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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.

George.

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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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