Re: [sdiy] high output LED question - somewhat OT

[Roman]

with 6mA you wouldn't get a blasting light with anything. Even with 100% efficiency it's only 30mW of light. Multi candela LEDs usually take 50-100mA to achieve advertised brightness. Not to mention Luxeon with nominal current of 0.5A AFAIR.
So I'd suggest adding some DC/DC converter to get more voltage from the battery. Sure it may work for half an hour instead of full night, but you'll get what you want. There are special converters for this, small single chip with little extra components. Search for "white LED drivers".

Roman

---- Wiadomość Oryginalna ----
Od: "J. Larry Hendry" <jlarryh at iquest.net>
Do: Synth-DIY <synth-diy at dropmix.xs4all.nl>
Data: Mon, 5 Sep 2005 17:46:14 -0500
Temat: [sdiy] high output LED question - somewhat OT

> I need to draw on the expertise of anyone in the group concerning LEDs.  OT,
> cause it is not actually a synth project.  But, it is DIY.
> 
> I have some of those solar powered walk lights that charge up the batteries
> by day and discharge by night.  trouble is, the LED is just not bright
> enough.  I opened it up and found a quite simple circuit using a transistor
> to turn on the LED biased by another which keeps it off when there is
> sufficient voltage from the solar cells (which must mean daylight).  The
> battery voltage is abut 2.4 volts fully charged.  And that will delver about
> 6 mA into the LED.
> 
> The current flow path through the LED has no resistance.  Only the junctions
> and internal battery impedance limit the current flow.  So, I really have no
> way to increase the current to the LED other than starting over with the
> circuit (higher voltage, more cells, etc.)  I'm not going there.
> 
> So, to accomplish my goal of more light, I wish to replace the existing LED
> with one that is much more efficient in the amount of light produced for
> that mount of current.  I'm headed off to Mouser to search through LED specs
> and see if I can learning anything.  Any suggestions concerning LED
> selection criteria would be greatly appreciated.
> 
> Larry Hendry (would rather be working on my synth than this particular
> "honey-do")
> 
> 
>