NavList:

   

Reply

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@LISTSERV.WEBKAHUNA.COM]
> On Behalf Of David Weilacher
> Sent: Tuesday, October 14, 2003 15:41
> To: NAVIGATION-L@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@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@huxtable.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
>
>

   

Reply