How fast can White LEDs blink?

Thread Starter

SunSeaSkyy

Joined Feb 25, 2016
7
Does anyone know how fast a generic White LED can be made to blink? I know that bare LEDs can blink up to a MHz or more. But the white phosphor coating on White LEDs slows the effective blink rate because of the rate of decay of the phosphor glow.
Is it tens of Hz? Hundreds of Hz? KHz?
 

#12

Joined Nov 30, 2010
18,210
Here's one that is rated for a forward pulse of 50 useconds. That's 50 KHz for a 50% duty cycle if my calculator is working right.
I'm sure there are faster LEDs. This is just what I picked up in a 5 minute search.
Fiberoptic communication suggests hundreds of megahertz, but I don't know if that's anywhere from infrared to ultraviolet.
 

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Thread Starter

SunSeaSkyy

Joined Feb 25, 2016
7
Here's one that is rated for a forward pulse of 50 useconds. That's 50 KHz for a 50% duty cycle if my calculator is working right.
I'm sure there are faster LEDs. This is just what I picked up in a 5 minute search.
Fiberoptic communication suggests hundreds of megahertz, but I don't know if that's anywhere from infrared to ultraviolet.
Thanks much for taking the time to respond. As someone else mentions below, the vertical scale does not make sense to me and has no units.
Regardless, it shows me that phosphor coated LEDs are not that much slower than bare ones. A KHz seems to be no problem.
 

WBahn

Joined Mar 31, 2012
26,064
Fiberoptic communication suggests hundreds of megahertz, but I don't know if that's anywhere from infrared to ultraviolet.
I think that's a different animal entirely -- they aren't using phosphored light sources for fiber optic communication.
 

MrAl

Joined Jun 17, 2014
7,757
Hi,

Fios uses lasers not LEDs.

Note that some LED specs specifically state that they should not be pulsed. Mainly the higher power type LEDs like the Cree. Maybe a lower peak currents it would be ok, but never tried that.

Some white LEDs are pulsed with very fast pulses, but the main thing is to get the rise and fall times fast so as to not burn out the LED (using high current).
 

cmartinez

Joined Jan 17, 2007
7,062
Yep. Today my calculator gets a completely different answer...like 10 KHz.
I suspected something was wrong yesterday!:(
10 kHz is what I calculated yesterday... but then I saw your first calculation and then I thought that something was wrong with me! :confused:
 

ian field

Joined Oct 27, 2012
6,539
Does anyone know how fast a generic White LED can be made to blink? I know that bare LEDs can blink up to a MHz or more. But the white phosphor coating on White LEDs slows the effective blink rate because of the rate of decay of the phosphor glow.
Is it tens of Hz? Hundreds of Hz? KHz?
If it has to be white - an RGB led is as fast as the slowest bare LED in it.

Someone on this forum has said they got a clean square wave on a photo sensor at 1kHz.

Green is a good compromise if you find phosphor persistence too slow.

The original white LEDs are/were blue with a yellow phosphor - probably not all that fast, I think they might be phasing in UV LEDs with white phosphor, which are probably faster.
 

Thread Starter

SunSeaSkyy

Joined Feb 25, 2016
7
If it has to be white - an RGB led is as fast as the slowest bare LED in it.

Someone on this forum has said they got a clean square wave on a photo sensor at 1kHz.

Green is a good compromise if you find phosphor persistence too slow.

The original white LEDs are/were blue with a yellow phosphor - probably not all that fast, I think they might be phasing in UV LEDs with white phosphor, which are probably faster.
Thanks for the info. I am not seeking the fastest. Just what to know what I can expect from a generic white LED. My target freq. is 120 Hz so I'm trying to determine if I'll be ok with any old white LED, or if I will need to pay close attention to get one with right phosphor.
 

Thread Starter

SunSeaSkyy

Joined Feb 25, 2016
7
Thanks everyone for the excellent info. I'm learning a lot.
I am not seeking the fastest white LED. Just what to know what I can expect from a generic white LED. My target freq. is 120 Hz so I'm trying to determine if I'll be ok with just about any white LED, or if I will need to pay close attention to get one with right phosphor.
 

AnalogKid

Joined Aug 1, 2013
8,536
Some white LEDs are pulsed with very fast pulses, but the main thing is to get the rise and fall times fast so as to not burn out the LED (using high current).
Really? Unless there's something very weird about the device physics, an LED is not a transistor and doesn't saturate, so there is no extra power dissipation during the transition region from off to on that is greater than the power dissipation at full on.

ak
 

ian field

Joined Oct 27, 2012
6,539
Thanks for the info. I am not seeking the fastest. Just what to know what I can expect from a generic white LED. My target freq. is 120 Hz so I'm trying to determine if I'll be ok with any old white LED, or if I will need to pay close attention to get one with right phosphor.
Apparently automotive LEDs are PWM driven, and strobe if you catch them at a glance.

Probably most of those are red or amber - but a few are white.

120Hx is probably OK with the blue/yellow phosphor variety.
 
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