"dazed and confuzed" wrote in message
...
I believe he wants to strobe them faster than the eye can percieve.
something like 50 hz would do it.

Ah, now I understand. But this has no benefits. A LED that is continuously
on at, say 20mA, will appear to have the same brightness as when strobed
with a 20% duty-cycle (1/5 of the time) at 100mA (5 times the current).

Meindert

On Sat, 27 Nov 2004 08:03:59 +0100, "Meindert Sprang"
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

"dazed and confuzed" wrote in message
...
I believe he wants to strobe them faster than the eye can percieve.
something like 50 hz would do it.

Ah, now I understand. But this has no benefits. A LED that is continuously
on at, say 20mA, will appear to have the same brightness as when strobed
with a 20% duty-cycle (1/5 of the time) at 100mA (5 times the current).

Meindert



Actually not quite. If you talk energy consumption then you are right.
But you can viciously overdrivve LEDs to get far more brightness out
of then than they normally can give.

see:
http://www.stockeryale.com/i/leds/lit/app001.htm

There is also argument that your eye and brain think that the led is
still alight and this can fool you into seeing a brighter LED. I would
reckon this would work best for LEDs being looked _at_, rather than
thiose used as a source of illumination.

"Old Nick" wrote in message
...
Actually not quite. If you talk energy consumption then you are right.
But you can viciously overdrivve LEDs to get far more brightness out
of then than they normally can give.

see:
http://www.stockeryale.com/i/leds/lit/app001.htm

I know, I have used that principle to drive IR leds to illuminate a scenery
for the time of one frame of a video camera.

There is also argument that your eye and brain think that the led is
still alight and this can fool you into seeing a brighter LED. I would
reckon this would work best for LEDs being looked _at_, rather than
thiose used as a source of illumination.

Mmm.... I'd thought that the eye/brain combination would average it, but on
the other hand, the mind can do strange thinks. I'll might try it some day
by comparing two LEDs next to eachother, one continuously driven and the
other with a duty cycle.

Meindert

You need to do it as a blind study. Your preknowledge of which is driven
how may color your perception in something as subtle as that.

--
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"Meindert Sprang" wrote in message
...
"Old Nick" wrote in message
...
Actually not quite. If you talk energy consumption then you are right.
But you can viciously overdrivve LEDs to get far more brightness out
of then than they normally can give.

see:
http://www.stockeryale.com/i/leds/lit/app001.htm

I know, I have used that principle to drive IR leds to illuminate a
scenery
for the time of one frame of a video camera.

There is also argument that your eye and brain think that the led is
still alight and this can fool you into seeing a brighter LED. I would
reckon this would work best for LEDs being looked _at_, rather than
thiose used as a source of illumination.

Mmm.... I'd thought that the eye/brain combination would average it, but
on
the other hand, the mind can do strange thinks. I'll might try it some day
by comparing two LEDs next to eachother, one continuously driven and the
other with a duty cycle.

Meindert

On Sat, 27 Nov 2004 10:29:14 -0700, "Bob La Londe"
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

You need to do it as a blind study.

Now _that_ would be fruitless! G

Your preknowledge of which is driven
how may color your perception in something as subtle as that.

I agree however.

On Sat, 27 Nov 2004 16:21:18 +0100, "Meindert Sprang"
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

"Old Nick" wrote in message
.. .
Actually not quite. If you talk energy consumption then you are right.
But you can viciously overdrivve LEDs to get far more brightness out
of then than they normally can give.

see:
http://www.stockeryale.com/i/leds/lit/app001.htm

I know, I have used that principle to drive IR leds to illuminate a scenery
for the time of one frame of a video camera.

OK. Sorry. Then I misunderstood your argument, unless you were talking
about actual efficiency. You seemed to say that strobing had no gain.


There is also argument that your eye and brain think that the led is
still alight and this can fool you into seeing a brighter LED. I would
reckon this would work best for LEDs being looked _at_, rather than
thiose used as a source of illumination.

Mmm.... I'd thought that the eye/brain combination would average it, but on
the other hand, the mind can do strange thinks. I'll might try it some day
by comparing two LEDs next to eachother, one continuously driven and the
other with a duty cycle.

I carefully said there was "some argument" about this! G ABob says,
you need to test with extreme care.

Perceived brightness is proportional to average physical power output
of flashing light sources except for relatively low flash rates.
Above the critical flicker fusion rate (the flashing rate above which
the source does not appear to pulsate), the visual system responds
only to average power, not peak power. Consequently, there is no
perceptual advantage to pulsing LEDs at high rates. However, LEDs
themselves do not have output directly proportional to current, and
this fact can sometimes be used to improve physical power output by
pulsing. For example, if a particular LED has its highest flux output
per milliamp input at 100 milliamps, and the available current is
10mA, then the LED will have higher output pulsed 100mA with 10% duty
factor than operated with DC at 10mA. In other words, if you're
application requires operating the LED at an average current below its
point of highest efficiency, pulsing can be advantageous. On the
other hand, if you're trying to get the absolute maximum amount of
brightness from a given LED within its ratings, DC is always best.
This point has been debated thoroughly in sci.electronics.design and
elsewhere, and you can find more info he

http://www2.whidbey.net/opto/LEDFAQ/...Q%20Pages.html

Lighting for electronic cameras (as in the Stocker and Yale link) is
an entirely different matter. Flashing LEDs in sync with camera
frames is an obvious way to reduce power dissipation in the LEDs, but
there is no human visual parallel.

Paul Mathews


Old Nick wrote in message . ..
On Sat, 27 Nov 2004 08:03:59 +0100, "Meindert Sprang"
vaguely proposed a theory
......and in reply I say!:

remove ns from my header address to reply via email

"dazed and confuzed" wrote in message
...
I believe he wants to strobe them faster than the eye can percieve.
something like 50 hz would do it.

Ah, now I understand. But this has no benefits. A LED that is continuously
on at, say 20mA, will appear to have the same brightness as when strobed
with a 20% duty-cycle (1/5 of the time) at 100mA (5 times the current).

Meindert



Actually not quite. If you talk energy consumption then you are right.
But you can viciously overdrivve LEDs to get far more brightness out
of then than they normally can give.

see:
http://www.stockeryale.com/i/leds/lit/app001.htm

There is also argument that your eye and brain think that the led is
still alight and this can fool you into seeing a brighter LED. I would
reckon this would work best for LEDs being looked _at_, rather than
thiose used as a source of illumination.

On Tue, 30 Nov 2004 08:21:34 -0800, Paul Mathews wrote:

[Much very useful information on LED's, electrical efficiency, and
perceived brightness]

Thank you. I found your post very informative!

--Mac

Ah, now I understand. But this has no benefits. A LED that is continuously
on at, say 20mA, will appear to have the same brightness as when strobed
with a 20% duty-cycle (1/5 of the time) at 100mA (5 times the current).

Meindert
[/i][/color]


Actually not quite. If you talk energy consumption then you are right.
But you can viciously overdrivve LEDs to get far more brightness out
of then than they normally can give.

There is also argument that your eye and brain think that the led is
still alight and this can fool you into seeing a brighter LED. I would
reckon this would work best for LEDs being looked _at_, rather than
thiose used as a source of illumination.[/i][/color][/quote]



I have been designing such pulse driven led lights commercialy for over seven years. I have designed and made (still make) all the various LED navigation lights, including anchor lights, and cabin lights too, but some of the cabin models are not pulsed...pulse drive works better for *visibility*.

Yes, pulsing can increase PERCIEVED brightness, if the correct paremeters are followed, it is a well documented human perception phenomena. You don't really need to "overdrive" the leds either, just stay within their temp/current ratings for a given duty cycle. The led driver I use now takes into account input voltage, temperature, and type of led used, and without ever pushing more current through the led than it was designed to handle it produces a pulse train of a frequency, output voltage, and duty cycle such that from a very low voltage to a very high voltage (input) the led will be at a relatively uniform percieved brightness for a power consumption of about 60% of that required to get similar percieved brightness from continusly driven leds. Pulse driving with a carefully controled variable pulse is by far the most efficient way to get maximum percieved brightness, as not only do you utilize the inherently efficient design of switching control (either on or off, no wasting of electricity by turning it into heat) but you can take advantage of the perception factor and get a further boost in performance that makes this design concept superior.
The led nav light drivers I design also incorperate such features as transient, spike,and overvoltage protection, (I have tested the 12VDC light on 115VAC, it shrugged it off) day sensing, bi-polar operation, ect. into retrofit-able led 'bulbs', with the result that when used in a standard fixture they give the same or often even better visibility than the normal incandesecent bulb that they are designed to replace, IE greater than 2NM visibility, but with better functonality, features, and reliability. In fact, they are about as bright as other newer model led anchor lights that use a DC-DC converter to drive their leds, but the pulsed model uses only a small portion of the power that the DC-DC model does. I have reasonably good pictures taken at night with a digital camera that show pretty close to what the eye sees, comparing anchor light fixtures containing both incandesecent bulbs and continuously on leds with the pulsed model that bear this out.
A normal boat could anchor, turn the anchor light on, go away for the summer, and come back and start the engine in the late fall with no worries.

If anybody would like more information about led boat lighting design, I would be happy to send some to them off-list...it is kinda long. I can get carried away. ;-) -Ken

On Wed, 8 Dec 2004 04:17:17 +0000, greenrayled
vaguely proposed a theory
.......and in reply I say!:

remove ns from my header address to reply via email

I for one would happily put in vote #1 for you to simply post to the
roup and save yourself the trouble of multi-sends. It may be long, but
sounds interesting, and On Topic. There has been a lot of "discussion"
about this. If you have reasonable input, even if it promotes dissent
and discussion, that's good IMO.

Others? Opinions?

I have been designing such pulse driven led lights commercialy for over
seven years. I have designed and made (still make) all the various LED
navigation lights, including anchor lights, and cabin lights too, but
some of the cabin models are not pulsed...pulse drive works better for
*visibility*.

Yes, pulsing can increase PERCIEVED brightness, if the correct paremeters
are followed, it is a well documented human perception phenomena. You

snip of some guy going on and on...... GG

If anybody would like more information about led boat lighting design, I
would be happy to send some to them off-list...it is kinda long. I can
get carried away. ;-) -Ken