You could have said that in the first place and saved us all a lot of time. Anybody with a year of experience would know the answer without doing google searches.

Who is "us"?
Once you get into the engineering world, you'll learn that you don't over constrain. First step is to understand the limits, then work within them base on other factors, such as cost, effort, commercial viability etc.
Thanks again all for the good info.

 

"Us" is a few dozen people who contribute their time to help other people on this site.
A few dozen didn't answer you, but you can be sure a few dozen examined your request, then decided whether they could be of service.
As for, "getting into the engineering world", I did that about 50 years ago.

 

A white LED can easily do 100kHz (100,000 Hz). The phosphor and phosphorescent are two different things. The phosphor is a mixture of photo-active chemicals that generate colored light when invisible UV light is applied. Phosphors are not phosphorescent. Phosphorescence is a photo-chemical decay process that goes through the right side of the figure below - a quantum mechanical forbidden transitions. It takes a long time for the electron spin to flip and become allowed or non-radiative decay to occur and allow an excited electron to decay back go ground state (milli-seconds to 100s of seconds).

Phosphors on your television screen or your UV light or the white phosphor on a fluorescent bulb are actually, (as the bulb's name indicates), fluorescent decays. Fluorescent decay is quantum mechanically allowed and occurs in 10s of pico-seconds to 10s of nano-seconds.

A white LED can turn off just a few nano-seconds slower than a bare UV LED. 100kHz has been done on my workbench.

 

A white LED can easily do 100kHz (100,000 Hz). The phosphor and phosphorescent are two different things. The phosphor is a mixture of photo-active chemicals that generate colored light when invisible UV light is applied. Phosphors are not phosphorescent. Phosphorescence is a photo-chemical decay process that goes through the right side of the figure below - a quantum mechanical forbidden transitions. It takes a long time for the electron spin to flip and become allowed or non-radiative decay to occur and allow an excited electron to decay back go ground state (milli-seconds to 100s of seconds).

Phosphors on your television screen or your UV light or the white phosphor on a fluorescent bulb are actually, (as the bulb's name indicates), fluorescent decays. Fluorescent decay is quantum mechanically allowed and occurs in 10s of pico-seconds to 10s of nano-seconds.

A white LED can turn off just a few nano-seconds slower than a bare UV LED. 100kHz has been done on my workbench.

Excellent information. Thanks for the details. As a physicist, you are speaking my language by explaining the mechanism and the key differences between the different behaviors. I am working on an invention, but LEDs are out of my area of expertise, as others have noted! Thanks for helping point me in the right direction.

 

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.

At that frequency, I don't think you have any need for concern.

We had a thread here late last year on this topic and I performed some experiments to determine the response time of various LEDs, including several types of white LED (small indicator-types as well as 3 watt illumination LEDs), along with red and green devices. Results were posted here and here. None of the tested devices had turn-on or turn-off times longer than a few hundred nanoseconds.

 

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.

Will you please share me the formula to get frequency (KHz) from seconds (uS) or reverse? I used an online calculator but getting confuse.

 

Will you please share me the formula to get frequency (KHz) from seconds (uS) or reverse? I used an online calculator but getting confuse.

They are just reciprocals of each other. Frequency is cycles per second and period is seconds per cycle!

Example: A signal at 10 Hz means 10 cycles per second. The period is 1/10 = 0.1 seconds per cycle.

Easy!

Note that in the metric system Kilo (K) and Milli are inverses of each other. 1 Kilo is 1000 while I milli is 0.001

Therefore, 1 KHz has a period of 1 millisecond or ms.

Likewise, Mega and micro are inverses of each other. 1 MHz has a period of 1 microsecond or usec

 

Regular white LEDs can blink at MHz range no problem, as I tried this before.

I know of experiments where people use LEDs as a wifi medium (lifi?). So I think maybe GHz is possible too?

 

Regular white LEDs can blink at MHz range no problem, as I tried this before.

I know of experiments where people use LEDs as a wifi medium (lifi?). So I think maybe GHz is possible too?

Years ago I built a 10.7MHz oscillator around an FM radio IFT, a ceramic resonator and a single transistor.

At first it didn't seem to do much, so I put an inverse parallel pair of red LEDs across the IFT secondary - when I powered it up, it completely jammed the FM radio I'd been listening to.

Both LEDs were producing a faint glow that I could just see by cupping my hand round them to shield out the room light.