# Trying to visualize 2 lumens and 1/2 lumen.



## gcbryan (Mar 26, 2010)

I've read everything I could find but after wading through all the terminology, examples, math, etc...I still have this question.

Perhaps someone has a good example to help me visual this. I've read all about one candle one foot from a one square foot piece of paper but I still don't quite have my answer.

Specifically, I have a Proton Pro (fairly new so I think it's a little different than older ones as far as max output). I'm guessing max output is around 100 lumens. I think older ones were around 80 lumens and newer ones around 100 lumens or so (I'm not sure about this).

It's the low end I want to understand both for the main white led and for the smaller red led. I'm posting in this forum because it really isn't about the Proton Pro. I'm just using that as a reference point since I have one.

At night with no lights on in the house I used the bathroom shower as a test area. I couldn't see at all when the Proton Pro was off. I ramped the main white led to it's lowest setting and I could see very well. I can walk around a dark house with no problem as well.

It's supposed to have a very low low mode but I don't know if it's 5 lumens, 2 lumens or less than one lumen. What reference can I use to determine this?

Also, when I ramp the red led to it's lowest level I can't see details very well. I can tell the light is on but have to move the light around to really make out my surrounding even when it's a white shower wall a few feet in front of me. If it was totally dark in the house (rarely is) it would be hard to walk around at this output level unless my eyes were totally dark adapted. What reference can I use to determine what this very minimal output level is?

My guess from the reading I've done is that perhaps the white led at the lowest level is 2 lumens and the red is 1/2 lumen.

How can I come to a more accurate educated guess (not using light meters or any equipment)?

Someone with more knowledge than I must know what lumen level the red led in the Proton must have to be at given my description of what I could see (human lower threshold) and someone must also have an educated guess as to what the white led must be outputting given the source (Proton Pro) and my description of what I can see.

Anyone?
Thanks.


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## Burgess (Mar 26, 2010)

I'm gonna' give you MY judgement in answering your question.

Since i myself have an LRI Photon Proton Pro.


Lowest level of White emitter is WAY less than 1 Lumen.

Based upon my rather crude, yet usable measurements,
i would guess-timate this to be 0.2 Lumens.

That is, one-Fifth of a Lumen


This is *Roughly* equal to Moon-mode on my 4Sevens Quark flashlight.
(XP-G R5)


As you have witnessed, this level of lighting is indeed quite adequate
for dark-adapted eyes, in total darkness. :candle:


Hope this is helpful to you.

_


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## gcbryan (Mar 26, 2010)

What is your guess for the low of the red led?


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## Burgess (Mar 26, 2010)

unable to *Measure* the Red at Lowest output.


If i *had* to GUESS . . . .


perhaps 0.005


Understand, that's pretty much just a Wild-***-Guess ! ! !

:tinfoil:
_


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## gcbryan (Mar 27, 2010)

If all this is correct then you'd have to conclude that 1 lumen is pretty bright!


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## Burgess (Mar 27, 2010)

In *Total Darkness*

with *Dark-Adapted eyes*

1 Lumen is surprisingly adequate.


Provided you are in a non-threatening environment.


:candle:
_


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## axd (Mar 29, 2010)

Interesting thread because I am facing a similar question with tritium lights (not the locator lights, but personal lights) which also operate in this low end. Whoever has tritium lightsources (beta light, *Luce De Notte*, ...), please have a look at this related thread.

Maybe there's an additional complication when attempting to express "measure of light" (brightness, luminance, ...?) in case of monochrome light (red in this case, or often green in the case of tritium).

About the problem of discerning details under very low lighting conditions, the eye might have an issue (but maybe I'm confusing with purkinje effect, or maybe that IS what I'm trying to say; not sure).

I remember of a light experience with a sliding wall between two light sources: to estimate the brightness of a light (compared to another light), the wall has to be moved to a place between the two lights so that both sides appear with same brightness, from which a relative intensity can be measured.


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## gcbryan (Mar 29, 2010)

axd said:


> Interesting thread because I am facing a similar question with tritium lights (not the locator lights, but personal lights) which also operate in this low end. Whoever has tritium lightsources (beta light, *Luce De Notte*, ...), please have a look at this related thread.
> 
> Maybe there's an additional complication when attempting to express "measure of light" (brightness, luminance, ...?) in case of monochrome light (red in this case, or often green in the case of tritium).
> 
> ...



I think you are right, it is probably had to estimate the lumen output of a red light in comparison to a white light source as details will be lacking with red even when it is at a comparable output level with a white light (I think).

However, in the case of this particular flashlight that we were describing it is clear that the red led gets much lower than the more powerful white led. Even when you discount not being able to pick up details with the red it's still dimmer. It's hard to see...not just details but just seeing period!

Thanks for the link. That is a good description of why and how red lights work to preserve our night vision.


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## MD Light Guy (Apr 17, 2010)

I'm no expert, but a while back I had a class on lighting and it's important to note that when the human eye observes two light sources of equal lumen output, one "white" and one "red," the red one will most definitely appear to be dimmer. It's simply that the human eye is less sensitive to light at these wavelengths. Similarly, "green" light actually appears to be brighter than it's actual lumen rating (human eye MORE sensitive to light at these wavelengths.)

Some theorize that humans became adapted to see these "green" wavelengths as an ability to find plant life for food.

Trying to "judge" the lumen level of different wavelengths of light with the human eye is a futile task. While our eyes can do some incredible things, they are easily "tricked."

Not that this helps answer your original question very well, but just some additional food-for-thought, I guess.

Jason Herbert
SkyTech Productions
www.searchlights.com


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## paulr (May 12, 2010)

If anyone is still reading this and cares: 

1) the most popular flashlights of all time, the 2aa minimag and its penlight predecessors, had output of about 5 lumens.

2) the CPF'er classic lights Arc AAA and CMG Ultra-G were about 3 lumens. The CMG Infinity was about 1 lumen. Typical "Fauxton" keychain coin light is about 10 lumens when the batteries are brand new, but after just a few minutes of use drops to around 3 lumens and most people don't even notice the drop.

3) If you have a 5 lumen keychain light and want to experience 2 lumens, just cover the bezel a little over halfway with your finger. If you want to experience 0.5 lumens, cover 90%. Really, 0.5 lumens is enough to read with (hold light close to page), walk around in the dark, etc. 0.1 starts getting pretty dim though.


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## gcbryan (May 12, 2010)

paulr said:


> If anyone is still reading this and cares:
> 
> 1) the most popular flashlights of all time, the 2aa minimag and its penlight predecessors, had output of about 5 lumens.
> 
> ...



I started this thread a while back and I did learn more and was able to come to grips with 1/2 lumen vs 2 lumen.

It also has a lot to do with how it's focused. I have a Proton Pro which gets anywhere from .2 to .5 lumen (depending on who you talk to). Actually I think .1 lumen would probably be fine as long as it was focused in a small hotspot.

Conversely .5 lumen that was emitting in a 360 degree range would seem a lot dimmer than when it is in a tightly focused beam.

If anyone hasn't thought in these terms at all I can definitely say that 1 lumen focused into a hotspot is bright when it's completely dark but it's quite noticeable around the house even when it's light and you shine it in a shaded corner.

The scientific answer as I recall was to equate 1 lumen with 1 lux at 1 foot. A single childs birthday candle puts out approximately 1 lux on a white piece of paper 1 foot away and 1 foot square.

If you can imagine the amount of light just at that distance and just on that 1 foot square piece of paper that's one lux (at that distance) and it's also 1 lumen.

So one birthday candle is more than 1 lumen because the light is going out 360 degrees but it's still a helpful visual image. The other thing, which is obvious of course, is that when it's completely dark any light is bright!


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## paulr (May 12, 2010)

The definition of a lumen is 1 standard candlepower in a solid angle of 1 steradian. Since there are 4*pi=12.56 steradians in a sphere, that means that a standard candle is 12.56 lumens. A child's birthday candle might be 1/4 of that or thereabouts, I don't know.

If you have a 1 lumen light like a CMG infinity, bouncing it off the ceiling makes more than enough light to see around the room once you're a little bit dark adapted. I still keep my original 3 lumen Arc AAA next to my bed and it's the light I usually use to find the bathroom at night.

I saw an estimate that the lowest white level of the Proton Pro was about 0.03 lumens. For various reasons that doesn't make so much sense and I'd guess it closer to 0.1, but I've never tried one. I actually might buy one soon; I was just thinking about it and came across this thread while searching for posts about it.

The Photon Freedom is probably about 0.01 lumen at its dimmest, and it's still bright enough to read or walk around a dark room with. The Rigel Skylite (astronomy light, adjustable) probably also gets down into that range.

Remember also that human night vision evolved so that humans could walk around by moonlight without bumping into things. Night vision of cats is even more sensitive than humans' since they have to catch mice in the dark, not just avoid bumping stuff. Cats have a special structure in their eye called the tapis ludicum for that purpose.

The albedo of the moon is about 0.12 so you can figure out the illumination level from the full moon, half moon, etc. based on moon's diameter of 2160 miles and distance to earth of 238,000 miles. Actually there is a nice table here:

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

Full moon on clear night = 0.27 lux = 0.025 lumen per square foot approx.


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## gcbryan (May 12, 2010)

I find it an interesting subject. I have both a Proton Pro and a cat. 

I got into the tub, closed the shower curtains and turned off all the lights one night to really checkout the Proton Pro on the lowest of the red levels.

On white it's as you said. I can hike in the woods with it using the white level on low. With the red I got it so I could barely see the projected beam on the wall and the end of the tub where my feet were. My cat jumped up onto the tub while all this was going on and I had read where they could see 6-9 times better at night than humans (no surprise) and was just wondering what the light level looked like to him as I could hardly make out my feet...and he fell into the tub!

So, yes they can see much better than humans but they have their limit as well. I'm sure it had more to do with peripheral vison and not seeing that the edge of the tub was wet and slippery but that's sort of my definition of dark...when cat's have trouble seeing.


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## paulr (May 12, 2010)

I wonder if cats have poor visual sensitivity at red wavelengths. Nighttime illumination is mostly in the blue-green so that's where the most sensitivity is.


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## gcbryan (May 12, 2010)

paulr said:


> I wonder if cats have poor visual sensitivity at red wavelengths. Nighttime illumination is mostly in the blue-green so that's where the most sensitivity is.



I think you're right. I'm not a hunter but I've read about hunters using red light (I think) because some animals don't seem to notice it.


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## Byydo (May 27, 2010)

paulr said:


> I wonder if cats have poor visual sensitivity at red wavelengths. Nighttime illumination is mostly in the blue-green so that's where the most sensitivity is.



I'm not a cat expert but I do seem to recall that most cat eyes seem to glow a bluish green when you shine a light at them. This might suggest that the tapetum reflects mainly those wavelengths, so the cat's light multiplying mechanism would presumably work best on blue-green light.

Thinking about it, the only source of dim red light at night would probably be fire, and the main creatures with an evolutionary advantage to seeing by firelight would be human beings. 

Therefore it wouldn't surprise me if a lot of animals with good night vision might actually have pretty poor red vision at night. After all, there is a limit to the photoreceptor density per area on a sensor (retina) and so I would expect nocturnal animals would have eyes optimized for common wavelenghts.

But again, I'm not an expert.

I find that even my cell phone LCD, which puts out way more light than my preon on low, is like shooting off a signal flare if I light it up in the middle of the night in a dark room.
Walking around the lit-up city at night though, my tk-40 barely seems like a candle.


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