Any IR LED's that emit NO visible light?

smack2000 · Oct 8, 2010

Hi There,

I've done some due dilligence searching this forum for an answer but no luck.

I have been searching high and low for an IR LED that emits NO visible light. Every one I've seen (granted only a few) emit some trace of visible light that is quite obvious in total darkness when you look directly into the light. Is there such a thing as an IR LED made well enough as to not emit any visible light, or am I searching for something that doesn't exist?

I am contemplating the purchase of a SF M1 but have found out it too emits some visible light, but I'm also wondering if putting the SF IR Filter (meant for the incans) on the M1 would work and/or be the best possible solution...

Thanks
Scott

mattheww50 · Oct 8, 2010

Going to depend upon the 'cutoff' on the IR filter and how effective the filter is.

And as a practical matter IR LED's don't actually emit light in what is considered the visible spectrum. What happens is the source is in fact VERY BRIGHT in the near IR spectrum. While your eye sensitivity to near IR is very poor, it usually isn't zero. Hence the ability to see a very bright near IR source at close range.

PhotonWrangler · Oct 8, 2010

smack2000 said:
Hi There,

I've done some due dilligence searching this forum for an answer but no luck.

I have been searching high and low for an IR LED that emits NO visible light. Every one I've seen (granted only a few) emit some trace of visible light that is quite obvious in total darkness when you look directly into the light. Is there such a thing as an IR LED made well enough as to not emit any visible light, or am I searching for something that doesn't exist?

I am contemplating the purchase of a SF M1 but have found out it too emits some visible light, but I'm also wondering if putting the SF IR Filter (meant for the incans) on the M1 would work and/or be the best possible solution...

Thanks
Scott

Anything with a wavelength of 900nm or longer should be invisible. I've stared directly into TV remote controls in total darkness and I've seen absolutely nothing. The longest wavelength that I've personally been able to see, dimly, is ~850nm.

Steve K · Oct 8, 2010

They exist. My only personal experience is with 5mm IR leds sold by Radio Shack a decade ago. Well, there's also experience with IR lasers back when I did defense work... very invisible, and very dangerous if you forget that the laser is turned on (and took off your laser goggles).

I get the feeling that you are looking for high power IR leds, though.

Steve K.

nailbender · Oct 9, 2010

Hi
940 nm is about as good as it will get in surface mount. It is as invisible as you will find and is very hard to see. Even while holding in your hand you have to look very close to see if it is working.

Osram makes couple different emitters that work in the 940nm range. They can be found at the regular vendors such as digikey, arrow

If you decide to go with a filter flashlightlens.com has the best I have found but they may not have the size you are looking for.

smack2000 · Oct 9, 2010

Thanks, everyone, for the responses. I'll try picking up one of the Osram 940 nm led's from digikey and see how well it works.

- scott

jellydonut · Oct 9, 2010

The Osram Ostar 940nm LED has a red 'glow' to it in darkness. I've only inspected it at arm's length though, don't know if it's obvious at all at any kind of distance.

Come to think of it.. that's worth a try isn't it? I'm gonna see to it once it gets properly dark tonight. I'll edit this reply once I have anything to tell/show

PhotonWrangler · Oct 9, 2010

jellydonut said:
The Osram Ostar 940nm LED has a red 'glow' to it in darkness. I've only inspected it at arm's length though, don't know if it's obvious at all at any kind of distance. Come to think of it.. that's worth a try isn't it? I'm gonna see to it once it gets properly

If you're able to see a dim red glow from that LED, I'm guessing that it's output spectra is fairly broad and you're seeing some of the shorter wavelengths from it. I doubt that this woudl present an issue at night, however if it was, you could always drop a longpass filter in front of it to attenuate those wavelengths.

jellydonut · Oct 9, 2010

Just checked, and the red glow is ominously present even at a distance. I am guessing with dark adapted eyes looking straight at it it would be quite obvious.

Photos are pointless since IR isn't entirely filtered out and looks pink/purple to the camera for some reason.

CKOD · Oct 9, 2010

jellydonut said:
Just checked, and the red glow is ominously present even at a distance. I am guessing with dark adapted eyes looking straight at it it would be quite obvious.

Photos are pointless since IR isn't entirely filtered out and looks pink/purple to the camera for some reason.

That just seems to be how imaging sensors seem to respond to UV and IR. Not so noticeable with UV since a lot of UV sources you may point a camera at are emitting a ton of blue and violet also. More noticeable with IR. IVe seen someone smoking a cigarette on camera and the tip of teh cig had a very purple tone to it from the IR.

jellydonut · Oct 9, 2010

It's quite funky

The visible light there is from the UV emitter now looks cyan, while the IR beam that normally isn't visible at all looks the way the UV emitter's visible beam does to the naked eye.:candle:

Flx · Oct 9, 2010

@jellydonut: How about you're one of those people with a wideband vision? Just like teens can hear higher frequency sounds than older people do, some folks see further into the light spectrum, i.e. "deeper" reds.

Also, at high power, the ends of the wavelength bell curve get strong enough to be yield visible reds.

The most elegant solution would be to use a narrow bandwidth emitter. Try bugging Sumitomo Electric Industries (I already did) to bring their new chips to the market:

We have developed the world highest optical output power infrared light emitting diode (LED) at 940nm. With a newly developed epitaxial layer structure and a p-type electrode, the optical output power was increased to 5.3 mw at 20 mA DC current, which was about 2.5 times higher than that of a conventional 940 nm LEDs. Forward voltage was 1.35V. The full width of half maximum (FWHM) of spectrum wavelength of the device was 25 nm, which is less than half of that of the conventional one.

Full PDF: http://global-sei.com/tr/pdf/electronics/70-10.pdf

...as you can see, you'll also get twice the battery life, as an added bonus!

smack2000 · Oct 11, 2010

Flx said:
The full width of half maximum (FWHM) of spectrum wavelength of the device was 25 nm, which is less than half of that of the conventional one.

Does this mean you can expect it to emit at 940nm, +/- 25nm? And that you should normally expect +/- 50 nm?

alpg88 · Oct 11, 2010

those ir leds that emit no visible light are weak, those that emit very faint glow are a lot stronger, you wanna use those, i wouldn't be concerned with the glow, it is really dim, but if you are, ir pass filter should be used, simplest and very effective ir pass filter is a overexposed color photo film, every roll has "black"\overexposed end of the film, whenever you load 35mm film you expose 3-4 or so inches, that is ir pass filter. some development places throw it away, you got to tell them to keep that part, or just buy a film, pull it all out let it sit exposed for few min. than give development place to be developed, you'll have plenty of ir pass filter film.

Flx · Oct 11, 2010

smack2000 said:
Does this mean you can expect it to emit at 940nm, +/- 25nm? And that you should normally expect +/- 50 nm?

Actually it's ±12.5 and ±25, respectively. However, keep in mind that a FWHM merely indicates a point where the light is half as intense as it is at its peak wavelength. Just look into any datasheet and find that bell curve: you'll see that the full bandwidth is almost 200nm (±100nm)! Therefore, if you go with an 850nm emitter like alpg88 suggested, your emission will reach 750nm which is the approximate upper limit of the human eye. Many a security camera uses 850nm emitters which look like decorative plain red LEDs around the lens.

alpg88 said:
those ir leds that emit no visible light are weak, those that emit very faint glow are a lot stronger, you wanna use those, i wouldn't be concerned with the glow, it is really dim, but if you are, ir pass filter should be used, simplest and very effective ir pass filter is a overexposed color photo film, every roll has "black"\overexposed end of the film, whenever you load 35mm film you expose 3-4 or so inches, that is ir pass filter. some development places throw it away, you got to tell them to keep that part, or just buy a film, pull it all out let it sit exposed for few min. than give development place to be developed, you'll have plenty of ir pass filter film.

alpg88 · Oct 11, 2010

yep 850nm that is what i used for my ir array for my Sony with night shot.
200mw 1.5v 100ma

i tried ir pass filter, it worked fine, but glow is so dim i didn't bother with filter, other that just test it.

jspeybro · Oct 17, 2010

not sure what you're trying to do, but if you want to hide the leds, try Pespex black 962 which is transparant to IR but black to the eye. If you hold a bright source (incandescent lamp for example) you can still see a faint red glow, but I doubt you can see it when an infrared led is behind it.
940nm shouldn't be visible to the eye, I can't even see 850nm.

osram has a nice range of IR leds, available via farnell and similar companies.

darknessemitter · Oct 28, 2010

jellydonut said:
It's quite funky

The visible light there is from the UV emitter now looks cyan, while the IR beam that normally isn't visible at all looks the way the UV emitter's visible beam does to the naked eye.:candle:

This tends to happen because the RGB filter arrays used in consumer digital cameras are only designed to filter visible light. If the IR/UV source strong enough to get through the hot mirror, the RGB may be transparent in IR and UV wavelengths.

For example, since the camera relies on knowing which color filter is covering which pixel for color rendition, IR radiation that passes through the blue filters will be interpreted as "blue" light.

lebox97 · Oct 28, 2010

It has been touched on - but not discussed

AFAIK from the military/LEO users I work with...
there is a significant difference in illumination output between the 850 and 940nm wave lengths
something like hundreds of feet vs dozens of feet.

ie. if you are trying to be ultra stealthy - and only need to "see" 15-30 feet ahead of you go with the 940nm
if you need maximum illuminating distance go with the 850nm, but you need to be more discreet with it's use - if you need to be stealthy.
:shrug:

the above also then depends on what NVG gear you are using (Gen III/II/I) - I am told the latest stuff is pretty amazing and ultra sensitive.

Tod

CuriousOne · Oct 14, 2012

I have a bunch of IR leds, removed from checkpoint security scanner, which are totally invisible to human eye, but are very bright. I have no idea what model they are or who did them. I've determined that they need about 50ma per for best light/power consumption ratio. They are plain 5mm blue colored leds, just like ones you can see in remotes. And I suspect, they aren't 940nm, since I've compared them to some OSRAM 940nm leds, which consume much more, but are less visible in my camera.

Any IR LED's that emit NO visible light?

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