940nm LEDs

Flashlights, IR illuminators. Projects, reviews and queries. DIY 'stickies' here too.
superslack
Posts: 75
Joined: 08 Feb 2016, 23:58
Location: Virginia

Re: 940nm LEDs

Postby superslack » 16 Jan 2018, 00:06

My goal is not so much apples to apples as what gets me the best illumination with the least amount of LED visible signature. For example, if 4715AS at 0.7A had better illumination with my camera setup and less emitter glow than LumiLED at 1A, I would choose the 4715AS.

4725s has optical power output of 990mW at 1A with a radiant intensity of 425mW/sr.

LumiLED 940nm 60 degree has an optical power output of 1450mW at 1A. The 60 degree beam angle is similar to dedoming a regular LED in the fact that the light waves are projected more forward. The radiant intensity of the LumiLED is 1190 mW/sr. I am sure you are aware that "throw" distance with an aspheric lens is more affected by brightness of the source being focused than the total light output. The LumiLED is better than 4725S on both counts.

The 4715AS has an optical power output of 1340mW at 1A and 2000mW at 1.5A. Osram only published the radiant intensity at 1A, 780 mw/sr.

However, cameras are not as sensitive to 940nm as 850nm and each camera is a little different there. The question is: What is the best illumination with the least amount of LED visible signature?

lightmesser
Posts: 511
Joined: 09 Jan 2014, 01:19
Location: Eastern Europe

Re: 940nm LEDs

Postby lightmesser » 16 Jan 2018, 08:39

Hmm... 4725S mine overdriven version red dot signature is seen from larger distances. Faint red glow as people here says but still glow :)

There is no such emitter... It is faint red glow low "radiation" vs red glow high "radiation".

So going to 810NM does not seem like a bad idea. Everything will glow anyway :)

phoenix
BRUCE ALMIGHTY
Posts: 4571
Joined: 09 May 2012, 14:40
Location: Aberdeen

Re: 940nm LEDs

Postby phoenix » 16 Jan 2018, 09:42

Lots of professional security camera systems use 940nm illumination and when you look at the illuminator there is no obvious red glow.
However, these illuminators are designed to illuminate a wide area rather than as a spotlight.
I think it's concentrating the beam into a spotlight that causes the red glow to become visible.
By the very nature of NV hunting we tend to use focussed illuminators to get the maximum range possible from our kit, so the red glow is unavoidable.
For short range work such as ratting, an area illuminator could be used and that would have a virtually undetectable red glow.

Cheers

Bruce
LAND ROVER - THE WORLD'S WORST 4X4 BY FAR

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Clunge
Posts: 189
Joined: 08 Apr 2014, 23:32
Location: Staffs

Re: 940nm LEDs

Postby Clunge » 17 Jan 2018, 10:45

The way to compare two illuminators for their optical signature is to adjust each torch so the view through your NV is the same shootable view, with the same brightness and the same area coverage, at the same typical target distance.

THEN

Turn on both torches, at those settings, pointing at the target.

THEN

Walk down to the target and look back at the torches to see which is the least eye-catching.

Sorted.

I've done this several times with 850 and 940nm illuminators. While the 940s are still visible (when I'm dark adapted), they are considerably less eye-catching.

Typically, the old 940nm pill gives the same shootable view at full power as a new 850nm pill at low power at 50 yards through my DIY NV add-on through an MTC Connect at 50 yards.

But looking back from the target area, the 940 illuminator is much less bright. Which is good.

HOWEVER

The 940 won't stretch much further for checking backstops etc, and is harder to focus as clearly.

superslack
Posts: 75
Joined: 08 Feb 2016, 23:58
Location: Virginia

Re: 940nm LEDs

Postby superslack » 17 Jan 2018, 22:51

Clunge wrote: with the same brightness and the same area coverage


How do you achieve this when torches have modes? For example, 940nm at 100% of 1050ma may not be the same as 33% 1.5A 850nm. Maybe it is equal brightness at 65% of 1.5A 850nm. How would I figure that out?


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