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    Re: Nav light colors and ranges
    From: George Huxtable
    Date: 2003 Oct 18, 22:46 +0100

    On 10 Oct Bill Noyce suggested that there was useful information on LED nav
    lights to be found on-
    I followed up his suggestion, and put some additional questions, which the
    website itself didn't clearly answer, to-
    Hobie Caldwell
    OGM Corporation
    phone: 281-535-5777
    fax: 512-233-0595
    I'm pleased to say that Hobie has been very responsive in answering my
    questions, which I will summarise below with relevant extracts from his
    answers. Mostly they refer to their LED bicolour pulpit lamp.
    I asked how the lamps were connected and powered. It appears that the bow
    array is made up from 7 red lamps and 7 greens.
    >The wide operating range of our light (down to 3V) is not an indication of
    >the internal LED connections.  We use a patent-pending step-up constant
    >current regulating circuit, which always maintains the proper current
    >through the LEDs, which are in series.  Thus, even with 3V input, the
    >will produce up to 30V to keep the LEDS in series at exactly the specified
    >brightness by maintaining a regulated current through them.  It is the
    >current and not the voltage in an LED which must be regulated.  This
    >guarantees maximum efficiency, optimal brightness, and maximum LED life
    >because the current through the LEDS is always within the recommended
    >specifications of the manufacturer.
    To me, this seems a sensible arrangement, to string the LEDs all in series
    and drive them from a current-regulating stepup supply, if no problems
    arise from RF interference emitted from that switching regulator. So I
    asked about interference.
    The answer came-
    >Regarding EMF, it is my opinion that the tiny regulator circuit will not
    >produce any harmful EMF radiation for the following reasons:
    > - the entire circuit is tiny, fitting within the size of a U.S. dime, thus
    >there are no 'antennas' to radiate electromagnetic waves;
    > - the switching frequency of the regulator is on the order of 1 MHz, which
    >has a wavelength of several meters.  Since the components are so small there
    >is no electrical path that even comes close to a quarter wavelength.  Thus
    >no antenna effect.
    > - the switching current is very small....20 mA, thus the EMF is small.
    >  We have not experienced any interference with systems
    >on any installations to date.
    >Regarding EMF, the 1 MHz frequency loop is constrained within only a few
    >components of the regulation circuit (1 capacitor, 1 diode, and the IC).
    >the current through the LEDs and from the battery bank is constant and is
    >not modulated at the high frequency. In addition, the input from the battery
    >bank is well-filtered at the light.  Therefore, you will not see harmonics
    >in the supply wires.
    I asked about immunity to surges on the 12v supply-
    >Each one of our lights has a varistor to absorb a limited amount of energy
    >spikes.  However, any spike that exceeds the absolute maximum rating of the
    >regulator chip, which is 18 VDC, will damage it.
    I asked about the light distribution pattern for their bicolour pulpit lamp.
    >The brightness of our lights remains consistently above the 2nm visibility
    >requirement at all angles required by the regulations. The cutoff angles
    >are also very good.  I'm enclosing a .jpg image that shows the intensity at all
    >angles around our bicolor bow light.  The flat line across represents the
    >minimum intensity for 2nm visibility.  The downward sloping angles show the
    >cutoff requirements.  As you can see by the bar graphs, our lights exceed
    >the 2nm visibility line, and do very well at staying below the cutoff line
    Rather than reproduce that attachment, I have extracted the information
    from the graph provided in the form of a table, where the numbers have been
    estimated from the heights of the graph, but correspond well with the bar
    graph itself.
    Red (port) LED array at 0 degrees tilt.
       angle range   Measured    Required
       from bow     brightness  brightness
          (deg)     (candela)   (candela)
        -?   to  -3    1.2         0.7
        -3   to  -1    2.3         2.4
        -1   to   0    2.7         4.3
         0   to  10    7.2         4.3
        10   to  20    7.7         4.3
        20   to  30    6.0         4.3
        30   to  40    5.4         4.3
        40   to  50    5.8         4.3
        50   to  60    5.6         4.3
        60   to  70    4.8         4.3
        70   to  80    5.4         4.3
        80   to  90    5.9         4.3
        90   to 100    4.5         4.3
       100   to 107.5  3.1         2.2
       107.5 to 112.5  1.2         2.2
       112.5 to 117.5  0.5         0.4
    Indeed, it does comply with the requirements over most of the range, with
    the odd shortfall. I wanted to know more about how completely the light
    fell off outside the specified angular range.
    Hobie Caldwell commented-
    >Regarding the cutoff angles greater than 3 degrees, the testing laboratory
    >does not test beyond the COLREGs spec of 3 to 5 degree cutoff.  However, the
    >graph does show a steep roll-off of light output from the other side beyond
    >3 degrees.  You may extrapolate the line in the graph to angles beyond 3
    >degrees.  Because of the light's design, it is well shielded from side to
    >side, thus you will not experience any peaks in light crossover beyond 3
    >degrees.  It continues to roll off rapidly.
    I asked about whether the lamps conformed to the sailboat requirement, that
    the light should not fall below 50% at tilt angles above 25 degrees.
    >I have not compiled the tabular data into graph form from the testing
    >laboratory yet for the other tilt angles.  It is on my list to do.
    I asked whether any LED arrays had received any form of type-approval from
    USCG or any other certifying authority, but that question wasn't answered.
    In summary then, my personal opinion from all this is that LED arrays are
    certainly close to being a viable replacement for straight-filament lamps,
    and may well offer a welcome factor of 10 or so reduction in power
    consumption, and very likely a longer life. But it's not yet clear, to me,
    whether they offer a fully-legal replacement just yet, and the current high
    cost is certainly a disincentive. In my view, their time is coming soon,
    but perhaps not just yet.
    contact George Huxtable by email at george---.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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