Soul Afterglow?

[JamisonM]

I noticed something that I thought was pretty neat with my 4D Molkoff while walking the dog; it has an afterglow. When you cut on the light and then turn it off, you can watch as the light coming from the emitter quickly goes out. It only lasts a second or two. At first I thought this was pretty neat, but then I started thinking that this may be something I should be concerned about. Is this something I should be worried about or is this something that isn't uncommon? Here's a short clip I took with my camera.

 

[qip]

all 3 of mine do same thing, its just cooling down i guess

 

[PhotonWrangler]

It looks like a brief moment of phosphorescence, nothing to be concerned about. It's likely caused by one of the ingredients of their phosphor blend. The only consequence of this behavior would be a very tiny, negligible reduction of contrast while operating in strobe mode.

 

[JamisonM]

That's good to hear. Do other similar powered LEDs do this as well?

 

[Jarl]

It's all to do with the phosphors used to turn some of the blue light to red and green, giving a better CRI. Depending on the mix, the afterglow of phosphors can be changed- glow in the dark toys have a very long afterglow, whereas something like the phosphors used in a CRT or plasma screen have very short afterglow periods- if they didn't, the response speed of the screen would be truly awful.

Although I haven't seen this behaviour with the rebels and Q5's I've used (possibly because I don't often stare down the barrel as I turn it off!), it's nothing to worry about.

 

[AvidHiker]

I have only 2 Seoul lights, one very clearly does this and the other is a Surefire Titan - I can't notice any afterglow there (leaving on high and unscrewing the battery cap). Maybe because the Titan doesn't drive the LED very aggressively.

I have a Malkoff Quad with Cree Q5s and I couldn't abserve a trace of glow on that either (and the LEDs are certainly not underdriven there) - kind of a dangerous experiment, I exposed my eyes to that beam once for less then a second and saw spots for 30 minutes. I suspect it must be the different phosphor composition used by Seoul. My SF L2 with the good old Lux V doesn't appear to glow either.

 

[lumenal]

I noticed the same after-glow on my Malkoff 4D - and asked Gene about it. He said that its completely normal.

 

[JamisonM]

I noticed the same after-glow on my Malkoff 4D - and asked Gene about it. He said that its completely normal.

I'm glade to hear that.

Thanks guys. Good to know I can take the light out while walking the dog and not have to worry about it dieing on me.

 

[Xak]

My Amilite T5 does that too. Kinda cool.

 

[Planterz]

"White" LEDs aren't white. They're blue LEDs with the die coated in phosphors. The blue light excites these phosphors, which glow, making the LED produce what we see as white light. Like everybody else said, what you're seeing is the afterglow of the phosphors when the LED is turned off.

 

[Ray_of_Light]

The afterglow is the effect of the smoothing capacitors that are present in the LED drivers.
Not all drivers use smoothing capacitors.
The phosphors used in power LEDs doesn't have the necessary persistence to produce a perceptible afterglow.
Regards

Antony

 

[PhotonWrangler]

Good observation, Antony. It's a common phenomenon on ac adaptors that have an LED power indicator. Those capacitors in flashlight drivers are pretty tiny though, so any afterglow from capacitor discharge would probably be really, really brief. It might be a combination of factors.

An easy way to confirm this is to illuminate the LED with another, external blue LED to charge the phosphors, then extinguish the external LED and look for afterglow in the phosphor.

 

[JamisonM]

It seem to be the driver rather then the LED. I took my MT-III and pointed it at the business end of my 4D Malkoff and got nothing.

 

[IsaacHayes]

It's normal for anything that uses a phosphor. CRT monitors and TV's will have an afterglow as well. If you have a strong light or UV light you can "write" on them when they are off at night too.

Also for more glowing fun, the Seoul phosphor mix seems to react brightly with UV, while other LEDs just react with blue light.

Oh and if you have a direct drive flashlight, maybe a P7 DD light someone can try this, but turn in on and take off the tail cap. In total darkness put your finger across the battery in the tail, and touch the body tube where the tail normally would. A tiny amount of current will flow through your skin and make the LED light up ever so dimly. Take the finger on/off to see it working! (won't work with lights that use drivers)

BTW I like your avatar! The dog's eyes are freaking me out! hahah