LED can only absorb a certain amoung of power. Usually a resistor is
wired in series to limit the current but the resistor will eat some
power too. The formula is R = (Supply voltage - LED voltage)/LED
current (in amps) For example a 4V 25 mA LED run with 12V requires a
320 ohm resistor. ( (12-4)/.025 ) The same amount of current flows
through both the resistor and the LED but the voltage across the
resistor is twice that of the LED so the LED will use 97 mW and the
resistor will eat 194mW. YOu can put 3 or 4 LEDs is series and waste
less power but you are not going to get maximum brightness.

Also, LEDs are very directional. They may work fine for a map light but
it would take several carefully arranged LEDs per fixture to get wide
coverage.

The high power LED nav lights like Deep Creek use pulse width modulation
(a little oscillator type thingie) to blast a whole bunch of LEDs with 2
or 3 times the rated voltage but only for half to 1/3 the time so the
average power that the LED sees is within its limits. The result is
more light with less power wasted.

The main thing they have going for them is an almost infinite life
spand. From what I can gather, LEDs with high tech drivers are great
for anchor and tricolor bulbs that are on all night but with only a
small improvement in efficiency over florescents, don't seem to be cost
justified for interior lights.

bruce wrote:

hi
a workmate suggested i use LEDs instead of 12v bulbs for lighting on my
28ft yacht. i have house & engine battery and although i live aboard the
cabin lights dont get a lot of use, but nav lights are generally on all
night. has anyone had any experience with replacing conventional lighting
with LEDs? Would i need a step down transformer on the ligting circuits
because the LEDs are generally 4volt?

cheers
bruce

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
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