Can someone explain to me the use of a light that makes <10 lumens?

[asdalton]

I can't believe that this thread has gone on for so long. :sigh:

The fact is that many people find a light with an output < 10 lm to be useful for a variety of things. The fact that some people don't see the need for such a dim light is irrelevant; the dim lights (or multi-level lights with dim levels) aren't being marketed to them.

I personally don't have much use for flood-only lights such as the McGizmo Mule, but I'm not challenging other people to justify why they "need" such a light.

 

[Woods Walker]

I just got back from a winter camp/hike on the AT. Used my H50 and leatherman S2. The 2 ish lumens of the H50 low was more than enough for inside my tipi heated shelter. The 13ish med was enough to cut wood for the stove. Too much light tends to blind me when I turn it off. A little light in the woods goes much more than in the city. A good low is so under rated.

 

[Oddjob]

I'm amazed this thread is still going. Everyone will find and use what works for them. We all have so many similarites as evidenced by the numerous bathroom examples but we are also different and so what works for one person will not work for another. Experience is the best teacher and until something chages we use what we decide is best for us at the time.

 

[deusexaethera]

That's true for me. Once I know I'm positioned correctly, I'm pretty much as good an aim in the dark as in the light. Not that that's saying much... :naughty:

 

[kaichu dento]

After reading all three pages of this thread, it seems to me that the situations people are using 1-2 lumen lights in are either tactical in nature, overly-cautious (in my opinion), or situations in which I would simply use what my mother gave me to see where I'm going. That's probably why I didn't understand before.

I'm somewhat of the same frame of mind as you in that I typically won't use a light at all in situations that many others do, such as walking along dark trails in the woods and such. However there are those times when you simply can't see well enough to walk with confidence and end up trying the 'blind' walk, where you inch along and try to feel the ground to make sure there are no surprises in the trail. One particular trail here had a huge gap until recently caused by a water leak and had steep sides on it, which I found to be much easier to cross with a quick flash.

With my light set low enough I was immediately back walking without even a moment of disrupted night vision.

I use my lights as a tool as much as possible, and not a crutch, and an extreme low setting, something which I couldn't even imagine wanting a year ago, has become a major choice factor in choosing a light for me.

 

[Cheapskate]

"When using a red light at night, you are seeing using only the red cone cells, not the rods. Using the brighter red light will have no impact on your dark adapted rods, but the dimmer white one will, because the light contains higher wavelengths that the rods are sensitive to."


Respectfully, I must disagree. I woke up somewhere between two and four A.M. this morning to visit the bathroom. We are having our main bathroom redone, so I had to venture downstairs to an auxillary toilet. I grabbed my miniM@g retrofitted with a red Niteize dropin, running off a single AA cell plus a dummy cell. I had to cover the light head with my fingers to drop down the output. I know there is a thread hanging out somewhere (I'll look in a minute and find the relevant post) where a member wrote something along the lines of, "Between a *very* dim white light and a *very* dim red light, the red light will affect (negatively) one's night vision to a lesser extent. However, a red light of sufficient brightness *will* cause one to lose one's night vision." I am aware of the argument based on wavelengths, and I really wanted to believe it. However, I can state from direct empirical observation that even those three measly 5mm red LEDs off a single AA alkaline cell (too weak to use in any other light) are too bright for fully dark-adapted vision.

So, yes, there is an excellent use for a light source that puts out far less than ten lumens.

I made my own red LED torch in 1993 and have extensive experience using it. I have found it preserves my night vision.

I think my answer was fairly accurate given the original question I was answering and I did not say anything negative about the usefullness of lights with less than ten lumens output.

The active ingredient in rod cells is rhodopsin. When triggered, it bleaches in a very rapid chemical reaction. It is mentioned as being insensitive to red light such that this reaction is not triggered, however since it is 'acutely' sensitive at it's peak response frequency, a relatively low level of white light is enough to trigger this bleaching.

Here is a frequency response graph for the various human eye receptors - the dashed line is for the rods (rhodopsin):

If you can find some reputable reference that contradicts what I said, I would be happy to look at it.

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html

Rods Do Not See Red!

The light response of the rods peaks sharply in the blue; they respond very little to red light.

http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html#c4
Scotopic Vision

The Scotopic Efficacy curve was established in the same manner as the photopic curve. It's sensitivity is shifted however to peak at 507 nm, and decreases in proportionally the same manner as the photopic curve. This results in the scotopic curve reaching a relative value of zero sooner in the visible spectrum than the daylight curve. As a consequence of this fact, our nighttime vision does not see red!

http://en.wikipedia.org/wiki/Rhodopsin
Different wavelengths give different sensitivities, e.g., blue-green over orange. At the threshold for white light, only white is seen, but when the intensity is increased to a certain point, color is perceived. The difference between these is the photochromatic interval. Since the rods are extremely insensitive to red light, this interval is zero for red light, which means that sensation of color and light are at the same intensity. [4]

 

[PlayboyJoeShmoe]

Discovering GOOD multi level lights was a revelation!

The H50 on low is good as is the low of a Connexion.

And the lowest level of a D2Flex driving a P7 is mighty low!

 

[Sub_Umbra]

...Yes, in order for a light to preserve your night vision, it must be both red *and* very dim...

Emphasis mine.

Neither of those assertions are absolutely correct. They are generalizations. I will grant that they extremely popular myths, however.

Preserving night adapted vision is a very controversial subject. Some searching around (even just on CPF) will quickly dispel the myth that the only color that works is red. There many, many different methods of preserving dark adapted vision for different situations and most of them work even though they may involve beam colors of amber, green, cyan, blue, and even white. AND THEY WORK! This is very well documented on cpf and throughout the Web -- for those who will look. Nits may be picked endlessly by those who lack experience with these colors in various beam shapes but it's no secret. The methods are out there for anyone who will do the research. A broad range of effective methods will be found even if one confines the search to cpf posts. It is fortunate that those who do not understand this can not stop these methods from working for those that do.

As for the dim myth, that is a generalization that falls apart quickly with just a little thought. How bright your light is has no bearing on you dark adapted vision -- it's how much gets splashed back into your eyes that is the important factor. Few would challenge that viewing objects under starlight would consume little rhodopsin (visual purple), unless the starlight they are gazing under happens to be our own sun. While this may sound facetious, it helps make a valuable point that eludes most. In the confines of preserving dark adapted vision the only difference between the light from the stars in the night sky and the light from our own sun is how much of it finds it's way into our eyes. Contrary to very popular belief unimaginably bright lights may be used while preserving ones dark adapted vision.

First, use a tight beam -- the tighter the better. The tighter the beam the less light will be blown back at you. NOTE: when I say tight, I mean really tight -- not some tightish yet spilly beam that so many here at cpf claim to love. I'm not saying that there's anything wrong with that kind of beam, only that it will not work in this application. Be advised. Second, don't handle the light like an idiot. Care must be taken at all times to avoid any splash as much as possible. This will require both thought and practice. I kid you not.

An archtypicial example of the above technique is used on ships all over the world every night -- with one enhancement -- separating the light operator from the observer. With the darkness adapted observer on the bow a hideously bright multi-bazillion CP spotlight is operated from another location. It must be controlled very carefully. The sea is a great example because one is often trying to put eyes on something small and far away but unlike on land -- there is very little to reflect the light back into the observer's eyes and ruin his dark adaptation. Having done this many, many times I can tell you that this is real. Though it sounds counter-intuitive, the observer's dark adapted vision may be preserved even while using a multi million CP beam. The key would be that one has to know what he is doing.

Although ship's spotlights usually have whitish beams, it makes a good example because it is very easy to grasp. These techniques also work very well with cyan for those with experience in that color range. The same techniques work the same way on land but they require more operator skill -- whether the observer is also the operator or not. Again, the real catch is that, like so many other things in life, one must know what he's doing.

That's just one method of preserving dark adapted vision while using a brighter light than most will likely ever hold in their hand. There are more.

The most important thing about preserving dark adapted vision is the importance of keeping as little light as possible (whatever color is being used) from desensitizing the eyes. That is THE universal truth. Practice that one truth and you may twist and bend all of the other 'rules'. (This is how dark adapted vision may be maintained while using colors that are much easier to see with than red.)

 

[Bullzeyebill]

Sub_Umbra, in my example, going to the head, in my earlier post. I found that my 5- 10 lux flood beam light was easier on my eyes than my 100+ lux light. In that case I was using the light for short distances, a few feet, and the fairly tight 100 lux was bouncing back and I was seeing spots, not good for night vision maintenance.

Bill

 

[deusexaethera]

I made my own red LED torch in 1993 and have extensive experience using it. I have found it preserves my night vision.

I think my answer was fairly accurate given the original question I was answering and I did not say anything negative about the usefullness of lights with less than ten lumens output.

The active ingredient in rod cells is rhodopsin. When triggered, it bleaches in a very rapid chemical reaction. It is mentioned as being insensitive to red light such that this reaction is not triggered, however since it is 'acutely' sensitive at it's peak response frequency, a relatively low level of white light is enough to trigger this bleaching.

Here is a frequency response graph for the various human eye receptors - the dashed line is for the rods (rhodopsin):

If you can find some reputable reference that contradicts what I said, I would be happy to look at it.

When HID headlights first came out, I did a bunch of research on this topic, both to explain why I found HID light to be so blindingly painful, and also to petition my Congressman and Senator to impose tighter regulations to keep them under control. (I'm currently doing the same in regards to the ultra-bright red LEDs Toyota and Nissan are using in their taillights.) No disagreement here, but you'll notice the sensitivity curve for rhodopsin does overlap the frequency of light percieved as "reddest" by red cones, so sufficient brightness will still cause the bleaching effect you mentioned.

It is worth noting, however, that best brightness contrast is achieved using green light, so (as I recently learned) a far dimmer green light will be just as visible in the dark (and probably easier to read by) as a brighter red light.

 

[Flying Turtle]

That pesky spill light that gets in your eyes from Photons is the reason I really like the "covert nose" option. Just got an orange covert Freedom that is excellent for putting usable light only where you need it.

Geoff

 

[emr]

There are two types of night vision, corresponding with two types of eye receptors, rods and cones. The dark adapted rods work for peripheral vision and the dark adapted cones work for central vision.

For example, if the goal is watching stars at night, dark adaption of the rods gives sensitivity to dim light. However, since the rods work for peripheral vision, one must avert the gaze and view dim stars away from the center of vision. Rods have lower visual acuity, such as 20-200 vision, compared to 20-20 for cones. Also, rods give monochromatic vision.

Cones sense color and fine detail, and are located in the central region. To read a map or a star chart, you must use the cones. That means light for seeing details at night must be bright enough to use the cones.

Commercial pilots and submarines use dim white light to read details, while maintaining dark adaptation, because this allows seeing colors on the charts. Red light can allow seeing details, but the red light must be brighter than the white light. If red light is bright, this will reduce dark adaption. I know this is contrary to what is generally followed by star parties.

A flashlight with dim white light, or perhaps dim green light, allows reading detail with dark adapted eyes. A dim red flashlight makes reading difficult.

 

[Benson]

When HID headlights first came out, I did a bunch of research on this topic, both to explain why I found HID light to be so blindingly painful, and also to petition my Congressman and Senator to impose tighter regulations to keep them under control. (I'm currently doing the same in regards to the ultra-bright red LEDs Toyota and Nissan are using in their taillights.) No disagreement here, but you'll notice the sensitivity curve for rhodopsin does overlap the frequency of light percieved as "reddest" by red cones, so sufficient brightness will still cause the bleaching effect you mentioned.

Actually, that's not what's perceived as the "reddest"; that's what's perceived as the brightest (for a given light intensity) by the red cones. But because it also stimulates the green cones, it will appear quite yellow or orange, not red. The "reddest" perception occurs when only the red cones are stimulated; any longer wavelength after green drops out only becomes dimmer without gaining redness, but as you can see red is already appearing quite dim at that point.

A pure red, with no wavelengths shorter than 650nm, (e.g., a bright laser used in ceiling bounce) will not affect the rods, but with non-monochromatic light sources, you can have a red-appearing light with a long enough tail to have some impact on the rods -- in this case, brightness will matter a lot, especially since the poor red sensitivity means you need much more light to get adequate response.

 

[Bullzeyebill]

The irus is wide open in near or total darkness. This allows our cones to operate, or our rods, or both? If the eye registers color, then the rods are not operating? Is not the point of night adapted eyes to allow our rods to operate, so we can see our way about at night, and that the rods only operate at the lowest level of light output where colors to not come into play. So monochromatic vision is good, except for reading details, where contrast is needed. Pardon this confused post.

Bill

 

[Cheapskate]

Preserving night adapted vision is a very controversial subject. Some searching around (even just on CPF) will quickly dispel the myth that the only color that works is red. There many, many different methods of preserving dark adapted vision for different situations and most of them work even though they may involve beam colors of amber, green, cyan, blue, and even white. AND THEY WORK!

The preservation of night vision through the use of red light has a good basis in fundamental scientific principles as described in peer reviewed scientific publications. If you can show me some reasons, based on scientifically sound principles, why any of these other night vision preservation strategies should work, I might give them some credence, until then I will remain very sceptical of them.

The cyan explanation should be a doozy, as that would be a close match for the peak responsiveness of rhodopsin and should be the best wavelength for crippling night vision capability.

 

[deusexaethera]

That pesky spill light that gets in your eyes from Photons is the reason I really like the "covert nose" option. Just got an orange covert Freedom that is excellent for putting usable light only where you need it.

Geoff

I recently had good luck fixing the spill on a Peak Shasta flashlight by sanding the tip of the LED flat, because the tip was refracting light at an almost 90-degree angle. It might work on a Photon, too.

 

[PlayboyJoeShmoe]

I can't LIVE by red light. I do use red for midnight can runs, but dim white is more pleasing to my eyes!

 

[deusexaethera]

The preservation of night vision through the use of red light has a good basis in fundamental scientific principles as described in peer reviewed scientific publications. If you can show me some reasons, based on scientifically sound principles, why any of these other night vision preservation strategies should work, I might give them some credence, until then I will remain very sceptical of them.

The cyan explanation should be a doozy, as that would be a close match for the peak responsiveness of rhodopsin and should be the best wavelength for crippling night vision capability.

Or you can just TRY a green light and see for yourself. Experience trumps research every time, because what ultimately matters to you is what works for you. Maybe you have crazy mutant eyes that those peer-reviewed journals haven't taken into account; until you try it, you don't really know.

My father's minivan is exclusively lit with green LEDs -- it even has a couple of area-effect LEDs lighting the space between the two front seats -- and it has absolutely no effect on night vision. As long as the rate of light-induced rhodopsin decay doesn't exceed the rate of replenishment, you'll be fine.

 

[deusexaethera]

The irus is wide open in near or total darkness. This allows our cones to operate, or our rods, or both? If the eye registers color, then the rods are not operating? Is not the point of night adapted eyes to allow our rods to operate, so we can see our way about at night, and that the rods only operate at the lowest level of light output where colors to not come into play. So monochromatic vision is good, except for reading details, where contrast is needed. Pardon this confused post.

Bill

The dilation of the iris has no effect on which photoreceptors are working; there isn't a switch that turns off the rods and turns on the cones, or vice-versa. The key issue is that the chemical that rods use to detect light is also broken-down by light, whereas the chemicals that cones use to detect light isn't broken-down by light (or else requires much more light to break down). So, as the light gets brighter the rods become partially, then completely, insensitive to the light impacting them. This can happen by getting hit with a flashbulb on a bright sunny day, or by getting hit with a penlight in the middle of the night -- all that matters is the amount and color of the light entering the eye.

 

[emr]

The dilation of the iris has no effect on which photoreceptors are working; there isn't a switch that turns off the rods and turns on the cones, or vice-versa. The key issue is that the chemical that rods use to detect light is also broken-down by light, whereas the chemicals that cones use to detect light isn't broken-down by light (or else requires much more light to break down). So, as the light gets brighter the rods become partially, then completely, insensitive to the light impacting them. This can happen by getting hit with a flashbulb on a bright sunny day, or by getting hit with a penlight in the middle of the night -- all that matters is the amount and color of the light entering the eye.

It's a matter of degree. The sensitivity of rods does decrease when exposed to brighter light, but the rods and cones are always "switched on." Rods affect color perception even when swamped by the cones. Color perception changes with light intensity. The response of rods and cones is summed together and transmitted to the brain. It is the response of rods to blue that shifts the perception of color. That is why museum designers must carefully choose the color temperature of lighting to maintain the sensation of white. The rods affect perception of color; they don't turn off.