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    Re: Lights,Leds and scopes etc.
    From: Dave Weilacher
    Date: 2003 Oct 14, 10:24 -0400

    Hi George;
    How about looking at this site and commenting.
    I am most interested in the dual contact 15mm base bayonet replacement bulbs.
    White 19 LEDs either narrow or wide angle.
    My boat has old side and stern lights (1975) with concave reflectors built into the housing.
    Currently, I have 5-LED lights in my stern and port bow running lights.  I am 
    told that the stern light is adequate as viewed from a following boat at 
    night.  However, the port light just doesn't seem bright enough.  This may be 
    due to the red filter glass that it has to illuminate through.
    I am looking for legal as opposed to something bright enough to read by.
    -----Original Message-----
    From: George Huxtable 
    Sent: Oct 14, 2003 9:43 AM
    Subject: Re: Lights,Leds and scopes etc.
    Jared Sherman said-
    >12 LED's, typically 40mA each. That would draw 0.48 Amps,
    Comment from George-
    That's not the way anyone would drive such an array, not if he was trying
    to conserve the power taken a 12-volt power source.
    Instead, the diodes should be strung together IN SERIES, as far as
    possible. It depends somewhat on the details of the specified voltage drop
    across each LED at full output, but 4 or 5 such diodes connected in series
    should still add up to less than 10 volts, allowing a somewhat-depleted
    battery to drive them, with a bit of "headroom" for a current-regulator to
    work properly.
    Each such diode string would require a separate current regulator. If a
    12-diode array was made up of, say, 3 such strings, then the overall
    battery drain would then be only 0.12 Amps, not 0.48 Amps as Jared
    suggests. Three separate current regulators would be required in this case,
    each able to cope with dissipation about 0.2 Watts to deal with the
    enhanced voltage on the rail with a highly-charged battery and a running
    engine: this is not very demanding.
    I've made enquiries about the bicolour bow lights referred to in the website-
    , that Bill Noyce suggested.
    As far as I can tell from the picture shown, these have 6 red lamps and 6
    green ones. The suppliers tell me that they are all strung in series, which
    would require more voltage than a 12 volt battery can deliver. So they have
    to use some sort of current-stabilised switch-mode power supply for
    dc-to-dc step-up, to generate the 30 volts or so that's required. There's
    no reason why that shouldn't work, with reasonable efficiency. However, I
    have something of a bias against such oscillating power supplies in that
    unless they are very well designed they can give rise to RF interference,
    in a similar way that fluorescent lamps do. Enquiries continue.
    It appears that the 6 lamps each side must be individually angled so that
    if you are in the defined arc-of-view there will always be at least one of
    them pointing in your direction. Each diode emits light in a narrow cone,
    so the whole thing is a bit like a fly's compound eye, but working in
    reverse. It must be a matter of careful compromise to achieve the required
    illumination of the prescribed arc (112.5 degrees horizontally, ?25 degrees
    vertically for a sailboat) with the necessary sharp cutoff, using the
    minimum number of diodes.
    The colregs (or at least my copy valid in 1977, which is all I have here at
    home) require screens for sidelights to achieve "practical cut-off" of
    light between 1 and 3 degrees outside the prescribed sectors. An exception
    is made to the requirement for a screen in the case of a "combined lantern,
    using a single vertical filament and a very narrow division between the
    green and red sectors". Such filament lanterns, as we know, achieve
    excellently sharp red-green cutoff. If a LED lamp is to claim the same
    exception to the requirement for screens, I imagine it would need to show
    comparable performance. I am, as yet, unconvinced. Enquiries continue about
    that, also.
    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.
    Dave Weilacher
    .US Coast Guard licensed captain
    .    #889968
    .ASA instructor evaluator and celestial
    .    navigation instructor #990800
    .IBM AS400 RPG contract programmer

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