# High amps LED pulse

#### MikeA

Joined Jan 20, 2013
239
I have some LEDs that I'd like to get max brightness out of them for a short pulse. They will serve a safety purpose, to grab attention of human eye.

So now I'm wondering, is there a pulse width that is known to reach full brightness as far as the eye sees? I played around with different pulse widths, and it seems at about 50ms the light is perceived as 'fully on'. Any longer, it doesn't get brighter. Any shorter, and perceived brightness decreases.

And juts how high current a pulse can be? I don't have a full spec sheet, I just know the LED is rated at 1A 12v forward. As a general rule of thumb, what is the ratio between duty cycle and current? If it's 1A continuous, as a general rule of thumb, can it be said that it could be driven at 10A at 100ms pulse?

#### gerty

Joined Aug 30, 2007
1,298
I have some LEDs that I'd like to get max brightness out of them for a short pulse. They will serve a safety purpose, to grab attention of human eye.

So now I'm wondering, is there a pulse width that is known to reach full brightness as far as the eye sees? I played around with different pulse widths, and it seems at about 50ms the light is perceived as 'fully on'. Any longer, it doesn't get brighter. Any shorter, and perceived brightness decreases.

And juts how high current a pulse can be? I don't have a full spec sheet, I just know the LED is rated at 1A 12v forward. As a general rule of thumb, what is the ratio between duty cycle and current? If it's 1A continuous, as a general rule of thumb, can it be said that it could be driven at 10A at 100ms pulse?
All of this info should be in the spec sheet. If you try to flash them at 10 amps, I think the only thing you'll accomplish is shortening the leds life if it works at all.
Do you have the spec sheet? How about a part number/manufacturers name.

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#### mcgyvr

Joined Oct 15, 2009
5,394

#### ian field

Joined Oct 27, 2012
6,539
I have some LEDs that I'd like to get max brightness out of them for a short pulse. They will serve a safety purpose, to grab attention of human eye.

So now I'm wondering, is there a pulse width that is known to reach full brightness as far as the eye sees? I played around with different pulse widths, and it seems at about 50ms the light is perceived as 'fully on'. Any longer, it doesn't get brighter. Any shorter, and perceived brightness decreases.

And juts how high current a pulse can be? I don't have a full spec sheet, I just know the LED is rated at 1A 12v forward. As a general rule of thumb, what is the ratio between duty cycle and current? If it's 1A continuous, as a general rule of thumb, can it be said that it could be driven at 10A at 100ms pulse?
One approach is a blocking oscillator, but you can't use the center tapped primary model as you need to tie the other end of the base winding to a C/R charging circuit (this also means you're not tied to the single-cell 1.5V model).

#### Shagas

Joined May 13, 2013
804
I have some LEDs that I'd like to get max brightness out of them for a short pulse. They will serve a safety purpose, to grab attention of human eye.

So now I'm wondering, is there a pulse width that is known to reach full brightness as far as the eye sees? I played around with different pulse widths, and it seems at about 50ms the light is perceived as 'fully on'. Any longer, it doesn't get brighter. Any shorter, and perceived brightness decreases.

And juts how high current a pulse can be? I don't have a full spec sheet, I just know the LED is rated at 1A 12v forward. As a general rule of thumb, what is the ratio between duty cycle and current? If it's 1A continuous, as a general rule of thumb, can it be said that it could be driven at 10A at 100ms pulse?
1A continuous means 1A max .
The led just won't give you more brightness if you exceed the current . Try it yourself and you will see (on a cheap small diode ofcource).There is only a limited amount of light that can be emitted from a given surface area , which means that feeding more current will just damage it and shorten the lifespan.

If you want more brightness then go for a more powerfull LED. You can get 30Watt industrial ones .
Also if you want it to catch the eye then pick and eye-catching color for example red .

To make it even more eye-catching I'd give the pulse a 'tail' , a soft decay.
What I mean by soft decay is this :

I think that the reason that might work better in some cases is because the brain probably doesn't register short pulses very well (at least peripherally) so if it has a tail then the eye can confirm if the even actually did happen.

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#### MikeA

Joined Jan 20, 2013
239
I'm pretty sure continuous is a different figure from max/peak. As heat is an issue first. Some spec sheets for other LEDs that I have do specify max/peak as 200%+ of continuous.

http://www.cree.com/~/media/Files/Cr...sedCurrent.pdf

What's interesting in this document is the lumens vs. current graph. They claim that their LEDs gain very little brightness above and beyond the continuous current rating. The cheap 10W Chinese LEDs that I have and tried pulsing at 200% and 300% of continuous rating, seem to get considerable brighter. Almost linear brightness increase.

#### ian field

Joined Oct 27, 2012
6,539
1A continuous means 1A max .
The led just won't give you more brightness if you exceed the current . Try it yourself and you will see (on a cheap small diode ofcource).There is only a limited amount of light that can be emitted from a given surface area , which means that feeding more current will just damage it and shorten the lifespan.

Some manufacturers publish application notes for pulse driving LEDs, there's a fairly strict relationship between pulse amplitude and duty cycle.

AFAIK the total energy over time is about the same as for continuous current - most of the perceived increase in brightness is due to persistence of vision.

#### Shagas

Joined May 13, 2013
804
Hmm well thevertheless , you won't get a decent answer without having those datasheets of your current LED. I suggest either buying a new one that has a datasheet attached to it or online or just try the tricks that I suggested .

You can try pulsing it at 200% . It might be fine in the long term or it might not be

#### bountyhunter

Joined Sep 7, 2009
2,512
Peak pulse rating will be higher than continuous, but you need to get the rating from the maker. The human eye is non linear so doubling the current does not double perceived brightness. The LED flashlights I "souped up" to get brighter looked about twice as bright when I increased the current about 6X.

YMMV