Luxeons glow after turning off power

Have any of you noticed that luxeons glow after turning off power to them?

I noticed tonight, that my MadMax+ R2H glows for 15-20 seconds after I shut it off.
You must be in near total darkness to notice it, however.

It is somewhat reminiscent of my fluorescent light bulb replacements that also glow after turning them off.

Yes it's the phosphor, similar to a TV screen phosphor. It will only happen with white leds.

Didn't know that. So much for using white led's for tactical purposes to avoid the incan powerdown glow-that-gives-away-your-position. How visible is it at distance?

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Phaserburn said:
Didn't know that. So much for using white led's for tactical purposes to avoid the incan powerdown glow-that-gives-away-your-position. How visible is it at distance?

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Just get a non-white luxeon. (Like a red, amber, green, cyan, blue). These have no phosphor, therfore no afterglow....

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Phaserburn said:
Didn't know that. So much for using white led's for tactical purposes to avoid the incan powerdown glow-that-gives-away-your-position. How visible is it at distance?

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The persistance is *extremely* faint. I am wondering if most of the effect noted in the original post of this thread is actually from the residual charge on the output capacitor of the Madmax.

Hmm. That is possible.

It isn't very noticeable at all. I was in complete darkness, and after shutting the light off, I noticed it in the face of the collimator. I could see it with the head off as well, though.

I should have made the connection to a TV screen, but I didn't think of that.

There is a slight phosphorescent afterglow in all white LEDs, including white Luxeons. That's why oscilloscope traces of them in PWM mode don't really show the falloff as sharply as a single colored LED might produce. There's no way to get rid of this slight afterglow, but you could hide it by pointing the flashlight at the ground or at your face if you had to.

It very well could be the capacitor in the boost circuit causing the glow, as my illuma-lux has no afterglow that I notice. I'll check for it though tonight. I doubt someone would see it from a distance.

Here's a handy link on the subject:
http://www.edwardwillett.com/Columns/luminescence.htm

Actually it's just the burn mark on your retinas/ubbthreads/images/graemlins/wink.gif

The phosphorescent 'frosting' on the semicon cake probably also helps smooth out the 200kHz(?) that madmaxes et al run at, not that your gonna perceive that anyway. It does mean that using a hi frequency in your DC boost circuit is not so critical. After all, CRT's look ok at ~60 kHz.

~ned

Yes, all white LEDs glow for a couple of seconds after they are powered down.

The Boost circuit could also be responsible to a degree, my Arc AAA shows a much slower drop off in light level than a plain white LED connected to a supply.

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Phaserburn said:
Didn't know that. So much for using white led's for tactical purposes to avoid the incan powerdown glow-that-gives-away-your-position. How visible is it at distance?


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The persistance is *extremely* faint. I am wondering if most of the effect noted in the original post of this thread is actually from the residual charge on the output capacitor of the Madmax.


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Is there any way to calculate the slope?

In a related departure, my turquoise Arc AAA's have a neat dimming down when switched off that I have not seen in my white ones. My guess is the phosphor is masking the dimming or the electronics behave differently with the chemistry of the junction. If you turn it on and angle it so you don't see the led and point it at your eye while turning it off you can see it glow down without blinding yourself. It lasts maybe a quarter of a second. It resembles the dimming that a spot light does in style.

Guess I need a hobby, wait this is one?

The afterglow from my Illuma lux is so dim you have to be perfectly in line with the optics and be as close as 3feet. And it goes out very fast. Very hard to notice. I doubt someone who saw you turn on the light would be able to notice the afterglow when you change positions.

Just a semi-realted note, a fair amount of halogen and krypton incan bulbs will glow for a while after being turned off, but that's the actual glass itself glowing rather than the source.

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Zelandeth said:
Just a semi-realted note, a fair amount of halogen and krypton incan bulbs will glow for a while after being turned off, but that's the actual glass itself glowing rather than the source.

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Is that because the glass actually gets red hot?

Brightnorm

If you were using a luxeon in a tactical situation, you would probably shine the light at the person either to see them, or blind them. Either way, I don't think a person's vision would be good enough at any distance to see the slight after-glow of the LS.

About the Halogen bulbs:
I've noticed this a lot, especially with the spotlights.
After they are shut off, there's a deep blue glow from the
glass for about 10 seconds. It's pretty bright in the dark.
But it does not happen with any surefire bulbs, including the M6, even if on for 30 minutes. It's pretty eerie.
Maybe it has to do with the composition of the quartz envelope.