How many lumens of red light can I use before ruining my scotopic nightvision.

anyone know how many lumensfrom a red light you can use before ruining your scotopic vision at night

dd61999 said:

anyone know how many lumens you can use before ruining your scotopic vision at night

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The maximum amount of luminance that can support scotopic night vision is 10^-2 cd/m^2.

It's very comlicated to relate luminance to luminous flux, unless the environment is a uniform sphere. But if we assume that the source is located inside a 10m sphere, and the light source emits uniform light of 30-degree divergence, then:

Illuminated area = 1256/12 = 104m^2

104m^2/10^-2 Cd/m^2 = 1.04Cd

1.04/4.67 = 0.22 lumens

Thus, if you're located inside a sphere with a 10m radius, and use a floody 30-degree flashlight, the maximum amount of light you could use, without disrupting your scotopic vision, would be 0.22 lumens.

yikes where am I going to find a .22 lumen red light?

meuge said:

The maximum amount of luminance that can support scotopic night vision is 10^-2 cd/m^2.

It's very comlicated to relate luminance to luminous flux, unless the environment is a uniform sphere. But if we assume that the source is located inside a 10m sphere, and the light source emits uniform light of 30-degree divergence, then:

Illuminated area = 1256/12 = 104m^2

104m^2/10^-2 Cd/m^2 = 1.04Cd

1.04/4.67 = 0.22 lumens

Thus, if you're located inside a sphere with a 10m radius, and use a floody 30-degree flashlight, the maximum amount of light you could use, without disrupting your scotopic vision, would be 0.22 lumens.

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Is this regarding white light or red light, thanks

dd61999 said:

Is this regarding white light or red light, thanks

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That would be white light. At 600nm, the rods are almost 10X less sensitive, thus you could probably put out 10X more lumens and still retain your scotopic vision.

Cool info! I've always been interested in learning about the relationship between LED color and night vision.

Meuge, do you have figures for other LED colors (blue, green, Y/G, etc.)?

greenLED said:

Cool info! I've always been interested in learning about the relationship between LED color and night vision.

Meuge, do you have figures for other LED colors (blue, green, Y/G, etc.)?

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Well, white light implies a broad-spectrum emission between roughly 400nm and 700nm. LED-based white light isn't a simple function, because it's bimodal (in its current iteration), and only incadescent lights cover all wavelengths (albeit not equally either). The white LEDs have 2 phosphors, one that has a narrow short-wavelength peak, and a broader long-wavelength peak. I wouldn't be able to give you exact figures, because I lack the mathematical training to do it.

If you want to see the color sensitivity curves, refer to this Wikipedia article:

http://en.wikipedia.org/wiki/Candela

meuge said:

That would be white light. At 600nm, the rods are almost 10X less sensitive, thus you could probably put out 10X more lumens and still retain your scotopic vision.

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Even if you use a "red" with a wavelength longer than rod sensitivity (640 nm) there is the issue of 'cone burn in'. Orange-reds and true-reds are so hard to see with that many are tempted to use them so brightly that an afterimage may be burnt into the cones that may completely overpower the dim image from the rods. So it's very easy to use a red light and preserve your scotopic vision and render it totally useless at the same time.

So what lights are out there that work to preserve scotopic vision.

Maybe the question should be, how much lux from a red light can I use before I ruin my scotopic vision? One lumen of red light spread out in a wide pattern may be just right, but that same one lumen collimated into a bright spot might ruin our night vision.

Bill

dd61999 said:

So what lights are out there that work to preserve scotopic vision.

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Surprisingly, (to me, at least) Dark Adapted Vision is still a controversial subject even in the 21st century. Searching around will show that this may be pursued by following any number of completely different strategies -- all of them having merit to one degree or another.

• Some will rely on any light as long as the people who sell it to him call it 'red'.
• Some will insist on a red light that won't directly interfere with their rods. (wavelength longer then 640 nm)
• Some will use white light at very, very low levels for this purpose.
• Some will use green light at very, very low levels for this purpose.
• Still others will use blue/green light at very, very low levels for this purpose.

I fall into the last catagory.

All of these strategies work to a greater or lessor extent -- most may be made to work very well. Part pf the variation lies in the fact that red light is so very difficult to use for shape recognition.

Another factor may be whether or not you may be being hunted by someone with Night Vision gear. Red lights have a huge IR signature which looks like a beacon through any modern NV gear.

So really, there are many ways to do it that really work to a greater or lessor degree and there are also many who wil say that there is only one way to do it.

If you use red, you have to avoid dazzlling your red cones -- I find red very problematic.

If you use green or blue/green you must find a light that will dim down much, much farther than most lights -- like the Rigel MIL-Starlight and the Photon Freedom NV green w/covert nose.

Most who use white, blue or blue/green strive to use them at levels that only bleach rhodopsin (visual purple) at very close to the rate it is produced -- so they never go very far in the hole.

With whatever color you use two operating rules are iron clad -- (1) always use as little light as possible and (2) be very, very careful where you point it. With the reds any reflections may dazzle your cones and with the greens and blue/greens any splash will wipe out your rod's output in a heartbeat.

There has been lots written on the subject here and through the web and it's a great topic to read about (with all the different approaches). Then you can do your own experiments and find out what will work best for your circumstances.

It is by no means a one-size-fits-all situation.

dd61999 said:

So what lights are out there that work to preserve scotopic vision.

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Depends on what you're doing. For enough intensity to read with while preserving scoptopic vision, using a true red light is probably your only choice. The only problem is that the eyes have a pretty difficult time focusing long wavelength red light, without using so much that it causes the "afterimage" problem discussed earlier. Some sort of red light that was diffused (no distinct hotspot) and that could be ramped up until just enough was produced to actually discern the text, would probably be one's best bet.

For finding my way in the dark, I use my LF2 keychain light (white) on its lowest setting, and aim it pretty far ahead of me -- output is only about 1/10th of a lumen on the lowest setting, and it's fairly diffused, but with scoptopic vision it's just enough to see with -- similar effect to moon light. Without night-adapted vision, a setting that low is really only good for looking at things a couple feet front of me (which is all I want if I'm looking through drawers, or under seat cushions etc)

Maybe the question should be, how much lux from a red light can I use before I ruin my scotopic vision? One lumen of red light spread out in a wide pattern may be just right, but that same one lumen collimated into a bright spot might ruin our night vision.

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You won't be able to see anything with low intensity red because you have zero scoptopic sensitivity there -- it takes a lot of red light before you can even see with it at all. I find red flashlights actually create a "tunnel vision" effect for this reasons -- with a red photon light in the dark, I can ONLY see things that are directly lit up in the hotspot, and nothing else. If I do a ceiling bounce with even a very bright red LED, it becomes essentially useless. On the other hand, if I ceiling-bounce a much dimmer green or white LED I can generally see the whole room clearly.

Blue/green light is great at a very low level for reading.

Is your question regarding a specific task or just out of curiosity? As 2xTrinity stated, it's very important to know what you need to do with the light to determine which light will work best for the task. That basic concept doesn't come up often enough.

For example, a light to use to find the bathroom or refrigerator at night might not work to read at night, and that light might not be the one to use for map reading or star gazing. Do you want a light that has a narrow beam, or a slightly broader spot, or a light that floods?

Sometimes you want more light, sometimes less. Adjustable levels are almost always a good idea for lights used at night. Are you worried about glare or reflections? Will it be used around other people and would their night vision be a consideration?

"Night vision green" works for some tasks and red for others, and other times you'd like to have the option of switching between colors. Maybe another color would work better for your task. Do you need to read charts, maps, or text? Do you need to move around over differing terrain? Are you going to use the light for blood tracking game?

As you can see without more information we can play "20 Questions" for quite awhile. Tell us what you need a light to do and we'll give you a lot of options.

this light will be used for hiking at night outdoors and observing nightlife

dd61999 said:

this light will be used for hiking at night outdoors and observing nightlife

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I've read that many game animals can not see green and some lights are advertized that way. I've observed that rats can't see red light.