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    Re: Lights,Leds and scopes etc.
    From: Fred Hebard
    Date: 2003 Oct 14, 16:20 -0400

    The amount of energy in a foot candle or lumen is dependent upon the
    frequency distribution of the emitted light.  LEDs usually have a very
    narrow frequency band in which they emit light, so would be much more
    efficient than incandescent light sources (more-or-less more lumens per
    watt).
    
    Fred
    
    On Tuesday, Oct 14, 2003, at 15:50 US/Eastern, Rino van Dam wrote:
    
    > Found this on the 'Net:
    >
    > Perry's handbook of Chemical Engineering - Conversion tables 1-7
    >
    > to convert from            to          multiply by
    >
    > Candle power(spherical)  lumens          12.556
    >
    > lumens                    watts         .001496
    >
    >
    > result  .0188 watts/CP
    >
    > Rino
    >
    >
    > -----Original Message-----
    > From: Navigation Mailing List
    > [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]
    > On Behalf Of David Weilacher
    > Sent: Tuesday, October 14, 2003 15:41
    > To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    > Subject: Re: Lights,Leds and scopes etc.
    >
    >
    > Does anyone have a 'workable' (as opposed to accurate) formula for
    > converting between lumens, candlepower, and watts (lighting)?
    >
    > Is candlepower and candela synonimous?
    >
    > Is it true that a WW2 pilot could see a candle burning in a window at 8
    > miles?
    >
    >
    > -----Original Message-----
    > From: George Huxtable 
    > Sent: Oct 14, 2003 3:39 PM
    > To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    > Subject: Re: Lights,Leds and scopes etc.
    >
    > Earlier today, I sent a mailing as follows (in part)-
    >
    >> 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.
    >
    > =================
    >
    > Some of that was certainly wrong, and I would like to backtrack, with
    > some
    > apologies.
    >
    > Dave Weilacher posted-
    >
    >> How about looking at this site and commenting.
    >>
    >> http://www.superbrightleds.com/
    >
    >
    > So I did; and there found some detailed specifications for superbright
    > LED's, reg, green, and others.
    >
    > And discovered that for the green LEDs, the forward voltage drop at
    > maximum
    > output was significantly greater than I expected, between 3.5 and 4
    > volts.
    >
    > That implies that it would be quite impossible to power "4 or 5 such
    > diodes"
    > from a 12 volt supply, as I had suggested. In fact, one could
    > series-up no
    > more than two such diodes: which would still be worth doing, for
    > current
    > economy, rather than connecting them in parallel. Each  series pair
    > would
    > then need its own current driver.
    >
    > For the red diodes, the voltage drop is significantly less, and it
    > would be
    > quite practicable to connect 4 such diodes in series (but not 5), with
    > a
    > current driver.
    >
    > Sorry to get that wrong.
    >
    > In view of these higher voltage drops, the use of a current-regulated
    > power
    > supply, providing sufficient voltage step-up to drive all the diodes
    > in a
    > lamp in a single series chain (as in the "orcagreen" lamps), seems a
    > rather
    > sensible alternative.
    >
    > George.
    >
    > ================================================================
    > 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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