# Lumileds announce new K2



## HumanLumen (Nov 15, 2007)

See the website!
Only thing is, they quote 160Lm at 1000mA and bang on about the ability to be driven at 1 amp continuous - who cares? - The R2 bin crees achieve this at 160 Lm at 550mA. At 1A it will achieve 250Lm. Even if you doubt crees abaility to live constantly at 1A, it doesn't matter as you can achieve the same output at lower current.
When you look at the datasheet, there are higher bins availble - ones that achieve 200Lm at 1000mA - why don't they shout about those? We know that higher flux bins have been available (see Rebel).
I have always supported Lumileds in threads when it seemed that the pro-cree'ers were out in force, but Lumileds do seem to shoot themselves in the foot with partial releases and datasheets that say 'we are the best' with data that indicates that they actually loose out in the real world. Only if they launched the 200 bin now and you drive it at 1.5A would you see an advantage.
This is a quick rant on my lunchtime and not the best put together discussion, but I am waiting for somthing from Lumileds that does not appear to be surfacing....


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## HumanLumen (Nov 15, 2007)

Another thing - just looked at the data sheet and the output at 1000ma looks about 2.22 x that at 350mA - same as cree. What happened to that anti- droop technology that was going to be incorporated by Q3 of this year (July-september)? Has that found its way into another product??


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## monkeyboy (Nov 15, 2007)

The "K2 with TFFC" may not be on par with the best Crees but still seems pretty interesting to me. Remember 200lm at 1000mA is the minimum spec (for the 0200 product).

Typical flux:

95lm @ 350mA
170lm @ 700mA
275lm @ 1500mA

This still makes it the brightest single die LED available and is not that far off the Cree and SSC LEDs at lower drive currents. I wonder what happened to the 500lm LED that they achieved in the lab? Hopefully it won't be long before we see one of those.

I see they're also offering a star base

Oh yeah, well spotted BTW. I think you're the first.


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## evan9162 (Nov 15, 2007)

We've known these have been coming for months (I reviewed a pre-production sample here: https://www.candlepowerforums.com/threads/171365)

Lumileds has been dragging their asses getting anything new out, it's about bloody time we see some kind of movement from them.

One interesting thing is the 5.5C/W thermal resistance, which is very good, which means this part could be quite suitable for high current or high operating temperatures.

Future only has the 160 and 180s listed, but both are in stock - at $5.12 and $5.60 each respectively.

It's a shame Lumileds isn't more aggressive at getting high brightness parts out, but the lack of available 200 and 220/240 parts mirrors the lack of availability of 90 and 100 lumen rebels - the demand for 100 lumen rebels is so great that I can see all high bin dies going to those lines instead.


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## Lightingguy321 (Nov 15, 2007)

Evan, do you think that it would be worth it to start buying K2s (the new TFFC obviously) since I do not have anything better than a U-bin K2 any way? These look promising but I can't say if these will be better than take 1 of the K2.


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## evan9162 (Nov 15, 2007)

Really depends on what you're doing. If you're looking for a direct drop in, it would be a reasonably nice upgrade. 

What kind of application are you talking about?


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## Lightingguy321 (Nov 15, 2007)

Drop in for my junior Luxeon which is still running a U bin K2. Also possibly using them in home lighting on 6x arrays.


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## evan9162 (Nov 15, 2007)

Lots of factors to consider, even for both cases

For the first case, You could use a Seoul P4 which has a very similar package as a K2, would be a bit brighter, but might not focus as tightly due to the P4 having a slightly larger source volume (even though the beam profile is the same). However, one thing to consider with the P4 is that the slug is connected to the positive power lead, and if you don't isolate the slug of the Seoul properly, you could create a short.

Using an XR-E is also an option, but packaging and beam profile differences may be significant enough to render it not a viable option.


For home lighting, beam profile and lumen/$ are likely the more dominant factors to consider. It may be a matter of personal taste which one you choose.

In both scenarios, cost and availablility are also factors to consider.

So like with most things, there is no one easy answer. Choosing one of the new K2s to put in your jr Luxeon is an easy upgrade option, but might not be as bright as it could be with competing LEDs. Depends on how much you want to experiement to see which could be the optimal solution.


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## saabluster (Nov 15, 2007)

monkeyboy said:


> Typical flux:
> 
> 95lm @ 350mA
> 170lm @ 700mA
> ...


I'm sorry but this K2 sucks. The R2 cree is doing 275 lumens at 1000mA. And thats before you overdrive it(which it can handle no problem).


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## evan9162 (Nov 15, 2007)

saabluster said:


> I'm sorry but this K2 sucks. The R2 cree is doing 275 lumens at 1000mA. And thats before you overdrive it(which it can handle no problem).



Wow. That's such an in depth and detailed analysis of the situation. Guess there's no reason whatsoever for anyone anywhere anytime to use one of these in any scenario. Period.


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## Calina (Nov 15, 2007)

Those new K2 probably have the best lumen/$ ratio although I didn't really do any calculation.


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## Anglepoise (Nov 15, 2007)

Evan,
Am I correct in my assumption that the 'New' K2 should be a pretty good mod to an existing Lux III setup. No machining of reflector needed.


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## evan9162 (Nov 15, 2007)

I can't guarantee that. I haven't done extensive comparisons between the old/new K2 and a Lux III in terms of die height. 

I could do that later today - attempt to get some pictures of the 3 LEDs side by side to compare die heights


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## monkeyboy (Nov 15, 2007)

saabluster said:


> I'm sorry but this K2 sucks. The R2 cree is doing 275 lumens at 1000mA. And thats before you overdrive it(which it can handle no problem).


 
Not a chance that the R2 will do 275lm @ 1000mA and however much the cree can be overdriven, the K2 can be overdriven more with its higher junction temperature


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## frenzee (Nov 15, 2007)

monkeyboy said:


> Not a chance that the R2 will do 275lm @ 1000mA and however much the cree can be overdriven, the K2 can be overdriven more with its higher junction temperature


 
I have to say a 5.5º thermal resistance plus a 185ºC Tj is quite impressive, but there might be more to it than that. For example the pad size - in which Cree has an advantage -, bond wires, die composition and the so called "droopiness" factor. I don't think we'll know for sure until someone runs full battery of tests on both under real world conditions.


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## SemiMan (Nov 15, 2007)

Does anyone get tired of the knee jerk reactions?

Cree:
- More efficient (obviously)
- Isolated package (so much nicer to use)

K2:
- Wide lambertian beam pattern which is better for reflectors
- More even phosphor coating (which can be nice)
- Better thermal (but offset by lower efficiency)

The Cree can be overdriven for "short" periods of time...fine for flashlights, but not in the real world where things need to last. They only rate the life at a low die temp. In long life applications (my day job), that becomes an issue.


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## evan9162 (Nov 15, 2007)

As promised, die height comparisons:

Lux III vs. Original K2:






And Lux III vs. TFFC K2:






As you can see, even the original K2 isn't a direct replacement since the die is a bit lower. The new TFFC K2's die is even a bit lower.


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## Calina (Nov 15, 2007)

Technically with the thin film more photons can escape the die therefore less heat is generated inside the phosphor coat but it is so thin that I wonder if we should start to worry about degradation and phosphor life.


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## jtr1962 (Nov 15, 2007)

I'm not overly excited about this. It has nothing to do with the somewhat lower output relative to a Cree. Rather, it has everything to do with Lumiled's spotty track record of actually delivering product. The Rebel-100s actually seemed very nice, were competitive with Cree in terms of output, and I think the color consistency was better. They beat Cree hands down on price. Only problem is they're not available, at least for now. The new K2 might be worth a look in certain situations where lumens per dollar or perhaps tint consistency count for more than sheer efficiency. However, if it's not consistently available I wouldn't use it in a product.


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## evan9162 (Nov 16, 2007)

The 160s and 180s are available today (I ordered a few for evaluation).


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## saabluster (Nov 16, 2007)

evan9162 said:


> Wow. That's such an in depth and detailed analysis of the situation. Guess there's no reason whatsoever for anyone anywhere anytime to use one of these in any scenario. Period.



I'm glad you agree.  Seriously, I'm sick of them dragging their feet. I want the goods. This doesn't come close to the cree for what the entire purpose of their existence is. To create Light. The K2 NEEDS a better thermal path because it is creating more heat than the cree does. 
Someone complained about overdriving the cree. OK lets don't. cree 1000mA=275(per quoted specs of welight) K2 1500mA= 275. Thats a lot more energy going out of the battery to make what? light? no HEAT. Then if we do "overdrive" the cree than Holy Lumens Batman! I think Cree is very conservative on their speced drive levels. Remember they didn't spec a 1000mA drive level at one time. Did this mean the Cree XREs they made up to that point could not cope with 1000mAs? No. They could as the new spec was retroactive.

I don't(to a reasonable degree) care about lumens per dollar. I can see manufacturers caring but what do WE care? With the amount of money people here(myself included) pour into their flashlights what is a few dollars difference between these LEDs?

I don't care about a "Wide lambertian beam pattern" if it cannot deliver the goods. Crees are known for their throw. I have yet to see the cree handicapped because some of that light doesn't hit the reflector. Its not like the light that misses the reflector vanishes into the ether. It goes into the spill. And we like spill. Right?

Yes the K2 does not have rings. Yes I wish the cree did not have them. However it only matters if you are a white wall hunter. Not in real life.

I really want to like the K2 but I won't care until they can get closer to cree. Evan bear in mind that my frustration is really toward Lumileds.

Hows that for a knee jerk? 
By the way what does :tinfoil: mean?


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## evan9162 (Nov 16, 2007)

saabluster said:


> I don't(to a reasonable degree) care about lumens per dollar. I can see manufacturers caring but what do WE care? With the amount of money people here(myself included) pour into their flashlights what is a few dollars difference between these LEDs?



Your narrow view of peoples needs is both inaccurate and unhelpful. Many people consider price when evaluating LEDs for an application. What if you're using 10? 20? 50? A $5 difference per unit starts to add up pretty quickly. And when you pay a premium for top bins, the difference is more like $10 per unit. Not everyone thrashes their disposable income on premium parts.




> I don't care about a "Wide lambertian beam pattern" if it cannot deliver the goods. Crees are known for their throw. I have yet to see the cree handicapped because some of that light doesn't hit the reflector. Its not like the light that misses the reflector vanishes into the ether. It goes into the spill. And we like spill. Right?



Again, your narrow view of peoples' requirements makes your aguments and viewpoint laughable at best. There are more requirements than "OMG LUMENS!". You need to look past your own narrow viewpoints on how things are and consider that there are more diverse requirements than your cute little flashlight collection.



> Yes the K2 does not have rings. Yes I wish the cree did not have them. However it only matters if you are a white wall hunter. Not in real life.



Yes, the Cree is more efficient. Yes I wish the K2 was more efficient. However, it only matters if you're an efficiency freak. Not in real life.

See? Easy to turn things around. Narrow viewpoints don't help anyone.




> Hows that for a knee jerk?



At least you're still consistent.


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## saabluster (Nov 16, 2007)

I SO wish I could change my screen name to "OMG LUMENS!". That is brilliant.:twothumbs Thanks Evan!


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## Frobe22 (Nov 16, 2007)

Data sheet sometimes have to be interpreted. The printed numbers may be the same, but the conditions may be different.
Lumileds may be both conservative and slow, but they have a reputation for supplying reliable products. Who else have dared to quote a lifetime of 500 hours instead of 100 000 hours as some competitors?
There are a lot of people who don't recognize how important temperature is to white led brightness and lifetime.


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## evan9162 (Nov 16, 2007)

BTW...



> I don't care about a "Wide lambertian beam pattern" if it cannot deliver the goods. Crees are known for their throw. I have yet to see the cree handicapped because some of that light doesn't hit the reflector.



That's because no one has shown just how badly the beam profile of the Cree interacts with many reflectors.



> Its not like the light that misses the reflector vanishes into the ether. It goes into the spill. And we like spill. Right?



Unless you're looking at something 5' away, the spill is useless, and yes, the light does essentially vanish into the ether. All those extra lumens going out and missing the reflector are useless. In fact, they probably make things worse by illuminating the foreground objects moreso than needed, making it more difficult to focus on a distant object that's more dimly lit. The extreme case is when using a light to try to look at something through fog. In that case, any spill light is an extreme detriment.


Let's compare the beam profile of a Q4 XR-E to the -160 K2 (actual brightness, not relative):







Notice that from 0 to 50 degrees off axis, the XR-E is brighter, but after that, the K2 is brighter.

Now lets look at what a Mag reflector (used by many here) looks like:






So the Mag reflector doesn't capture any light before 47 degrees off axis. So all of the brightness advantage of the XR-E is lost when using a mag reflector.

Lets look at the lumen output vs. angle slice for each:


```
Angle	Q4 XR-E	-160 K2
0	0	0
5	0.6	0.3
10	4.1	1.9
15	5.6	2.7
20	7.3	3.7
25	8.6	4.7
30	9.5	5.6
35	10.0	6.3
40	9.9	6.6
45	9.1	6.7
50	7.4	6.6
55	5.4	6.3
60	3.5	5.9
65	2.4	5.5
70	2.3	4.9
75	2.2	4.0
80	1.7	2.7
85	1.5	1.3
90	1.4	0.4
95	0.6	0.0
```

Okay, so the Mag reflector doesn't catch anything between 0 and 47 - we'll just make it 45 for simplicity. So we throw out those values (since they mean nothing for throw), and we get this:


```
Angle	Q4 XR-E	-160 K2
45	9.1	6.7
50	7.4	6.6
55	5.4	6.3
60	3.5	5.9
65	2.4	5.5
70	2.3	4.9
75	2.2	4.0
80	1.7	2.7
85	1.5	1.3
90	1.4	0.4
95	0.6	0.0
------------------------		
Total	37.4	44.3
```

Oh. Look at that. The K2 actually puts more lumens into a Mag reflector than the XR-E does, even though it's total output is 20% lower.

So does beam profile still not matter? Sure looks like it makes a big difference to me.


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## Gomer (Nov 16, 2007)

It seems to me like these LEDs are nice for home lighting situations where you don't want to use a "massive" heatsink


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## saabluster (Nov 16, 2007)

evan9162 said:


> BTW...
> 
> 
> 
> That's because no one has shown just how badly the beam profile of the Cree interacts with many reflectors.



Well thats depressing. Now that you've shown us the "light" I guess all of our cree lights are going to be dimmer and have less throw.



evan9162 said:


> Unless you're looking at something 5' away, the spill is useless, and yes, the light does essentially vanish into the ether. All those extra lumens going out and missing the reflector are useless. In fact, they probably make things worse by illuminating the foreground objects moreso than needed, making it more difficult to focus on a distant object that's more dimly lit. The extreme case is when using a light to try to look at something through fog. In that case, any spill light is an extreme detriment.


Using your logic we should all be walking around with lasers. I'd like to see a show of hands of anyone else who agrees spill doesn't matter. This would make a good poll.

But if the only thing you care about is throw then your comparison of these two leds becomes pathetic. The reflectors collimate best at the outer edges because the die is more of a point source there. So even using this mag reflector which is not optimized for a cree we see it putting more light where it counts. Now if you want to compare apples to apples give the cree a reflector thats not patheticly shallow like the mag's. It will blow the K2 out of the water. This may change in the future when lumileds comes out with a better K2 but all I care about is now.


evan9162 said:


> Let's compare the beam profile of a Q4 XR-E to the -160 K2 (actual brightness, not relative):
> 
> 
> 
> ...





evan9162 said:


> So does beam profile still not matter? Sure looks like it makes a big difference to me.


No, not in this instance. Location, location, location! The cree has the light in the right spot.


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## Frobe22 (Nov 16, 2007)

Don't feed the trolls, they will never see the light...


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## evan9162 (Nov 16, 2007)

Yeah, definitely trolling. He's not even trying to have an intelligent discussion.


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## saabluster (Nov 16, 2007)

evan9162 said:


> Yeah, definitely trolling. He's not even trying to have an intelligent discussion.



Wait let me get this straight. I'M the one trolling. 
I just expressed my opinion about lumileds subpar product. And YOU came after ME. I was not directing attacks at you. It was toward the product as I mentioned. But YOU keep coming after me. Get off your high horse Evan Almighty. You certainly are no Newbie. You can argue with yourself from now on.-OMG Lumens


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## evan9162 (Nov 17, 2007)

And now you're resorting to personal attacks. Figures.


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## TorchBoy (Nov 17, 2007)

Well, I _was_ finding this quite interesting until it deteriorated at the end there.

I have to say that I do find a bit of spill quite handy. At the end of last week I even made my first caving headlamp using a Cree and reflector and I was quite excited about having the chance to test it today in a real cave. Sadly our caving trip has been postponed. :sigh:

I think the more LED types the merrier - something for everyone - but if you want throw why even bother with a reflector when so little of the LED's output will be hitting it, even if it _is_ a wide-beamed K2?


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## Kiessling (Nov 17, 2007)

As Mr. TorchBoy said ... interesting thread until the fighting broke out.

Gentlemen, please stop it and let the thread continue to be a worthy resource. Thanx 

bernie


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## koala (Nov 17, 2007)

evan9162 - thank you for your continuous update on the latest LED product. Your input is certainly an important asset to the LED flashlight community. Without your contributions there's probably a lot of misleaded sheep heading nowhere. Please don't let the others hinder your path. They are just obstacles waiting for the road roller to flatten them.


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## Anglepoise (Nov 17, 2007)

Thanks evan for the side by side comparison shots. Your work is much appreciated by many of us here so keep up the good work.

I think we will see lots of 'negatives' thrown at the new K2 due to so many people having modifying their lights to work well with Cree and Seoul products.
The thought of having to re tool their reflectors back to Lux III specs is rather daunting. Overall beam quality is important to me and due to this, I prefer the beam produced by a Lux III over Cree or Seoul. So I am hoping the K2 works out.


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## OMG Lumens (Nov 17, 2007)

evan9162 said:


> Lets look at the lumen output vs. angle slice for each:
> 
> 
> ```
> ...



I really wanted to point out that you should also include the bits of the beam between 0 and 10 degrees since they go in the direction you want without needing to use the reflector at all. Looking at the shape of that graph, I'd suggest if you included this it would more than compensate for what you lose at the edges, so the Cree would throw just as well as the K2, with the bonus of better spill for free. Unfortunately I've no idea where you get your figures from (which brings your whole calculation into disrepute), since they appear to bear no relation at all to what I can see in the graph, where the intensity is higher for the Cree up to 45 degrees, which isn't what is shown in that table!


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## SemiMan (Nov 17, 2007)

Actually the lumens from 0-10 degrees is pretty small for botht he K2 and the Cree...and this is the lowest bin K2 so not even that fair of a comparison.

Remember, this is not saying the K2 is better for everything, just better in a typical reflector. Yes you can make a deep narrow reflector that suits a Cree better.

Semiman



OMG Lumens said:


> I really wanted to point out that you should also include the bits of the beam between 0 and 10 degrees since they go in the direction you want without needing to use the reflector at all. Looking at the shape of that graph, I'd suggest if you included this it would more than compensate for what you lose at the edges, so the Cree would throw just as well as the K2, with the bonus of better spill for free. Unfortunately I've no idea where you get your figures from (which brings your whole calculation into disrepute), since they appear to bear no relation at all to what I can see in the graph, where the intensity is higher for the Cree up to 45 degrees, which isn't what is shown in that table!


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## TorchBoy (Nov 17, 2007)

Hmmm... Open spreadsheet... copy, paste... What *is* going on here? The area of the angle slice increases greatly as the angle increases? That's a big difference, all right.







evan9162 said:


> Let's compare the beam profile of a Q4 XR-E to the -160 K2 (actual brightness, not relative):
> 
> 
> 
> ...


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## evan9162 (Nov 18, 2007)

OMG Lumens said:


> I really wanted to point out that you should also include the bits of the beam between 0 and 10 degrees since they go in the direction you want without needing to use the reflector at all. Looking at the shape of that graph, I'd suggest if you included this it would more than compensate for what you lose at the edges, so the Cree would throw just as well as the K2, with the bonus of better spill for free. Unfortunately I've no idea where you get your figures from (which brings your whole calculation into disrepute), since they appear to bear no relation at all to what I can see in the graph, where the intensity is higher for the Cree up to 45 degrees, which isn't what is shown in that table!



Since the focused beam angle is less than 5 degrees, only the central 5 degrees matter in terms of what goes into the focused spot. So we'll add a stunning 0.6 lumens to the XR-E and 0.3 lumens to the K2. 

I'm using spherical geometry and the definition of lux to calculate lumens in a spherical ring

BTW, double registering is frowned upon here. You have been reported.


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## evan9162 (Nov 18, 2007)

TorchBoy said:


> Hmmm... Open spreadsheet... copy, paste... What *is* going on here? The area of the angle slice increases greatly as the angle increases? That's a big difference, all right.



Shperical rings are not equal in area. The area between 0 and 5 degrees is not equal to the area between 85 and 90 degrees. The area of a spherical ring increases as the angle offset increases.

A spherical ring between angle X and Y is equal to the area of a spherical cap of angle X minus the area of a spherical cap of angle Y. 

Here's how you calculate the area of a spherical cap (this does not tell you how to calculate it based on offset angle, but that's easy to derive with simple geometry)


http://mathworld.wolfram.com/SphericalCap.html
http://mathforum.org/dr.math/faq/formulas/faq.sphere.html


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## evan9162 (Nov 18, 2007)

Here are the areas of spherical rings, for a sphere 1m in diameter:


```
Angle range	area in m^2
--------------------------------
0-5		0.024
5-10		0.072
10-15		0.119
15-20		0.165
20-25		0.210
25-30		0.253
30-35		0.295
35-40		0.334
40-45		0.370
45-50		0.404
50-55		0.435
55-60		0.462
60-65		0.486
65-70		0.506
70-75		0.523
75-80		0.535
80-85		0.543
85-90		0.548
---------------------------
Total		6.283
```

Those ranges cover 1/2 of a sphere of a radius of 1m. The surface area of 1/2 a sphere with that radius is 2*pi, which is 6.283, so the math checks out.

Now, since the definition of lux is lumens per square meter:

lux = lm/m^2

Solving for lumens gives us:

lm = lux * m^2

We have m^2 for each angle range, now we just need to know lux for that range. So you set your LED under test 1 meter away from your light meter, and rotate it, measuring the intensity in lux for each offset angle. 

At this point, you now have how many lumens per offset angle (giving the data I posted earlier), and if you sum them all up, you get the total luminous output for the LED.


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## saabluster (Nov 18, 2007)

evan9162 said:


> BTW, double registering is frowned upon here. You have been reported.


Nice try but thats not me. Hence why I changed my sig slightly. I'm thinking its probably you.


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## evan9162 (Nov 18, 2007)

Not sure how you came to that conclusion...


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## Kiessling (Nov 18, 2007)

Please guys !!! 
This is the last warning for this thread. Stop the fighting, it leads no where.
bernie


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## TorchBoy (Nov 18, 2007)

evan9162 said:


> Shperical rings are not equal in area. The area between 0 and 5 degrees is not equal to the area between 85 and 90 degrees. The area of a spherical ring increases as the angle offset increases.



Yeah, I realised that just after I posted.  You'd never guess I used to be good at geometry. I decided to make a spreadsheet at the time, too, to see if I actually did understand it, and it looks like I got the same figures you did. Yay.


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## LEDite (Nov 18, 2007)

evan9162;

Nice work on the angle outputs.

For anybody actually using Hi-Power LEDs @ high currents, the lower thermal resistance (5.5 - 69% of the XRE) will enable lower operating temps.

This will improve the operating efficiency by keeping the chips cooler.

Larry


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## chris_m (Nov 19, 2007)

LEDite said:


> For anybody actually using Hi-Power LEDs @ high currents, the lower thermal resistance (5.5 - 69% of the XRE) will enable lower operating temps.
> 
> This will improve the operating efficiency by keeping the chips cooler.


Let's get that in perspective. We're talking 5.5K/W vs 8K/W, so at 1000mA that's ~9K difference in the junction temperature. Looking at how the junction temperature affects the efficiency, you lose a little over 2% for that temperature rise, or ~5 lumens. ISTM this is pretty negligible compared to normal differences in efficiency, and not something you should even consider in your purchasing decision (is about 1/3 of a bin for the Cree, so for their release schedule about 1 month of progress - maybe rather longer for Lumileds!)


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## evan9162 (Nov 19, 2007)

That's a pretty good point. We've reached the point of diminishing returns that improved thermal resistance nets us. Moving from 15C/W to 9C/W is much more beneficial than from 9C/W to 5C/W, considering that power levels have remained about the same. The improved thermal resistance will only be very benficial if LED manufacturers start dramatically increasing the current/power levels of the devices.


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## SemiMan (Nov 19, 2007)

evan9162 said:


> That's a pretty good point. We've reached the point of diminishing returns that improved thermal resistance nets us. Moving from 15C/W to 9C/W is much more beneficial than from 9C/W to 5C/W, considering that power levels have remained about the same. The improved thermal resistance will only be very benficial if LED manufacturers start dramatically increasing the current/power levels of the devices.



That is true for light output, but 10C could be the difference between a light that lasts as long as intended and one that does not. I think more important is you have lumen maintenance at a high temperature. The K2 is 120C at 1A drive. I was hoping for higher temperature, but that is still pretty high

Semiman


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## evan9162 (Nov 19, 2007)

Yep - for normal circumstances, the improved thermal resistance doesn't make too much of a difference.

However, if you are in a high temperature situation, the improved thermal resistance can mean the difference between meeting your design specification, or exceeding it. 

In reality, we all want the thermal resistance to be as low as possible.


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## mofiki (Nov 19, 2007)

Thankx evan9162 for your positive points about the K2. I just purchased 5 of the new K2's from Future because I felt they would compliment the application I intend to use them for. I oringinally built this light with the Cree Q4's and I must admit it didn't perfectly live up to my expectations, to much spot, I was hoping for more spill. I don't need the throw of a high power spot beam however I do want alot of light. I got a little worried after reading some of the comments in this thread that I might have made another mistake but because of the info you posted I think this may be the right choice. I guess alot of what I'm looking for might have something to do with choosing a lense or reflector too, I haven't had enough experience in those areas yet but something along the line of a 35W halogen medium bulb is what I'm hoping for. I may not use all five leds but I got extra just in case I make a mistake.


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## monkeyboy (Nov 20, 2007)

I just realised that the max junction temperature is only 150C like the Cree as opposed to 185C. Hmm... that's not so good. Are they just using the rebel die? In which case, why are there no 220 and 240 bins yet? I thought they would have been keen to use the latest technology in their newest product.


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## Opto-King (Nov 20, 2007)

I agree that the thermal resistance of 5degre C/W is very good, but I also noticed in the K2 (version 2.0) datasheets that the thermal resistance of LED when mounted on AlPCB Star is 9.5 degree C/W which is higher than both for SSC P4 and Cree when mounted on AlPCB Star, why is this?

Also, the CRI of the K2 is only 70 where as the SSC P4 and also Lexedis has up to 90 in CRI. And if I'm not misstaking when improved CRI the lumens out put can be dimmer but for the human eye the light output looks brighter. Any one that has a different idéa?


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## SemiMan (Nov 20, 2007)

monkeyboy said:


> I just realised that the max junction temperature is only 150C like the Cree as opposed to 185C. Hmm... that's not so good. Are they just using the rebel die? In which case, why are there no 220 and 240 bins yet? I thought they would have been keen to use the latest technology in their newest product.



The max die temperatures (where more instantaneous failures occur) are the same, but the lumen maintenance temps are different. Quoted from Cree Reliability Data Sheet "Based on this method, Cree projects XLamp LEDs to maintain an average of 70% lumen maintenance after 50,000 hours, provided the LED junction temperature is maintained at or below 80ºC." For the K2 is it 120C.

For flashlights, I doubt the difference is going to matter unless you use your flashlight 8 hours a day every day and plan to keep it for years. In other applications, it could make a big difference. Since Ambient + die temp rise + heat sink rise must be below that 80C or 120C, if you have a moderate to high ambient, there may not be much room left to dissipate in heat. If you know your ambient is going to be generally low, it does not matter as much. Keep in mind the released Crees have better efficiency, which may be able to offset the ability to maintain life at higher temps of the K2.


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## monkeyboy (Nov 20, 2007)

One application where temperature resistance is important is multi LED flashlights where the LEDs are being driven near the limit. e.g. the Wiseled tactical throttles down to avoid damaging the LEDs. LEDs with higher temperature resistance would be useful in these situations but I agree that Lumileds need to release more efficient LEDs for this to be an advantage over the Cree.


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## chris_m (Nov 21, 2007)

monkeyboy said:


> Lumileds need to release more efficient LEDs for this to be an advantage over the Cree.


Indeed - if hitting the limit is an issue, then simply drive the Cree at 125/135 of the current you're driving the K2 at to keep the temperature lower than the K2. You're losing <8% of te output this way, which is only 1 Cree bin (or 3 months Cree development time).

I'd suggest that for those here lumen maintenance is a non issue too - even the biggest user will only lose a tiny amount of lumens with flashlight use before advancing technology makes the LED in the flashlight completely obsolete.


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## saabluster (Nov 22, 2007)

chris_m said:


> I'd suggest that for those here lumen maintenance is a non issue too - even the biggest user will only lose a tiny amount of lumens with flashlight use before advancing technology makes the LED in the flashlight completely obsolete.


I agree completely.


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## Frobe22 (Nov 22, 2007)

This tread is listed under "Beyond Flashlight - LED", and still some of you are only concerned about flashlight use of these LEDs? How many times do we need to be told that lumen maintenance is't important for flashlights?


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## saabluster (Nov 22, 2007)

Frobe22 said:


> This tread is listed under "Beyond Flashlight - LED", and still some of you are only concerned about flashlight use of these LEDs? How many times do we need to be told that lumen maintenance is't important for flashlights?


So while talking about LED technology and what not we're not allowed to mention how it might apply to our first love? I can see not posting about your flashlights in custom forge or really any of the others under the "beyond flashlights" banner. But I think this(LED) is the exception. How are we supposed to talk about the pros and cons of new LEDs without bringing up how it would be in different applications? I get what your saying though and I suppose there is a fine line in this area.


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## chris_m (Nov 22, 2007)

Frobe22 said:


> This tread is listed under "Beyond Flashlight - LED", and still some of you are only concerned about flashlight use of these LEDs? How many times do we need to be told that lumen maintenance is't important for flashlights?


"Flashlight" was simply a generic term - I could just as well have said "bike light", "headlamp" or "homemade light", or even I'd suggest "household illumination" and the point would still stand. In any case my understanding of this forum is that it is for discussing LED technology away from the discussion of different brands of flashlights - doesn't mean that the application of that technology isn't still largely in flashlights for most people here. As one of the people advocating forming this forum, the point of it is simply that you don't have to scroll through loads of posts discussing the flashlights themselves.

FWIW I don't actually own a single flashlight with an LED in (yet) - my main applications are actually bike lights and headlamps.


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## Gomer (Nov 22, 2007)

> FWIW I don't actually own a single flashlight with an LED in (yet) - my main applications are actually bike lights and headlamps.



The only LED flashlight I own is one of those super cheap 3mm LED ones that was given to me for who knows why. My interest in these forums is actually aquarium (reef/planted tank) lighting.


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## saabluster (Nov 23, 2007)

Gomer said:


> The only LED flashlight I own is one of those super cheap 3mm LED ones that was given to me for who knows why. My interest in these forums is actually aquarium (reef/planted tank) lighting.


 
Good! There is still hope for you yet. Don't EVER buy one of the new led flashlights. There is no patch to wear to help you break the habit. Once you've started you can't stop.


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## Gomer (Nov 23, 2007)

well, I am still figuring out logistics on a "pendant" light...I guess that is like one of your big multi-LED lights 

I am just trying to make it psuedo economical and Q4/5 prices aren't dropping LOL. that coupled with only 1 source for the blue XR-E's makes it limiting (I know there are more, but there is only 1 that has prices posted). When you are putting something together with ..oh..12-14 LEDs to be run for 12hrs a day, you want it to be done right the first time.


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## adnj (May 20, 2008)

This is an old thread but I was reviewing it for the possibility of headlamp and interior light for automotive. Survivability at +10 years, snap in assembly with zero heatsinking to save weight. ambient temperatures of +140 deg F and surface mountable for manufacturability. If I were to look at those as priorities, I think that this is a candidate for headlamps. Yes?


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## saabluster (May 21, 2008)

adnj said:


> with zero heatsinking to save weight.


Not going to happen my friend. Not for ten years. You would be lucky to get ten minutes with the amount of power that would be needed for proper headlights.


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