Is it possible to dim LED christmas lights?

[Don Klipstein]

It is not posible to dim LEDs with PWM as peak current in them
remains same and
due to persistance of vision intensity appears same. Though current may
be less.

The myth persists, and this is as bad as I ever heard it!

Meanwhile, I have more on:

http://ww.misty.com/~don/ledp.html about pulsing LEDs to increase ratio of
perceived output to average current (while appearing to glow
continuously), when this works, when this does not, and how little human
vision has to do with it when it does work!

Only constant current regulation can do the job.

PWM is a common way to dim LEDs in RGB displays. Many manufacturers
recommend PWM because LED output and color as a function of varying
current can vary from one unit to another even when different units
perform the same at "characterization current", and some LEDs normally
have color varying with current.

- Don Klipstein ([email protected])

 

[psdayama]

That's not true.

Assume an LED with 20 mA through it all the time. It will exhibit a
certain brightness. Now, still with 20 mA through it, PWM it so
it's only on for half the time but with a PRF high enough so that
you can't detect any flicker. It will appear to be half as bright
as before.
JF

YES IT IS TRUE!!!!!
First U dont know anything about LEDs. At 20mA normal LEDs will blow
up soon.
But U can get the same intensity of LED with oulsing 20mA current with
25% duty
cycle. Thats called PWM. It is not PWM of voltage which will not work.
But there
are ckts which can be current controllers. Now most of the LCD displays
have
also background LEDs pulsed current so they consume less power but
dispaly
is same. Above PRF of 100 persistance of vision works which shows LED
bright
as if consuming high current.
Pls go to some wikipedia or some sites of LED manufacturers and U will
know.
Ignorance is greatest bliss !!!!

 

[jasen]

YES IT IS TRUE!!!!!
First U dont know anything about LEDs. At 20mA normal LEDs will blow
up soon.

20mA is fine for normal leds.

But U can get the same intensity of LED with oulsing 20mA current with
25% duty cycle.

BULLSHIT! try it.

Thats called PWM. It is not PWM of voltage which will not work.

that's just nonsense.

But there are ckts which can be current controllers.

resistors work great for LEDs.

Bye.
Jasen

 

[psdayama]

Oops...

Joules per second.

It is the paradox of vision.
Ur eye cant detect fast changing intensities and due to persistance of
vision
it appears as bright as if 100% lumens out.
As per Ur theory the whole new led lamps will go out of business as 3W
high
efficiency LED shines as if 40W GSL lamp. It doesnt consume that much
power
to give that Lumens.
Shallow waters make biggest noise!

 

[Frithiof Andreas Jensen]

LED's are binary devices - either ON or OFF. They cannot be dimmed in
the usual sense.

Sure they can: The light output is proportional to the current through them

 

[edegner]

Easy way to dim LED christmas lights... Plug them into an X10 outlet
that is turned OFF. When an X10 outlet is turned off it is still
putting out about 60 volts (I checked over a dozen different types of
X10 outlet, in-wall type as well as plug-in type, and they all put out
around 60 volts). Might be a little TOO dim though.

I'm trying to talk my friend into converting his display to all LED's,
but he doesn't like the way they look. Check out his display at
http://www.thatchristmashouse.com and tell me what you think.

 

[JeffM]

When an X10 outlet is turned off it is still putting out about 60 volts
(I checked over a dozen different types of X10 outlet,
in-wall type as well as plug-in type,
and they all put out around 60 volts).

Try it with a load that is more meaningful than just a 10Mohm
voltmeter.