Dark Red LED light?

Has anyone found a small dark red LED flashlight? One where on a low setting you couldn't see the light but could on a high setting?

I know they aren't going to sell one with a setting that you can't see so maybe it would have a high setting only but be dark red enough so that if current was reduced much more it wouldn't be visible.

The idea would be to see if there actually is a color where on high the cones are sensitive but not the rods.

Every "red" LED light that I have has visible light no matter how low the setting. I have a Proton Pro that gets so low on red that in a completely dark room on low I can't see the beam of the light past 4 feet.

Obviously only the rods are functioning at this point and I can't see color but they are still sensitive to the LED. Is there actually a dark red LED used in an existing light where the rods wouldn't be affected?

I know in theory you would pick in the high 600 nm range and the rods shouldn't be sensitive but there isn't going to be a ready made light using that with a low mode (if you can't see it) but there might be one with high mode only. You could try to use neutral density filters to reduce the output to simulate a low mode and determine if it isn't visible when only the rods are in play.

Any ideas? I don't have soldering skills or I would just order the bare emitter.

gcbryan said:

Has anyone found a small dark red LED flashlight? One where on a low setting you couldn't see the light but could on a high setting?

I know they aren't going to sell one with a setting that you can't see so maybe it would have a high setting only but be dark red enough so that if current was reduced much more it wouldn't be visible.

The idea would be to see if there actually is a color where on high the cones are sensitive but not the rods.

Every "red" LED light that I have has visible light no matter how low the setting. I have a Proton Pro that gets so low on red that in a completely dark room on low I can't see the beam of the light past 4 feet.

Obviously only the rods are functioning at this point and I can't see color but they are still sensitive to the LED. Is there actually a dark red LED used in an existing light where the rods wouldn't be affected?

I know in theory you would pick in the high 600 nm range and the rods shouldn't be sensitive but there isn't going to be a ready made light using that with a low mode (if you can't see it) but there might be one with high mode only. You could try to use neutral density filters to reduce the output to simulate a low mode and determine if it isn't visible when only the rods are in play.

Any ideas? I don't have soldering skills or I would just order the bare emitter.

Click to expand...

I'm not sure what you're asking. How can a light be 'red' and be 'invisible' at the same time?

red02 said:

I'm not sure what you're asking. How can a light be 'red' and be 'invisible' at the same time?

Click to expand...

Supposedly like our rods aren't sensitive to red however our cones are. The rods are the only thing involved in very low light situations. As the light level increases then the cones become activated.

At a high enough level to activate the cones a dark red LED would be visible to the cones. If you go into a dark room or your backyard at night then your ability to see is only due to the sensitivity of the rods. If rods aren't sensitive to dark red (which is supposed to be the case) then you wouldn't be able to see that same light (at a lower output level that wouldn't activate the cones).

It's a hard thing to test and that's what I'd like to do.

If I am reading your post right, Peak Kilimanjaro with red LEDs and QTC can go very low.

http://www.youtube.com/watch?v=evuXn3pgu7o

Rigel Systems has two lines of flashlights that turn down all the way to dark. They may be ordered with deep red (640-660nm) LEDs for cone games.

If anyone happens to know I'd be curious to know what wavelength the red LED is in the Proton Pro (which I already have). It goes down low enough but it isn't red enough apparently. I'd be interested to know what it is however.

[EDIT] I just read somewhere that the red LED in the Proton Pro is 620-630 nm.

I've had good experience with the Ratshack red LEDs. 1 is kept in a P60 as a battery vampire and the other is in my photon freedom. I had the chance to test both with a spectroscope and both were around 660nm peak wavelength, the packaging said as much. I think ratshack also sells some 700nm LEDs, but its almost impossible to see on low with the photon freedom so I decided to pass.

The ph freedom is pretty much the lowest you can go with a no-hassle mod...

Have you played with the super dark red filters from the Lee Filter book....They look impressive and I may try them out myself. Keep in mind that the wavelength is more important than dimness. With deep red light you can go up to 1 lumen and still preserve scotopic vision.

I've used 660nm deep red LED's pretty extensively in a project. Even dimmed to the point where you can stick your eye up to the emitter and look into it, the light still appears red even after being fully night adapted.

I've read the same arguments as you that "if you can see the color it's too bright" but I work with some pretty darn dim LED's (I'd guess 0.05lm) and I've always been able to see the color, even a half hour later with deep red LED's.

sounds like you are not in true scotopic vision. Scotopic vision can be very difficult to achieve. Even small amount of ambient light (even just looking at paper under moonlight) at night can prevent real scotopic vision. Instead, the eye operates in mesopic vision or a mixed state.

also keep in mind that in scotopic mode, the cones do not disappear. The rods will take over, but the cones will still respond to a intense light(relatively speaking) to see color

Regarding Photo Freedom I have one as well as Proton Pro. I also have the Lee Filters and tried a dark red but I could still see the beam. Ultimately you can just filter the light out of course but that's not the point.

Regarding the comment about seeing red even when dim that's because you have the led right in your eye. At that distance it is (relatively) bright and triggers the cones response.

However if you point the light away from your eyes (as you would use it) you can't see red once it's fairly dim. It doesn't even have to be as dim as some people suggest (I don't think). If you are in a room that you are familiar with you already know what the color is of everything so when you see the various shades of grey you may think you see the color because you already know the color.

You know your lampshade is blue so when you walk though the room at night and see a medium grey over the (turned off) lamp you may think you can detect that it is blue. If you try the same thing in a room that you aren't familiar with however you will realize that you aren't seeing color.

It sometimes seems like you are seeing color when the light level is dim as well because you may see a light in the distance and of course you will see color around that. Take a way around the local park or lake at night and even while it's light enough to see without a flashlight more than likely you aren't seeing any colors (unless there are street lights around of course).

If the Freedom is 660 nm then I guess that's about as good as I'm going to find. I think it's hard to prove then that rods aren't sensitive to red since I can see light coming out of the Freedom even on low.

Rods register black and white, that's it. Color vision is handled by cones. If you are seeing color, the cones are taking over.

Rods are very sensitive to even dim light due to neuronal convergence. In the retina, many rods converge on each bipolar cell and many bipolar cells on each ganglion cell, and a ganglion cell on an optic nerve fiber. Thus, a tiny amount of light on many rods still adds up to stimulate visual signals to the brain. You see in very dim light, however it's in black and white and the resolution is bad. Even still, scotopic vision is functional at a light intensity less than starlight reflected from a sheet of white paper.

Cones handle color vision, and offer very good visual acuity thanks to very little neuronal convergence. Most cones have their own bipolar cells, ganglion cells, and optic nerve fibers. The downside is that they are less sensitive to light as you don't get the cumulative effects like you do with rods. Even still, the threshold for photopic vision is between the intensity of starlight and moonlight reflected from white paper. So my guess is that most lights even very dim ones, will excite cones at least to a degree and allow us to see in color.

The other interesting thing is that red cones peak at 558 nm, which is not the red part of the spectrum, it's orange-yellow. By they are the only cones that respond to red at all. If you wanted to get an "invisible" light, the best you could probably do would be at like 700 nm where rods are not functioning, nor are blue or green cones, and red cones are at their lowest level of response.

dd61999 said:

sounds like you are not in true scotopic vision. Scotopic vision can be very difficult to achieve. Even small amount of ambient light (even just looking at paper under moonlight) at night can prevent real scotopic vision. Instead, the eye operates in mesopic vision or a mixed state.

also keep in mind that in scotopic mode, the cones do not disappear. The rods will take over, but the cones will still respond to a intense light(relatively speaking) to see color

Click to expand...

Yup.

nbp said:

Rods register black and white, that's it. Color vision is handled by cones. If you are seeing color, the cones are taking over.

Rods are very sensitive to even dim light due to neuronal convergence. In the retina, many rods converge on each bipolar cell and many bipolar cells on each ganglion cell, and a ganglion cell on an optic nerve fiber. Thus, a tiny amount of light on many rods still adds up to stimulate visual signals to the brain. You see in very dim light, however it's in black and white and the resolution is bad. Even still, scotopic vision is functional at a light intensity less than starlight reflected from a sheet of white paper.

Cones handle color vision, and offer very good visual acuity thanks to very little neuronal convergence. Most cones have their own bipolar cells, ganglion cells, and optic nerve fibers. The downside is that they are less sensitive to light as you don't get the cumulative effects like you do with rods. Even still, the threshold for photopic vision is between the intensity of starlight and moonlight reflected from white paper. So my guess is that most lights even very dim ones, will excite cones at least to a degree and allow us to see in color.

The other interesting thing is that red cones peak at 558 nm, which is not the red part of the spectrum, it's orange-yellow. By they are the only cones that respond to red at all. If you wanted to get an "invisible" light, the best you could probably do would be at like 700 nm where rods are not functioning, nor are blue or green cones, and red cones are at their lowest level of response.

Click to expand...

Mostly Yup.

Only cones in the macula have a 1 to 1 convergence ratio. As you move out into the periphery of the retina, the convergence ratio increases rapidly, as does the rod density, and the cone density drops off accordingly as well. It's that 1 to 1 ration in the macula and fovea that give us the high acuity vision we have there. But since we conveniently evolved a mechanism to move our eyes, our biology was able to make due with high acuity vision only in the macula, and moving the eyes where ever that acuity needs to be used.

Interesting factoid: human photoreceptors are so sensitive, that under an ideal set of conditions (not that that ever happens of course), someone with normal vision is capable of detecting a candle flame at a one mile distance.

The streamlight nite com..

http://www.streamlight.com/product/product.aspx?pid=164

Has three modes of operation, but the one you're interested is the indicator LED. You would have to sit in a dark room for about 10 minutes before you can see the light. But once your eyes are adjusted, it's quite effective.