operator was up a hill).
Most people also think that light signals are strictly line of site. I remember once we were in company with another frigate, which had disappeared over the horizon. They didn’t appear to be answering CH16 either so the leading signalman turned one of the 20" carbon arc search/signal lights on and flashed it on the cloud base and successfully signalled the other ship who also replied by illuminating the underneath of the cloud using morse in the same way.
I’m sure the UK rules were similar but now they are regulated to 3THz. Above that they are not regulated and so are not amateur bands.
I had a cross band QSO from Ailsa Craig using a mirror reflecting the sun and a 2m handheld over the 10 miles back to Girvan. Logged it too. My signal was a bit shoogly but was received and understood fine.
I always carry my wee signaling mirror on the hills, measures about 1x1.5 inches and made from metal.
My light contact was made with my porch light and the blinker light on the aircraft carrier Hornet, located in San Francisco Bay, and QSL cards were exchanged. See below. Licensed hams on both ends, back when my call was Kilo Six Industrial Light Magic. The contact was written-up in QST magazine on the twentieth anniversary of that event. Note that he gave me a signal report of five by dim.
Elliott, K6EL
GW0VMW on GW/NW-064 signaling to myself on GW/NW-072 Bardsey Island. You can just make out my light in the distance. Summit claimed using 70cm FM.
Ah, but were you using morse code to signal?
We were trying!
Its really difficult just using a mirror - as you probably discovered.
Military heliographs need careful setting up to obtain a stationary angle between sun and the object you are trying to communicate with. Probably why they were not used by navies !