# Which part of spectrum activates glow in the dark?



## alanagnostic (Mar 25, 2009)

I have a glow in the dark holder for my Zebralight headlamp and I was playing with it the other day. When I shined a red LED on it it didn't glow much at all. I haven't tried the green or blue LEDs that I have yet. I shined a white LED and an incandescent on it and it light up like a christmas light. Does anyone know which part of the light spectrum will acitivate typical GITD stuff?


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## 65535 (Mar 25, 2009)

As odd as it seems when I had an high power RGB module green seemed to activate the GITD in my wrist band more effectively than either blue or red. Keep in mind you're white light sources probably also pump out quite a bit more power than a red LED. Unless of course you have a high power red LED.


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## alanagnostic (Mar 25, 2009)

Actually the red led that I have puts out a lot of light. I haven't measured it but the red LED is in an HDS EDC that was modified my Milkyspit. It really hurts my eyes if I look at it directly.


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## NeSSuS-GTE (Mar 25, 2009)

The *basic* idea is that the GITD effect is caused by the phosphorescent material capturing a high energy photon that knocks an electron into a higher orbit. That unstable electron orbit eventually drops back down and re-emits a photon.

The wavelength of a RED led is *too long* and its *energy is too low* to have enough 'ummphh' to knock the electrons into that higher shell.. hence it will have almost no effect on charging the GITD material.

You need high energy, short wavelength light to really blast into the electrons and cause a big glow effect... thats why even a tiny amount of UV light *massively* charges GITD objects. UV is a short and high energy wavelength.

White light contains many wavelengths of light including blue and often times UV (depending on the source)... that's why it is also good at charging GITD. And just like 65535 said, white light sources typically pump out a lot more total photons which means more of the ones GITD likes.


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## greenLED (Mar 25, 2009)

NeSSuS-GTE said:


> UV is a short and high energy wavelength.
> 
> White light contains many wavelengths of light including blue and often times UV (depending on the source)... that's why it is also good at charging GITD.


In order of effectiveness to charge GID:

Sunlight (or a pure UV source)
Incans
White Fluorescent/LED


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## Oznog (Mar 25, 2009)

Well, first we MUST know the type of GID, especially the color.

The way photons work is an incoming photon has no charging effect if it's below the minimum energy (above the maximum wavelength). Also any energy in excess of its threshold is wasted.

For most colors, it needs UVA and the 405nm LEDs are by far the most efficient and cost-effective chargers. The more expensive deeper blacklight LEDs are only nice in that they're mostly invisible instead of a brilliant purple cast of a 405. But they're typically not going to produce as many active photons as the 405, and cost 10x more. As per rule #2 above, the extra energy of the shorter wavelength mega-expensive "deep UV" LEDs has no added charging effect.

Red glow powder (red being the lowest energy color) can be charged by green wavelengths. That's the exception. In fact- this is cool- if you charge up green glow powder, put it next to discharged red, it will charge the red! Also a green laser pointer charges red which is pretty awesome.

Blue LEDs can charge green, but it's not very effective. I believe this is due to the bell-curve nature of the distribution, where only a minority of the photons are above the threshold energy. 

Or maybe the individual glow particles have a bell curve on the exact threshold needed to excite them and only a minority of the glow particles will respond to blue. Actually that makes more sense because most blue LEDs have a fairly tight emitted color. As such- and now that I think about it, this has to be it because glow powder does NOT have a tight emitted color wavelength- a brighter blue LED WILL NOT result in greater charging. Because its wavelength will still only be able to excite only a portion of the glow particles, and a dimmer blue LED might have already fully charged the blue-reactive particles anyways.


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## alanagnostic (Mar 25, 2009)

Thanks for all the responses guys. It never hurts to get a phisics and GITD lesson. I didn't even know there were other GITD colors other than the greenish/yellow I normally see. Learn something new every day.


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## Burgess (Mar 26, 2009)

lovecpf
_


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## Oznog (Mar 26, 2009)

Ah it's all complicated. But:
The GITD we grew up with was green zinc sulfide type.
Several years back the Strontium Aluminate type hit the market. It is many times more powerful and lasts many times longer.

SA's most powerful/longest lasting color is green, then aqua, then blue and violet. Green will glow all night and you can easily read by it. Violet is a small fraction of the glow and fades over 10 or 20 min. There are different grades of brightness available here. 

There is a red zinc sulfide. It's not even sold by most vendors and is pretty expensive. It's striking, yet unfortunately very short-lived glow. It is very susceptible to moisture damage.


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## lonesouth (Mar 30, 2009)

I have nothing to contribute other than to say this is one of the most intersting and informative threads I've read in a while. Kudos!


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## avalon11 (Nov 15, 2017)

365nm produce cleanest fluorescence since it contains little violet light but still LED's may emmit white fluorescence. I tested them with blacklight tube and was dissapointed to see low fluorescence range, only cellulose and phosphors glow brightly. Club lights use cheap 405nm.


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