I need to make LEDS brighter

Reply to Thread

I need to make some hyperbright/superbright LEDs even brighter.

Under steady state conditions they draw about 20mA at 3.6v. I
understand that they can be pulsed at a higher voltage for additional
brightness without reducing their life expectancy. In fact, I have
heard that their life can be extended because the diode junction
actually runs cooler under pulsed conditions. Does anybody know the
optimum voltage, frequency and duty cycle to use?

I understand that white LEDs are really blue LEDs with a phosphor
coating on the inside of the bottle and these cannot be pulsed above
about 5kHz, because although the LED can flash much faster, the
phosphor cannot keep up and the LEDs change colour.

Can anybody offer any help?

 

Pulsing any light source, including LEDs, does NOT make the average
light level higher for the same average power input - unless there is
some characteristic of the source that makes them fundamentally more
efficient at higher current. You cannot fool Mother Nature.

It doesn't matter -- see above.

 

Ok well I was looking for something else but I was able to find spec
sheets on your type of LED's(ie. InGaN) and they recommend 30% duty
cycle and 1kHz and 100mA of current. But I also found the math
calculation's to consider anyways.
Also found simple power supply design
Recommended power supply DESIGN for LED's will take into account for
temperature.

http://literature.agilent.com/litweb/pdf/5989-0461EN.pdf
http://literature.agilent.com/litweb/pdf/5091-9704E.pdf
http://literature.agilent.com/litweb/pdf/5963-7544E.pdf
Products homepage
http://www.semiconductor.agilent.co...fijdio.0&sProdNum=HLMP-CW38-SV000&Section=LED

 

Mentions max. recommended peak and max. recommended average currents and
ratio of these works out to pulsing at 30% dusty cycle. However, I am
familiar with this sort of LED and when the instantaneous current is
around 5 mA or more, you usually get more light from a given average
current with steady DC rather than pulsed operation.

Shows efficiency peaking at 20-30 mA instantaneous current for the LED
types in question (obvious to me other than InGaN types, probably GaP,
GaAlP or InGaAlP or the like. A major clue is forward voltage as a
function of current. InGaN is different by having maximum efficiency at
lower currents.)

This is a temperature compensation circuit. I did not see any claims of
efficiency improvement from pulsing, especially for average current around
"typical" or "maximum" of any LED type or even of any common
sort/kind/type/whatever.

Homepage for that manufacturer's products, with no claims anywhere in nor
linked therefrom that any of their LEDs have significantly better luminous
efficacy when pulsed than when fed steady DC when the average current is
at "typical"/"characterized" level or at maximum level or anywhere in
between.

More on the truths and myths of pulsing LEDs for better luminous
efficacy is at:

http://www.misty.com/~don/ledp.html

- Don Klipstein (http://www.misty.com/~don/ledp.html

 

Oh I personally would make my life simple and would power the LEDs to
the manufactures recommendations and would just bias them using
15-20mA. However if I needed to save power and wanted light I would
then pulse the LED's. No manufacture claims more light by pulsing for
the human eye. However, the human eye can't see when and LED's is on
or off when plus greater than 60Hz 50% duty cycle min . It's a
trick to save power. Not to make LEDs brighter for human eye. I was
just searching for one thing and found the specs that might help out
the original post and should have said it was impossible with out
damaging the LED.

 

Why not just lower the current to save power? Pulsing does not save
power for the same average light level unless the LED is more
efficient at the higher pulse currents. See the discussion on Don's
Web site, as listed in his message.

 

Victor, you really should know better!
Once someone believes that waggling around with the supply to an led confers
some magical power saving properties due to the human eyes characteristics
and/or special (secret?) properties of the leds, you are *never* going to
change their mind.

But then again,maybe it is best to keep trying.....

 

On Mon, 9 Feb 2004 21:51:37 -0000, "R.Lewis" <h.lewis-not this

You are, sadly, correct.

 

Victor, you really should know better!

Thanks for correcting me.

 

Its weird how tenacious this LED pulsing myth is.

Regards, NT

 

Isn't that true of all myths

 

You would be surprised at the number of products I have experienced that
modulate the current to promote efficacy/increased output.
Some of the reasons (explanations), from serious 'engineers', are quite as
bizarre as the implementations thereby produced.

It does, however, help pay the bills.

 

I need to make some hyperbright/superbright LEDs even brighter.It sort of sounds like you already have the LEDs. If that's the case
you are limited to whatever current you can push through them until
the smoke test fails and all the smoke is released.

In fact, you should be able to heat sink the little buggers and crank
50 ma through them. The traditional 3mm and 5mm bullet packs are the
WORST for this sort of treatment. Several packagers, like Microsemi
and Lumileds make SMD and DIP packages that will dissipate the
junction heat much better than the polycarb bullets, and which
therefore can handle more juice.

As far as pulsing is concerned.... Any diode will let you bang on it
really hard once or twice. But if you pulse them at frequencies high
enough that the eye sees the light as continuous (above about 50 Hz)
the LED's junction temp will be a function of the integral of the
current over time and will be the same for pulsed and DC. So unless
you are building a strobe flash or a bike headlight flashing at about
0.5 Hz, don't bother with pulsed DC.

And here is another piece of bad news. LED output decreases with age
on a curve that is roughly proportional to hours * mean junction temp.
If you run the LED hotter, it will dim faster.

 

Why not use 1W, 3W, or 5W LEDs from www.luxeon.com instead of the 0.072W
LEDs that you
are using?

 

Is that true for other colours as well as whites?

Regards, NT

 

Yes.