[NewCandle] SEC - Strategic Erg Command

[Nick Reiter]

Hi Jones,

No, the spec sheet does not necessarily lie, but the
key I think is to keep in mind that the voltage
dropped across an LED changes with current!  I
mentioned this in my last e-mail on the topic.  The
figures cited by the mfg are predicated and based on
operation at 20mA!  Of course, 20mA is blindingly
bright.  But even at 1mA, the green LEDs are bright,
and at .125mA they are of a brightness similar to what
I am seeing in many of the experimenter photos!  My
guess is that at 20mA, the mean greenies might well
drop 3 volts each.

I trust the small d'Arsonval meter in series with the
LEDs... first of all, its a simple device that is
insensitive to RFI, and secondly, its on the output
side of the AV plug.

So my premise for now is that the current people think
is going through their LEDs is greater than actual in
many cases.  You can light an LED with a few
micro-amps... thats why I keep stressing 2 points -
LED photo-output may be linear with current, but power
dissipation is not necessarily linear (changing Vfwd),
and the eye lies!

N
--- Jones Beene <jonesb9 at pacbell.net> wrote:

> Nick
> 
> > The LED string I have consists of 20 green GaN
> (with
> > an average voltage drop of 2.6V at .125mA) 20 white
> GaN
> > (with an average voltage drop of 3.1V@ .125mA) and
> 18
> > orange GaAsPN (with an average voltage drop of
> 1.3V@
> > .125mA)
> 
> What am I missing here? Your figures are way-way off
> from specs. Are 
> they taken from actual measurement? If so, then is
> this measurement 
> taken using RF instead of DC ?
> 
> Here is the spec sheet for similar bulbs:
> 
> http://www.lumitex.com/tn_2-1.html
> 
> This spec sheet indicates a DC power draw of 120 mW
> per bulb, which 
> should end up for 60 bulbs being many watts, in fact
> it would be a 
> factor of several hundred times your numbers.
> 
> > If I consider the power dissipated by each LED as
> > being ~ V x A, and then add all the devices
> together,
> > I come up with a total power dissipation of
> .0176W, or
> > 17.6mW.  The eye wants to tell us that there is so
> > much more!  But eyes lie...
> 
> OK I think you can see why I am having a problem
> here assimilating these 
> numbers into the manufacturer's spec sheet for DC
> operation of the 
> bulbs. Does the spec sheet lie?
> 
> Can you please "enlighten" me ?
> 
> Jones
> 
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> 


The Holy Grail 'neath ancient Roslin waits.
The blade and chalice guarding o'er Her gates. 
Adorned in the masters' loving art, She lies;
She rests at last beneath the starry skies.


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