# Deep Red LED



## TyJo (Sep 13, 2011)

I want a light with a "deep red" LED, something around 660nm or larger preferably. I only need 1 fixed output from a range of 2-10 lumens, the lower the better. I would like the light to run off of AA or AAA NiMH batteries. I want this light for preserving night adapted vision, I have done a lot of research and I definitely want a "deep red" led. I found this LED, http://www.ledengin.com/files/dist/5wLZ/LZ1-00R205.pdf. A few questions...
Is this LED fine for my usage?
I'm assuming I have to look at customs to get this LED or similar into a light, what is the best way of going about that? I have posted in Peak's thread, is there anyone else?


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## SemiMan (Sep 13, 2011)

TyJo said:


> I want a light with a "deep red" LED, something around 660nm or larger preferably. I only need 1 fixed output from a range of 2-10 lumens, the lower the better. I would like the light to run off of AA or AAA NiMH batteries. I want this light for preserving night adapted vision, I have done a lot of research and I definitely want a "deep red" led. I found this LED, http://www.ledengin.com/files/dist/5wLZ/LZ1-00R205.pdf. A few questions...
> Is this LED fine for my usage?
> I'm assuming I have to look at customs to get this LED or similar into a light, what is the best way of going about that? I have posted in Peak's thread, is there anyone else?


 
You can get Lumileds REBELS in deep reds now. Just buy a flashlight with a real constant current source drive and replace the LED.

Semiman


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## Mike S (Sep 13, 2011)

Could you under-power a lower bin deep red Rebel? They have a typical wavelength of 655 nm, but can go as high as 670 nm.

Edit: Beaten to the punch.


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## SemiMan (Sep 14, 2011)

You don't really need anything exceptionally deep in color. Eye response for the iris is mostly in the blue. Single color LEDS (most) are monochromatic.

Semiman


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## calipsoii (Sep 14, 2011)

I use these on my deep red A2 rings. It's a very deep ruby color - no pink and no orange. They aren't as bright as the standard red LED's, and they have a 50 degree beam angle so they're pretty floody, but I really like the tint and I think they'll do a fine job for what you need them for.

My recommendation is to pick up a cheap Fauxton from DX or your local store (one of those coin-cell squeeze lights) and swap this LED in.


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## MikeAusC (Sep 14, 2011)

I'll be buying this 5mm 700nm 18mcd 30deg Red http://www.purdyelectronics.com/pdf/AND113.pdf This datasheet also shows the spectrum for other Reds e.g. for a 625nm Red, the intensity at 585nm is 10% of the peak, and 585nm is well into the Scotopic response curve.

It costs all of $0.29 http://au.element14.com/optoelectronics/113rp/led-t-1-3-4-red-18mcd-700nm/dp/6405150

They also make a 60 deg version AND114.

700nm places it at the extreme of Photonic sensitivity, but the advantage is that the Scotopic sensitivity curve is miniscule at 700nm. At 625nm the output from this LED is trivial.

18mcd isn't much, but if you want to preserve night vision, you need to keep even deep Red light to a minimum. Depending on which Photopic curve you look at, 700nm sensitivity is less than 0.5% of the peak at 555nm.

If you're going to transplant it into a host originally designed for White, keep in mind that Red LEDs have much lower voltage than White.


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## Kinnza (Sep 14, 2011)

There are some models of deep red out there that can accomplish the task. Lumileds Rebel and Osram Golden Dragon Plus are the main options. But you have too LEDEngin and Edison Opto models.

The Rebel and the GD+ emits about 20lm at 350mA, so they are more than enough for your needs.

The Osram Oslon SSL 80 has same output but emitted on a narrower beam angle, 80º.

In order to keep night adapted vision, you just need to avoid emission below 620nm. Normal red LEDs, with typical peak at 630-635nm already emits little below 620nm,so probably with dim lighting level it won't interfere with night vision. If you are able to find a red LED with dominant wavelenght over 625nm (some manufacturers bin red color by dominant wavelength), it should work fine.

But in order to be sure, you dont need to use 660nm deep red LEDs to keep night adapted vision. There are red LEDs between them, with peak wavelengths around 645nm. I'm not aware of any in high power, but in medium power there are many options. Typical signaling TopLeds have this color, with emissions of 2-3lm (at 50mA). An Osram Advanced TopLed runs at 140mA (up to 200) with a typical emission of 13.4lm, a little more than 9lm on operating conditions, at 2.1V. This option would suit your needs, is cheap and offer a very long runtime.


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## SemiMan (Sep 14, 2011)

MikeAusC said:


> I'll be buying this 5mm 700nm 18mcd 30deg Red http://www.purdyelectronics.com/pdf/AND113.pdf
> 
> It costs all of $0.29 http://au.element14.com/optoelectronics/113rp/led-t-1-3-4-red-18mcd-700nm/dp/6405150
> 
> ...


 
There are several factors at play in night vision, but mainly center on rhodopsin concentration in the rods, and iris opening.

Rhodopsin concentration is pretty much a factor of exposure to light according to the sensitivity of rhodopsin absorption which pretty much matches the scotopic response.

That is really a double edged sword ... use a wavelength where rhodopsin absorption is low, and you don't reduce rhodopsin concentration ..... but you can't see cause you have no sensitivity. Or use a color with good rhodopsin absorption and you lose rhodopsin concentration ..........

Simple summary: your loss of rhodopsin concentration (and hence part of night vision) is a function of how "bright" the light is (based on the scotopic vision), not simply the wavelength. A deep red LED of the same "brightness" as a green LED will reduce your night vision via reduction in rhodopsin conversion by the same amount.

Iris response is controlled mainly from melanopsin sensitive nerve cells (somewhat recent finding). That peaks around 470-480nm and drops to virtually nothing by 600nm. There are other factors on pupil response (still being understood completely), but pretty much the control is all sub 600nm.

When you take those two things into account, you don't need a LED at 700nm to maintain night sensitivity. Pretty much anything past 600nm is not going to stimulate the pupil and rhodopsin absorption is a factor of scotopic brightness so you may as well pick something as bright as needed but no brighter.

Semiman


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## MikeAusC (Sep 14, 2011)

SemiMan said:


> . . . . A deep red LED of the same "brightness" as a green LED will reduce your night vision via reduction in rhodopsin conversion by the same amount . . . .



- except that the relative "brightness" of green/red are quite different for Scotopic versus Photopic vision. That is the whole reason for using red light - when PHOTOPIC vision is needed, whilst minimising desensing of Scotopic vision.




SemiMan said:


> . . . . When you take those two things into account, you don't need a LED at 700nm to maintain night sensitivity. Pretty much anything past 600nm is not going to stimulate the pupil . . . .



If you're interested in preserving night-vision, you'll be at such a low lighting level that the iris will be virtually fully open.


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## Sub_Umbra (Sep 14, 2011)

IIRC *Rigel Systems* offers very deep reds in all of their models as a option.


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## MikeAusC (Sep 15, 2011)

There's already an active thread on selecting lights for maintaining Night Vision http://www.candlepowerforums.com/vb/showthread.php?317091-Lights-that-maintain-dark-adapted-vision


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## TyJo (Sep 15, 2011)

MikeAusC said:


> There's already an active thread on selecting lights for maintaining Night Vision http://www.candlepowerforums.com/vb/showthread.php?317091-Lights-that-maintain-dark-adapted-vision


Thanks I have been posting in that thread, this thread was more focused on the LED itself. I'm gonna put this on hold for now since there doesn't seem to be a custom manufacturer that could do this reasonably and I am probably going to be fine using my low low multimodes for the time being.


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## SemiMan (Sep 16, 2011)

MikeAusC said:


> - except that the relative "brightness" of green/red are quite different for Scotopic versus Photopic vision. That is the whole reason for using red light - when PHOTOPIC vision is needed, whilst minimising desensing of Scotopic vision.
> 
> If you're interested in preserving night-vision, you'll be at such a low lighting level that the iris will be virtually fully open.


 
Mike,

You started off with a great point to be made, then shot yourself in the foot with the second point unfortunately.

You are absolutely correct. Out past 630nm, the "relative" photopic sensitivity is higher (much) than the relative scotopic sensitivity. Unfortunately, but I need to check better (going off memory), the absolute sensitivity is not better.

I.e. You are absolutely correct that a deep red LED will have more ability to trigger cones without triggering rods. However, I believe the level required to trigger said cones will still be high enough that it will also be firing rods and hence killing your night vision at least where you are looking.

I remember it being very difficult to get a highly accurate absolute comparison of photopic and scotopic deep into the red. The graphs all make it look like the scotopic drops to nothing which relatively it does, but absolutely compared to photopic it does not.

Semiman


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