Where do you think we'll top out with this lumen thing?

:touche:

It would be cool if we can get to the point where we can start an actual fire with a flashlight beam, but don't know if we'll get that far

Dr. Tweedbucket said:

:touche:

It would be cool if we can get to the point where we can start an actual fire with a flashlight beam, but don't know if we'll get that far

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No it's been done, incandescent bulbs with 100 watts 2x18650 batteries and a good throwing reflector and you have over 280℉, well enough to light a fire with only 1,500 lumens.

Also, if you take a typical1,000 lumen flashlight LED, and hold it ten feet away, and use a magnifying glass about 5" from some paper, and it should be about 500℉, enough to light most kinds of paper.

Holy crap!!:sick2:

What is this "top out" you speak of? It sounds limiting..

RickZ said:

Also, if you take a typical1,000 lumen flashlight LED, and hold it ten feet away, and use a magnifying glass about 5" from some paper, and it should be about 500℉, enough to light most kinds of paper.

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Wonder how many will try this to see if it works..

I think that the upper limit for lumens for a flashlight with extended battery carrier/8 x 18650 in a size not much bigger than a TK75 will be about 35,000 lumens for the next two years, until new technology appears to get us past that.

How can we ever forget this goodness.
http://www.candlepowerforums.com/vb/showthread.php?368370-Fire

considering that we have 4x18650 lights that tops out at over 6000 lumens I'm guessing no. lumens will top out only when the batteries necessary to power it for a practical period of time becomes too heavy.

I think pushing past 20,000 lumens from leds is going to depend on heat management and being able to maintain reliability.

Let's assume that we can get max. 75W (20 A draw) from one 18650 battery and 100% luminous efficacy then we can get a theoretical 75W *680 L/W = 51000 lumen per battery. Now lets slap some efficiency coefficients on that: Let's go for 10A draw = 50%, 80% for the electrical/electronic system and somewhere around 40% for the luminous efficacy then we end up at 8000 lumen for a flashlight with one 18650 battery. This would be my bet for a small flashlight in 5 years . That's still 25 W of heat to get rid of - but hey it's the future we are talking about.

MAD777 said:

I think pushing past 20,000 lumens from leds is going to depend on heat management and being able to maintain reliability.

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+1

Vinh has done the 21k in the tk75 which is astonishing..............

The hardest part is the HS side allowing decent run times.........that is the challenge other than HUGE mass..........

As for topping out............never imo, there will always be a demand for higher lumens,regardless of how short run times. As LED's become more advanced,even now with the xhp70 which is good for 5k, what will next year bring........7k or more. Then multi emitters ,potential is there...........just making it actually usable for longer than 30's at a time.

I think 3-4k is the magic number right now for high output and sustainability.........by that i mean for 5-10mins+ in larger lights like the x60 and in cool outdoor conditions the tk75 sized light. After that its cell life, even with 4 or 6 cells inside,sustaining over 4k lumens for much over 1hr is difficult without extra extensions. Well i guess thats not an issue if the higher lumen requirement is needed anyway...........

I thought last year we were getting close or peaking in lumen/output but this year with MKR and xhp70 lights, this has give me greater confidence for next year

I would like to see 4-5000mah 20-30a cells now in 18650 flavour..........maybe a way off on that one though!!!

It's all about heat and battery.

Not long ago a flip cel phone with enough memory to hold 1500 numbers and a few dozen thumbnail size photos that gave you 2 hours of talk time was a marvelous thing.

Now a phone with quad core processor, 16gb of ram that gets 4 hours of internet browsing is the norm.
Mainly thanks to battery tech and heat management (through efficiency).

That's the future imo...the efficiency end. Way more light using the same (or less) power.

RickZ said:

Also, if you take a typical1,000 lumen flashlight LED, and hold it ten feet away, and use a magnifying glass about 5" from some paper, and it should be about 500℉, enough to light most kinds of paper.

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My BS detector went off, so I decided to try it. As expected, it just turns a nice reflector light into one of those cheap optic throwers with the square LED hot spot. Warm to the hand, but less warm than if you just held your hand closer to the flashlight without any magnifying glass.

IIRC, you can't magnify an image to be any hotter than what the surface temperature of the source object is. For example, you can't magnify the sun hotter than 5500C. I don't know what the surface temperature of an LED is, but probably not hot enough to burn paper.

WalkIntoTheLight said:

I don't know what the surface temperature of an LED is, but probably not hot enough to burn paper.

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The infrared heat emitted from LEDs is negligible, it might be hot enough to burn paper provided the paper used possesses the ability to absorb ALL of the light produced by the LED, including the wavelengths of the visible spectrum. Because of this difference, LEDs cannot be compared to a 1000 lumen incandescent.

Though someone from Germany did manage to scorch paper using MCEs and Fresnel...

Data sells a kit for firestarting using his Spy's... See "Fire" thread in the Cool Fall subforum.

Lets just discuss 101 ways the kiddys and kooks can start fires with flashlights in this thread, why don't we?

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WalkIntoTheLight said:

IIRC, you can't magnify an image to be any hotter than what the surface temperature of the source object is. For example, you can't magnify the sun hotter than 5500C. I don't know what the surface temperature of an LED is, but probably not hot enough to burn paper.

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Many years ago when I was researching ablative materials, I had samples heated to 6,000F using a solar furnace. The heat generated was almost instantaneous due to the focusing mechanism used.

This solar furnace was located in the Pyrenees mountains in France. I'd hate to have the job cleaning all of the mirrors.

http://www.pyrenees-cerdagne.com/en/science-and-energy

SemiMan said:

LEDs are not processors. One has a hard physical limit, ones does not ... at least not yet.

What is likely to be the hard limit is optical transmissivity and the heat generated from such ..... magnetic/efield optics aside of course. Even if you get super efficient LEDs, the light has to pass through or reflect off something ... and we are still talking hand-held right?

In a practical hand-held light, I would expect to top out at 90-95% total efficiency.

Let's say you can dissipate, for short periods of time, 50Watts, that means 500-1000 watts to the LED.

Let's assume 400 lumens/watt at the LED .... so 200-400,000 lumens max.

A more realistic shorter term (5-10 years) would be 75% efficiency, 50 watts thermal, and 350 lumens/watt or 70,000 lumens.

Again, talking something the size of maybe a 3 D cell flashlight.

Semiman

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My point being that once upon a time (not long ago) a high efficiency 65 lumen incan ran for an hour on a pair of 3 volt batteries in sync.

Now with a not so modern LED 220 lumens for a couple hours on a single aa is not a big deal...

Yeah I know LED's aren't processors...but who's to say LED is the final technology?

Once upon a time the vinyl record was replaced with the 700 mb cd...but now the pinky nail sized memory card can do (last time I looked) 32 gb.

Again...as technology changes there's no telling what's possible.
http://www.zdnet.com/article/goodbye-leds-hello-plastic-bulbs/
Fipels...