At the onset of darkness on Wednesday, 2013-12-11, a combined team of experts from the Estonian Maritime Administration (EMA) and Cybernetica disembarked on a visibility testing mission from the Mõntu harbour aboard the multifunctional vessel "Sektori". Six maritime professionals from the EMA and two technical experts from Cybernetica were tasked with performing field observations of the first LED lighthouse of the new generation at the Baltic Sea to be operated at a fixed and flashing rhythmic character. The purpose of the test was to evaluate navigational signal visibility improvements achieved by application of the fixed and flashing mode of operation, and to find optimum level of fixed luminous intensity for the Sõrve lighthouse. The weather seemed to be in agreement with this activity - uncommon to Estonian mid-December conditions, rather calm seas with meteorological visibility of approximately 10 nautical miles were encountered.
Although the fixed and flashing rhythmic character for navigational light signal was introduced already in early 19'th century by Augustin-Jean Fresnel (France), described in 1881 by William Thomson (Lord Kelvin, UK) in the paper "On Lighthouse Characteristics" and listed in the International Association of Marine Aids to Navigation and Lighthouse Authorities classification (Recommendation E-110, IALA abbreviation FFl), it appears to be overlooked by vast majority of AtoN authorities, with the exception of Japan. It is easy to understand that a lighthouse cannot be visually tracked in darkness at the times when the light signal is not on - during eclipses of the rhythmic character. Keeping the lighthouse signal on between the high intensity flashes only at a fraction of the peak luminous intensity empowers the mariners with the ability to maintain continuous orientation even during such eclipses, at the cost of only modest additional power consumption. Resulting improvement of situational awareness is particularly important for high speed craft navigators that are often relying mainly on visual inputs from the bridge windows. Use of LED technology enables implementation of FFl in contemporary lighthouse systems without changes to the spectrum of the light signal. Cybernetica discovered the benefits of the fixed and flashing lights during lab experiments conducted within new product development processes and has been advocating the use of FFl rhythmic characters since 2011 internationally.
After recent upgrade of the rotating lens to a brand new omnidirectional dual LED lantern E8277.W (pdf) supplied by Cybernetica, the Sõrve lighthouse is operated with listed range of 15 nautical miles at Fl W 15s rhythmic character (one flash of white light with luminous intensity of 34 kcd and duration of 0.5s in every 15 seconds). The fixed and flashing mode of operation was implemented using two external FFL Adapters E8655 (pdf) that were inserted into the modulation signal path from the existing redundant flashers to the two independent light source circuits of the lantern in order to generate pulse width modulated (PWM) control signals with pre-configured duty cycle during the eclipses of flashing. An E8655 allows implementing F.Fl at existing installations with minimum modifications, with the precondition that the AtoN light to be controlled is able to keep pace with the fast PWM control signals for provision of luminous intensities down to 1% of the flash peak.
Employing an FFl rhythmic character at the Sõrve lighthouse is a historic milestone of such new generation light source deployment in the context of the Baltic Sea. Benefits of the FFl operation were obvious both for the observation team and the crew of the ship. It was a great emotional fulfilment for us to earn a positive comment from the seasoned captain of "Sektori", Peeter Murik: "Developers of such technology deserve a deep bow".
The Sõrve lighthouse will start operating using a fixed and flashing rhythmic character in January 2014, after the international notification on changes has taken effect. Several other aid to navigation lights at the Estonian coast are expected to change to FFL within 2014.
