What is "useable light"?

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Why would you say that your flashlight still has some "useable light" in it?

1. I can still see objects 10ft or 5ft away.
2. I can still read newspaper with the light 1 foot away.
3. I can still see door's keyhole with my light 3 inches away.

Much have been said of a flashlight's useable light for xx hours but do we agree on what extent is light still usefull before the blackout stage.

Please feel free to add your definition of "useable light".

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Gransee

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It does not take much light to be "usable". Of course, for what tasks is it usable.

Pratically all LED lights have no problem in producing many hours of "usable light".

For me, "usable light" is more a question of "what level of light I would still use without changing the battery".

How many people regularly run their expensive LED flashlight to the point where there is no more light coming from it?

At what point with a particular flashlight do we feel we need to replace the batteries? I guess that would be the real "usable light" limit.

Peter
 

Silviron

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Certainly "usable light" is a matter of individual needs-

MY definition is: if it is bright enough to get around in a cave or mine without falling into a sinkhole or tripping over a boulder if you move fairly slowly and carefully.

Or finding your way around the house during a blackout without tripping over the kids toys scattered around the floor and allow you to find small items in a closet or drawer.

If a light does these things, I consider it "usable" / "useful". If a light will do this, it will also provide more than enough light to read by or enough to change a flat tire or find that loose spark-plug wire on a dark country road (etc).

Generally, in my experimentations, I find 3 LUX (measured from 1 meter) in a fairly tightly focused beam to provide this amount of light. 1 LUX in a fairly diffuse beam will do it too.

Of course if you are a cop on the "mean streets" or a "coon-hunter" (etc etc.) then, there is no way that this is enough light to be considered "usable". You need 150 to 300+ times more light....
 
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I asked the question because a flashlight can be rated as having 20 or 40 hour runtime but how much of that light is visually usefull, say ;

1. at its initial brightness/prime I can see objects and determine color 20 feet away.
2. after xx number of hours continous use I can now only see objects with the light 1 foot away.
3. and after xx number of hours of continous use my flashlight can only dimly illuminate my door's keyhole 3 inches away.

With regulated power LED flashlight, for ex: Arc-AAA's useable prime light is at least 95% true of manufacturer rated runtime. How about LED flashlights without regulators and rated by mfg. with a 20 hour runtime, how much of that 20 hour is visually usefull prime brightness light?

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The_LED_Museum

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Silviron:
Certainly "usable light" is a matter of individual needs-

Or finding your way around the house during a blackout without tripping over the kids toys scattered around the floor and allow you to find small items in a closet or drawer.
<HR></BLOCKQUOTE>

The term is highly subjective, but I find the above definition applies to me more than any of the others presented thus far.

I do not camp, climb, cave, or hike.
I do not hose down criminals with my colt .45.
I do not repair balky car engines on the side of the road at 2am.
I do mill around the house at night.
I do have to avoid pet's tails, boxes, and furniture at night.
I do often need to search through boxes, closets, and drawers.

This almost entirely defines my threshold for usable light. At these light levels, you could also read while sitting on a toilet without ruining your night vision, and make your way to the fridge or repeatedly check switches & door locks at night if you're the obsessive type.

$0.02
 

WarrenI

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So the song goes, "What is "useable light"? It's more a matter if you are happy with your light and what you paid, then it should not matter that anyone should classify your light to produce less usable light, or you could have spent more to get a more usable light.

If it's in regards to beam quality, my preference is to not have a very narrow beam with little spill. I like a medium to broad center beam with a gradual spill. With this type of beam, you would be able to see much in front of you without having to redirect the beam every second. This is my choice, but it may not be yours. Especially for fishing, my preference would not work as they pretty much need a light that cast a directional beam to penetrate the water.

When you first bought your light, you were probably impressed how bright and usable it was. I don't think you would have been impressed if you could only read a newspaper with it. Realistically, I do not think this is a good gauge to say that the light is still usable. My Arc-AAA (regulated) shines easily to 15 feet and I plan to change the battery as soon as it kicks to the "moon" mode. My LightWave4000 (unregulated) shine easily to 40 feet and I plan to change the batteries when it can barely reach 20 feet (uneducated 50% light loss). I expected each of these lights to give me resonable illumination for what I paid for them. If I needed a light to read papers, I could have used some of my freebie light I have lying around.

Also, let's not forget the construction and the usability of the light. Does it suit your purpose? It could have a great beam, but have no guts to survive anything or very awkward to use. Let's face it and be a little macho, sometimes we want it to look dam good and impressive too.
 

Silviron

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by 2d_edge:
I asked the question because a flashlight can be rated as having 20 or 40 hour runtime but how much of that light is visually usefull, say ;
......-
<HR></BLOCKQUOTE>

That is why when I get my LED light website up and running (soon, I promise soon...) the lights I have for sale will include extensive longetivity - and brightness test results (just like on the conversion stuff I HAVE posted).

I don't know why the big manufacturers / dealers don't provide the same sort of info- It would be just a tiny expense comparatively. Maybe they just don't want to confuse the non-flashaholic hoi-polloi.

Or more likely the true results would cut into their marketing hype??
 

Harrkev

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There DOES need to be an objective defenition of "useful" simply to be able to compare manufacturer's claims.

For a Photon, useful might consist of being able to read a newspaper from 1' away. However, it would be absurd to use that definition for a Surefire.

Perhaps a good start at a defenition might be:
Code:

While the light might still be useful for a while longer after that, such a defenition would at least guarantee that all manufacturers are on the same page

It could also be agrued that you would buy a particular light because you needed that particular level of brightness, and at half-power (3dB down, for the engineers), it is no longer suitable for the intended purpose. Then, if you buy a light that is TOO bright for your use, then you will get more life.

This is just a suggestion. Feel free to shoot it down.
 

Spidey82

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How bright is the aaa arc in moon mode??
i don't think my white photon is usefull after 1 hr.
after a few hr, i think u can only light up a key hole a few cm away.
 
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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Gransee:
At what point with a particular flashlight do we feel we need to replace the batteries? I guess that would be the real "usable light" limit.<HR></BLOCKQUOTE>

I change flashlight batteries for the purpose of maintaining certain level of brightness that is usable to me from a particular flashlight. Pretty much the same reason I replace a degraded bulb or lamp with the same "watt" rating to maintain a certain level of brightness in the house.

Running flashlight to the point of blackout will only happen if replacement battery is unavailable.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by WarrenI:
When you first bought your light, you were probably impressed how bright and usable it was. I don't think you would have been impressed if you could only read a newspaper with it. Realistically, I do not think this is a good gauge to say that the light is still usable. <HR></BLOCKQUOTE>

Right, there has to be a certain acceptable level of usable brightness from a particular flashlight. For Surefire or LW4000 only capable of brightness, or 80% of its xx number of hours of brightness rated by manufacturer, to the level of reading a newspaper 1ft away is not what the flashlights are designed for and there's got to be an anomaly or something wrong somewhere for the flashlights to behave this way. On the other hand will it be okey for a Photon for 50% of rated xx hrs. brightness to get down to the level of only illuminating a newspaper 1ft away as acceptable level of brightness because it is not designed for and advertised to be able to outshine or comparable to the brightness use of Surefire and LW4000.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Harrkev:
1)Insert new batteries and measure light output after three minutes (let the surface charge dissipate).
2) Usable life will "end" when light output is 50% (or maybe 33%) of initial reading.
<HR></BLOCKQUOTE>

I tend to agree with Harrkev. Beam brightness will degrade as battery runs out of juice. Flashlight use is not measured by how much juice battery still has left in it but how close is beam brightness to its prime brightness.

How do we do that? Measure with a lightmeter or current/volt meter and graph flashlight's beam output.

Suppose a flashlight started with a current reading of 200ma, is it safe to say that when it reaches reading of 100ma light is no longer usefull? I mean will the numbers (mA or lux) correspond with my visual perception?

I guess it's going to be a case-by-case basis depending on flashlight's model.
smile.gif



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PeLu

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by 2d_edge:
Why would you say that your flashlight still has some "useable light" in it?
<HR></BLOCKQUOTE>

When yu use your light in a complete dark environment (cave or mine) even a tiny amount of light might be useful.
When you are in trouble (or somebody who is with you), you usually have to wait for a very long time for rescue.
Injured or trapped people are very often in a bad mood and even a little light might help them mentally. And if you are in a cave for some days, you can navigate around with very, very few light. I have one of these betalights which contain tritium and have a half life of some 11 years (meaning the light output is cut in half every 11 years). It was good for looking at a map from some 10cm distance (light to object). After beeing in cave for several days, it was easy to walk around with it and do simple tasks. It would also be possible to fix another light (usually a carbide lamp) with it.

For moving out a cave, it depends very much on the kind of it. For most TAG caves, little light is needed to do that. In alpine caves, it is usually more complicated. And in some caves you have big rooms where you have to look for the exit. Your 'useable' light will be a much brighter one. And also the surrounding walls have a very big influence. Yesterday in an ice cave I had to use the high setting most of the time. Ice tends to 'eat up' the light. Difference in between nice white cave walls and black lava tubes can be easily 1:10 (ask a cave photographer!)

I'm referring to caving because it is the most serious use for my lights.

I tried an Arc AAA as an emergency light (it is easy to mount it on your hardhat's side) and it turned out that it is good for almost any cave.
 

PeLu

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Gransee:
For me, "usable light" is more a question of "what level of light I would still use without changing the battery".<HR></BLOCKQUOTE>

For example I change my ActionLight's battery when it does not drive the high mode any more. Exactly when I came 'home' after this trip.
Not because 'normal' or 'low' does not give useable light, just because I know that the battery is now almost empty (only 10% or so left).
 

PeLu

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Harrkev:
Perhaps a good start at a defenition might be:
Code:
<HR></BLOCKQUOTE>

A very good approach, but I want to add also the hours to the next 50% and so on. Meaning I want to have a row of numbers like:
1/3/6/8 hours, meaning after one hour the output is 50% of the initial brightness, three ours later it is 25%, six more hours it is 12.5% and so on.
Of course a diagram would be the perfect solution.

AFAIK changes an Arc AAA's brightness about 1:2 before it wents into 'moon mode'. This is a very fair solution. Even a LuxBrite changes a little over the batteries useful life, ActionLight, Headlite III or Lupine are very stable (is that worth the price? decide it yourself), also the Matrix should be (have to get one back for testing).
 
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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by PeLu:
When yu use your light in a complete dark environment (cave or mine) even a tiny amount of light might be useful. <HR></BLOCKQUOTE>

I haven't gone caving or been to a cave. Just a curious question Pelu... would a CMG Infinity's (white LED) lightbeam with 40 hr burntime be sufficient as primary light for caving?

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by PeLu:
but I want to add also the hours to the next 50% and so on. Meaning I want to have a row of numbers like:
1/3/6/8 hours, meaning after one hour the output is 50% of the initial brightness, three ours later it is 25%, six more hours it is 12.5% and so on.
Of course a diagram would be the perfect solution.
<HR></BLOCKQUOTE>

I agree. I might do time-lapse photos of flashlights to show both lightbeam and current reading at the same time in a picture.

This way I can show a beam brightness and current (mA) reading corresponding to lightbeam's level of brightness in a 3 minute or half-hour interval. We will be able to see the current reading with every frame of lightbeam photo.

Oh how wish I bought the laptop instead of this bulky tower.

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PeLu

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by 2d_edge:

I haven't gone caving or been to a cave. Just a curious question Pelu... would a CMG Infinity's (white LED) lightbeam with 40 hr burntime be sufficient as primary light for caving?
<HR></BLOCKQUOTE>

Only for very tight and simple caves. For 'usual' ones (what is usual?) you will have to move pretty slow. With an Arc AAA I may move almost normal in caves I know well. But it is much more exhausting (mentally) using a dimmer light. And when you are tired you need more light (your eye seems to be less sensitive and the brain's data processing is slower). And especially when you are exhausted it is very nasty when you hit a rock with your knee or tibia (shin bone).
One big factor is also personal preference. Some people say they need at least 48 Nichia LEDs for a serious caving light, overs just use a single one.
One time I made my way out from an underground camp back to the entrance (some 5 hours for me) with a single led running at 70mA (with a reflector and a good heat sink at 4°C!), but I know this way well.
For climbing up a rope you need no light at all.
It is interesting: Since I have a very constant light, I can tell the difference you own condition makes. In former time, the light output was varying soo much that everything else was negligible.
 
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