red LEDs known as PT54 Phlatlights has arrived. These are VERY VERY bright LEDs mounted onto substantial heatsinks which emit a strong signal on 480THz. They were originally intended for portable projection systems. One of mine is going into my QRO optical beacon running continuous carrier, CW, DFCW, QRSS3 or QRSS30 to use in further over the horizon (non line-of-sight) beaconing tests using the scatter from particles in clear air and the reflection off the base of clouds. Last winter my own simple beacon running at around 300mW was detected several km over the horizon using QRSS3. G4HJW's optical beacon using a Phlatlight LED was detectable in my village some 8-9km over the horizon. In neither case could the red glow from the TX be detected by eye. This week I also received some SFH213 10 degree half angle PIN photodiodes which should be considerably more sensitive than my BPW34 detectors currently in use. Estimates suggest at least 6dB more sensitivity.
Together, the QRO optical beacon running from home, focussed with a 100mm lens (gain about 24-30dB), and a portable high sensitivity 100mm lens based detector should allow plenty of scope for innovative NLOS tests on dark winter evenings.
Just realised: 5W out (for example) into a 30dB gain lens "antenna" is equivalent to 5kW of light power in the beam. That is SOME bright light. Clearly great care is needed in siting and aiming such a system to ensure safety.