# 100 Lumen Rebel technical evaluation



## evan9162

Good morning.

I received my 100 lumen Rebels yesterday, having only ordered them on Tuesday. That was with standard ground shipping even.

The bin I received is NVND. The new binning scheme for Rebels puts these parts as such:

N = 100-120 lumens
VN = Up and to the right of the W0 color bin (see binning chart)
D = 3.03-3.27V Vf

These binning values are at If=350mA.

Not bad - color probably could have been better, but that color bin probably also lends it self to a slightly warmer and more natural color output vs. something very cold, like a Y0 or XP binned emitter would. 

The lumileds description for the new high output rebels mentions new manufacturing techniques - new thin film technology that eliminates the sapphire substrate, and roughening of the emission surface to improve extraction efficiency. Given the mention of new manufacturing techniqes, we'd expect some visible differences between the new rebel and the old, and indeed, there are.

Here is the old rebel on the left (50 lumen white) vs the new rebel on the right (100 lumen white)







The new rebel appears to be using a different phosphor mix and application technique. Whereas the entire surface of the package of the old rebel is covered in phosphor, only the die and metal circuit strips of the new rebel are coated in phosphor. I verified this by shining a blue LED at both. The entirety of the old rebel fluoresces, while only the die and electrical traces on the new rebel fluoresce.

In addition, the die structure of the new rebel is clearly visible through the phosphor, compared to the old rebel. This indicates a new phosphor mix. If the old phosphor mix were applied this thinly, the output color would have a tremendous blue tint to it. 

The thinner phosphor and removal of the sapphire substrate in the construction of the die should also have an effect on the apparent height of the die as well. While difficult to see, this shot shows it best - the die of the new rebel is definitely shorter by a small amount:






This should affect the beam profile slightly, causing the beam of the new rebel to project more forward relative to the old rebel.

I attached the new rebel to my angular measurement rig, and created a beam profile. Here is the new rebel beam profile, compared to the old:






Indeed, the new rebel does project slightly more forward (slightly more narrow beam) than the old rebel does.


So the big question is: Do the new rebels perform as claimed? Indeed they do. I ran the new rebel through its paces at various currents, calculating the luminous output at each. 

Here is the raw data for the new rebel's performance:




Code:


Current (mA)	0.1	30	130	310	670	980	1260	1570	1930
--------------------------------------------------------------------------------------
Vf		2.55	2.72	2.96	3.11	3.26	3.34	3.39	3.44	3.51

Watts		n/a	0.08	0.38	0.96	2.18	3.27	4.27	5.40	6.77

Lux		n/a	n/a	11.6	25.0	45.8	59.7	70.6	79.2	85.6

Lumens		n/a	n/a	45	98	179	234	276	310	335

Lumens/W	n/a	n/a	118	101	82	71	65	57	49




Here is the new rebel, compared to its competition: The Seoul P4, Cree XR-E, Luxeon K2, The older Rebel, a Luxeon V, and even a lowly Luxeon III:

First, Vf:






The new rebel has the lowest Vf of all the competing products. You can see the difference between the new rebel, and the old Luxeon III - the new rebel stays much flatter, reducing power dissipation at high currents.

Because of its serial-parallel arrangement, the Lux V has a Vf twice that of all the other parts. I've omitted it from this graph since it would change the vertical axis, reducing the resolution for the remaining plots.


Next, output:






Not too long ago, W-bin Lux Vs were highly sought, and demanded a healthy premium (upwards of $40). Today, a $6 rebel bests a W-bin Lux V in terms of output at a given current (and beats it hands down in terms of efficiency). *The rebel easily breaks 300 lumens at 1.5A.* This is important. It means Lumileds can slap the same die/phosphor combination in a K2 right now (which is rated for 1.5A), and market a 300 lumen, single-die LED.

Output really drops off at the near-2A mark. With output of less than 350 lumens, this tells us that there's still a ways to go before we hit the 500 lumens at 2A mark that Lumileds has promised. We'll have to wait and see how long it is until that part is released from Lumileds. After what happened with the K2, there are still many who are (rightfully) gun-shy about Lumiled's announcements. Hopefully this new rebel isn't the Q3 product release that Lumileds has alluded to in their press release about the 500-lumen parts.


Finally, here's a unique way to look at efficiency: "Droopyness". I'm including this, because one of the big announcements from the early year press releases was that of Lumileds claim of fixing "droop", which is a dropoff in efficiency (lumens/W) at high currents.

If the new rebel has this anti-droop technology, then we should see its efficiency stay relatively higher at high currents compared to other devices.

The droop factor for a given current is the efficiency at a test current, divided by the efficiency at 130mA, or:

Df = E(test)/E(130mA).

So if the new rebel does indeed have anti-droop technology, then its efficiency at high current shouldn't drop as much from the efficiency at 130mA, compared to other products. Let's find out:






In fact, the new rebel suffers from "droop" the exact same amount as other products in its class. The K2, Seoul, and Cree all exhibit the same level of "droop" as the new rebel. While the old rebel appears to droop more, this is due to less-than ideal heatsinking for the old testing, as the droop graph for the old rebel matches all the others until high current (1A and greater).

So we can conclude that either A) the new rebel does not have the "anti-droop" technology, or B) such claims are bunk. Who knows? We won't really know until Lumileds directly claims that a product does contains such technology, and we can test it ourselves.

So, there we have the technical bits. As far as a conclusion? 

Well, is it worth swapping out your Seoul or Cree parts for a new rebel? Probably not.

Is it worth using a rebel instead of a Seoul or Cree part for a new build/mod? That really depends on you - the rebel can be a real PITA to deal with, not only because it has a different mounting method than we're used to (power and thermal pads are on the bottom), but also because the thing is so damn small! So the decision to use the rebel depends on if you're willing to work through the unique mounting requirements, and the possibilty of losing a $6 LED if you happen to sneeze 

However, it does finally make the rebel line a more compelling part to use, now that it directly competes with the brightest power LEDs. The diminutive size is either a curse or a blessing, depending on what you're trying to do. If you're trying to cram a high brightness part into a tiny space, you now have another option.

Just like with my last evaluation of rebel parts, I'm likely to not use these very much. However, I hope this means that Lumileds will soon bring the K2 line up to the performance level of the new rebel.


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## McGizmo

Well done and clear comparative work! Thanks!! :thumbsup:


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## kiely23+

thanks evan... :twothumbs


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## LukeA

You can solder to the top of the Rebel, you just have to remove some silicone with a pin.


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## OhMyGosh

evan9162: Thanks a lot for all the info! WOW!

It is very interesting to see that the lumen/watt for different drive levels is similar to current LED's. Really amazing you did all this in one day.

Did you get these from Future? I have 10 of them but can't find any info on what bin they are. I am still busy destroying cool40's learning to solder them. - oops just saw the NVND is on the invoice but not the package.

LukeA: that tip is just what I needed! thanks


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## IsaacHayes

Great work! Was the Cree you used in your test the old 3 bond wire or the new 4 bond wire ones?

Makes me want to get one to experiment with. Heh.


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## McGizmo

I would like to add some preliminary optic observations in regards to the Rebel. Although the package itself is quite small, the image size and location is such that it is more comperable to the larger LED's than one might initially expect. To bring the Rebel into focal allignment with most of the reflectors we are familiar with, one needs to bring the whole LED into the reflector; package included. This means that in many cases the heat sink itself also needs to come inside the parabolic chamber.

Now one can design a reflector with a very short focal length and small enough that it seats down on the package and comes close to the dome of the LED. I designed one such reflector that has a 10 mm OD and fits down as one would expect a reflector to mate to this LED. I have production pieces now and they work nicely with the 80 lumen samples I received a while ago (I was slated for some of these 100 lumen parts but a rep brainfart and or loss in the mail have left me still in waiting). So, neat little reflector and neat little package. 

*BUT*. 

The beam distribution I see from the Rebel coupled with this McR-10R reflector is very much akin to the KL4 with its 5W LED and 20 mm reflector. Spot and spill angles are very similar as is the transition from spot to spill in terms of intensity. I said BUT because I believe many expect that the tiny Rebel will lend itself to a tiny "throw monster". I do believe that one can make a tiny light that competes with the KL4 in terms of flux and lux and for those who appreciate the KL4 there is clean potential for shrinking the overall package.

If you want to come up with a light that is on par in terms of beam angle and level of divergence comperable to the Seoul P4, Luxeon or XR-E with the Rebel, you will be working with the same sized optics.

The Seoul 1/2 watt with its tiny die is the candidate for a tiny "throw monster".

I am no expert by any means and what I have said is based on a limited understanding and some empirical investigation.


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## jtr1962

Even though it appears that the Rebel doesn't use anti-droop technology, the efficiency of 71 lm/W near the maximum rated current is very impressive. This basically means you can use these for home interior lighting, and even including driver losses of 10% of so they will still be better than most CFLs when giving the maximum amount of light per LED. No need to underdrive them at all in the name of efficiency, although if you do you could approach T8 linear tube efficiency. 234 lumens is enough to more than replace a 25 watt small base incandescent (those are horribly inefficient) while using maybe 1/7 of the power.

I can't wait to get my hands on a few of these so I can run my own testing.


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## evan9162

IsaacHayes said:


> Great work! Was the Cree you used in your test the old 3 bond wire or the new 4 bond wire ones?
> 
> Makes me want to get one to experiment with. Heh.



The 3 bond wire version. My XR-E isn't the cream of the crop, just a P4 bin.


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## filibuster

No wonder Cree has been marching up the flux bin chart so quickly lately with new bins coming out before they are even announced as available.


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## Gryloc

Evan, 

Thank you for the thorough review of the newer Rebels! It is nice seeing some real data every now and then! It is also great seeing a dedicated truth-seeker. Your review was so detailed and it shows how technology is really moving along. 

I was wondering about a few things first. Even though it is a PITA to solder, but once you have just that one heat-sinking thermal pad soldered to a chunk of copper (or whatever), did you find the thermal transfer to be adequate when driving it up to specs (700mA)? Is there a way to find how hot the emitter gets, or does it get too hot to touch? I was trying to think of ways to increase thermal transfer, like having a little thermal epoxy between the thermal pad and the two +/- pads. How did you set it up? 

Do you think that one could file off the thermal pad and two contacts (for a perfectly flat surface) and just use a super-thin layer of thermal epoxy? You would then connect your power wires to the top of the LED where the traces are. With the pads still in place, and with the use of epoxy, I figured that the surface would be too rough and there would be too many medians for the heat to travel through (heat -> ceramic substrate, to adhesives for the traces, to copper pad trace, then to epoxy, and so on). It sounds stupid, but it may allow more beginner modders to embrace this Rebel. I suppose this technique is like how you would epoxy a Cree XR-E. I was just wondering -hoping that there may be an improved method of mounting these. If only they made that copper thermal pad a little bigger.

I noticed that you have a decent testing rig, but how do you measure lumen output? Do you have access to an integrating sphere, or did you make your own? I was always wondering about that.

How did the Rebel like the 1000mA to 1500mA, or even the 2000mA? Did things still stay cool at these levels? Were you at all concerned about heat at any specific current? I know that the LED die can handle the current (you proved it -and LED dies are tough), but I was hoping that the package could handle the transfer heat. Did the tint shift any? If so, at which current level? I was hoping that the new phosphors used would hold up to intensity-degrading heat. Do you think that the Rebel uses a phosphor similar to what Seoul uses on their P4?

Finally, is it possible if I can use your data to compare it to other LEDs? I am making a spreadsheet that compares data with what other testers found, as well as the original datasheets. There will be several graphs comparing luminous flux, intensity at the different currents, efficiency (lm/W), and forward voltage. I would like it to be very complete, while being as accurate as possible. With this preadsheet, sometimes you are able to see variations in the heatsinks used, bins of LEDs, etc. It would be very useful. When I finish, I plan to post the spreadsheet on CPF for all to use. That would be very nice of you. I am still waiting on jtr1962 to post his results of the Rebel 0100's that he is getting.

Thank you. There is still many things to learn about these new beasts. I need to order a few for myself to try out. I wish I had a light meter and better equipment to show my own results. I would like to use them up to 1500mA (or more depending how they performed). It would be very nice to use the awesome efficiencies of this thing at over 1A (70lm/W at 1A down to 45lm/W at 2A). It looks as though I may have to mod my quad M*g again and up the current more.... :duck:


-Tony


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## Gryloc

McGizmo,

Sorry this is not the correct thread, but can you give some more information about this Rebel reflector in your "McGizmo" zone of CPF? I had some questions about it and how it compared to your old McR8. It sounds great. Finally an optic/reflector that takes advantage of the Rebel's small size! I also had some technical questions about the reflector for the Rebel. Thank you.

-Tony


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## evan9162

> I was wondering about a few things first. Even though it is a PITA to solder, but once you have just that one heat-sinking thermal pad soldered to a chunk of copper (or whatever), did you find the thermal transfer to be adequate when driving it up to specs (700mA)? Is there a way to find how hot the emitter gets, or does it get too hot to touch? I was trying to think of ways to increase thermal transfer, like having a little thermal epoxy between the thermal pad and the two +/- pads. How did you set it up?



Here's how I mounted the rebel to my testing heat sink:






I used some thermal epoxy and epoxied the rebel, hanging halfway off a strip of 1/16" aluminum. I made sure there was a minium of thermal epoxy on the rebel, then pushed down hard on the corners of the rebel to ensure as thin as possible of a layer. I also ground a couple of round notches for the screws. Finally, I hand soldered the wires to the underside of the rebel. If I were to use the rebel in a real application, I think I would consider this method first.

On my previous rebel testing with the 50 lumen part, I was concerned about damaging the part, and didn't press down as hard. This left a much thicker layer of epoxy between the rebel and aluminium. As you can see from the output dropoff, and "droop" graph, this had a pretty big impact on the high current scaling. So keeping as thin of a layer of epoxy as possible is a must for the rebel, due to the miniscule contact area. You can get away with a thicker layer of epoxy on other parts, like the Seoul, K2, and Cree, because the contact area is so much larger (probably up to 10x as large).





> Do you think that one could file off the thermal pad and two contacts (for a perfectly flat surface) and just use a super-thin layer of thermal epoxy? You would then connect your power wires to the top of the LED where the traces are. With the pads still in place, and with the use of epoxy, I figured that the surface would be too rough and there would be too many medians for the heat to travel through (heat -> ceramic substrate, to adhesives for the traces, to copper pad trace, then to epoxy, and so on). It sounds stupid, but it may allow more beginner modders to embrace this Rebel. I suppose this technique is like how you would epoxy a Cree XR-E. I was just wondering -hoping that there may be an improved method of mounting these. If only they made that copper thermal pad a little bigger.



I think the key with the rebel is to keep it as simple as possible - these parts are small...damn small. I can't imagine trying to grind or cut anything on the parts, so my plan is to leave them as-is, with no modifications. So for me, the hanging-over-the-edge mounting technique is what I plan to persue.




> I noticed that you have a decent testing rig, but how do you measure lumen output? Do you have access to an integrating sphere, or did you make your own? I was always wondering about that.



I'm using a lumen integration technique, where I use an angular measurement rig to rotate the part under test relative to the light meter. This is how I generate a beam profile of the bare part. I then use some geometry to find out the area of a set of concentric spherical caps at the measured angles, given the area of a partial sphere of a given angle. I then use the definition of lux (1 lux = 1 lumen / square meter), and sum up all the parts. In essence, what I do is to create a "lumen factor", where I can measure a bare part on-axis, then multiply by a constant to get luminous output.

I used this method to measure the output in lumens of the CPF test lights from the light meter testing thread. We later sent those lights off to a test lab to be measured on a real, calibrated, integrating sphere. All of my calculations for lumens were within 5% of what the lab produced. So I'm quite confident in my measuring methodology.



> How did the Rebel like the 1000mA to 1500mA, or even the 2000mA? Did things still stay cool at these levels? Were you at all concerned about heat at any specific current? I know that the LED die can handle the current (you proved it -and LED dies are tough), but I was hoping that the package could handle the transfer heat. Did the tint shift any? If so, at which current level? I was hoping that the new phosphors used would hold up to intensity-degrading heat. Do you think that the Rebel uses a phosphor similar to what Seoul uses on their P4?



The rebel seemed to handle all of the current levels well, except for the 1970mA level. I think Lumileds rates the rebel at 1A because of package power dissipation constraints, rather than what the die can handle (since the thermal pad area is so darn small). Since the die is directly mounted to the package (no bond wires), you're definitely in no danger of fusing open bond wires - so you would have to do serious damage to the die in order to actually kill the LED.

You can tell if your LED is starting to seriously heat up in 2 ways:
1) Since the Vf of an LED drops when it heats up, then you can monitor the Vf after powering it up to a certian current level. If it drops rapidly, then the LED is heating up quite a lot, and you're probably driving it at a very high level compared to what it can handle thermally. By rapidly, I mean dropping 10mV every 2 or 3 seconds, and dropping 100mV in the first 10-20 seconds. If it only drops 10 or 20mV in the first minute, then you're probably doing okay.

2) The light output also drops with increasing temperature, so monitor brightness with a light meter. My guesstimate is that dropping 1% every 10 seconds right after powerup indiciates pretty high drive level, and higher temperatures.




> Finally, is it possible if I can use your data to compare it to other LEDs? I am making a spreadsheet that compares data with what other testers found, as well as the original datasheets. There will be several graphs comparing luminous flux, intensity at the different currents, efficiency (lm/W), and forward voltage. I would like it to be very complete, while being as accurate as possible. With this preadsheet, sometimes you are able to see variations in the heatsinks used, bins of LEDs, etc. It would be very useful. When I finish, I plan to post the spreadsheet on CPF for all to use. That would be very nice of you. I am still waiting on jtr1962 to post his results of the Rebel 0100's that he is getting.




Definitely, please do. I post this kind of information for the benefit of everyone on CPF.


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## Anglepoise

Thank you very much for the info you have given us. Much appreciated.


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## Gryloc

evan9162 said:


> The rebel seemed to handle all of the current levels well, except for the 1970mA level.




So, you were saying that over 1620mA, the Rebel wasn't very "happy". What was going on at that 1970mA level? Were you talking about heat? Anything else wrong? I wanted to know if I would be able to thermally attach the Rebel to a good heatsink well, could the LED handle the higher currents? I would love to hook this to a water-cooled heatsink and really crank up the amperage (2.5A? 3A?) until the efficiency drops to the 30lm/W that the old K2 would operate at. Would you be willing to do such a test as this? Sure the intensity levels off some, but why not go further? It seems as though heat is the only limit. That would be interesting.

I would have to work on "shaving" off those three bottom pads. Maybe an hobby knife would work. Filing would be tough, as would using a cutting wheel on a dremel (shooting Rebels lol). If you are using epoxy on a small amount of surface and it is doing well, then epoxy over the entire bottom surface may be a little better. The ceramic substrate is a good heatsink, so having as much of the surface potted to a heatsink as possible is key, otherwise it seems like a waste. It is like applying thermal epoxy to only the right half of a Luxeon emitter slug. Now I want to really try this out.

Did your power supply have fixed current levels? I was wondering why it had steps with odd current levels (odd to us high-power LED guys atleast). I knew there was a way to measure lumens with a light meter. Once I get mine (some day), I will check back with you on the exact process. Good job with your close readings compared to calibrated equipment.

When you measure the lumens, do you have to read the lux at 5 degree increments for the entire 90 degrees? Does that mean that you have to have the LED running almost constantly? Hopefully the Rebel doesn't get hot during that time. In that case, do you think that the lumen output could be just a little better at higher currents if the luminous flux reading was taken at one time? Well, now I think of it, this heat could be a good thing because you get more "real-life" results by having the LED on for longer to allow the temperature to stabilize. 

Finally, if you would like to see more of the Rebel in all its glory (the older 0050 part, atleast), then you may want to check out this link:

https://www.candlepowerforums.com/posts/2065408#post2065408

It is a couple weeks old, but I guess not too many were interested in it at the time. He showed some pretty good close-up pictures of the naked (although phosphor stripped) Rebel die. Maybe McGizmo can benefit from this. The die on every LED is so small (the 1in X 1in), but the Lambertian dome really magnifies the die. If the Rebel had a truly 180 degree dome, would it collaminate better with a reflector? Thanks again for all the information. Keep up the great work! I hope to see more results of this Rebel. 

-Tony


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## SemiMan

I think for good heat transfer it is essential to solder the rebel as opposed to epoxy. Solder is roughly 5-10 times more thermally conductive than thermally conductive epoxies. It is not easy to do by hand, but the heat plate method works and if it is a small piece, you can probably hand solder if you have a good iron and can heat the whole piece.

Semiman


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## evan9162

> So, you were saying that over 1620mA, the Rebel wasn't very "happy". What was going on at that 1970mA level? Were you talking about heat? Anything else wrong? I wanted to know if I would be able to thermally attach the Rebel to a good heatsink well, could the LED handle the higher currents? I would love to hook this to a water-cooled heatsink and really crank up the amperage (2.5A? 3A?) until the efficiency drops to the 30lm/W that the old K2 would operate at. Would you be willing to do such a test as this? Sure the intensity levels off some, but why not go further? It seems as though heat is the only limit. That would be interesting.



Heat was certianly the limiting factor, but there's probably not much that can be done about it. At 1970mA, there's 6.77W being dissipated. The junction->case thermal resistance is 10C/W, but given the tiny size of the contact area, and the multiple thermal interfaces (Pad->Al strip-> Heat sink), thermal resistance was probably higher (13C/W), pushing the junction temp up to at least 120C or higher. I measured the top of the package at 1970mA, and it hit over 50C. So things are getting pretty darn hot at that current level. It's pretty difficult to get great thermal transfer with such a small area - again why I think lumileds specs the rebel to 1A.




> I would have to work on "shaving" off those three bottom pads. Maybe an hobby knife would work. Filing would be tough, as would using a cutting wheel on a dremel (shooting Rebels lol). If you are using epoxy on a small amount of surface and it is doing well, then epoxy over the entire bottom surface may be a little better. The ceramic substrate is a good heatsink, so having as much of the surface potted to a heatsink as possible is key, otherwise it seems like a waste. It is like applying thermal epoxy to only the right half of a Luxeon emitter slug. Now I want to really try this out.



It would be interesting to try, but hard to determine how effective it is. I don't think the ceramic is very good at transferring heat linearly, which is probably why they didn't bother to make the thermal solder pad on the bottom much larger. The ceramic is only 0.5mm thick, so heat travelling from the die to the thermal pad only goes through 0.5mm of ceramic, but heat travelling to where the power pads are travels through 3-4mm of ceramic, 6-7 times the distance, making that part of the package much less effective at moving heat than the part right below the die.





> Did your power supply have fixed current levels? I was wondering why it had steps with odd current levels (odd to us high-power LED guys atleast). I knew there was a way to measure lumens with a light meter. Once I get mine (some day), I will check back with you on the exact process. Good job with your close readings compared to calibrated equipment.



Yes, I'm using an LM317 in constant current mode, with a set of currents I can additavely switch in and out. There are 5 switches , 30, 130, 310, 670, and 1260mA. I can turn on multiple switches and the sum of the two switches is the current that flows - i.e. turn on the 310 and 670 switch to get 980mA.




> When you measure the lumens, do you have to read the lux at 5 degree increments for the entire 90 degrees? Does that mean that you have to have the LED running almost constantly? Hopefully the Rebel doesn't get hot during that time. In that case, do you think that the lumen output could be just a little better at higher currents if the luminous flux reading was taken at one time? Well, now I think of it, this heat could be a good thing because you get more "real-life" results by having the LED on for longer to allow the temperature to stabilize.



When I'm doing the beam profile, I usually run at a lower current, like 310mA. At that current level, heating has little to no impact on the lux readings - they settle down in a few seconds after powerup and are stable, and I do a check at 0 degrees right at the end to double-check my readings to make sure heat hasn't caused the LED output to drop. Once I have the beam profile and I calculate the lumen factor for that kind of LED, I can apply that lumen factor across all measured current levels, and I can measure multiple LEDs of the same product type simply by measuring the brightness at 0-degrees.

I only need to measure the beam profile for one sample of a kind of LED. But I make sure to measure the beam profile on any parts that could have significant changes, such as the new rebel vs. the old. If/when Lumileds releases a K2 in this same output range, I will most certianly re-measure the beam profile since changes to the die and phosphor will definitely affect the beam profile.




> If the Rebel had a truly 180 degree dome, would it collaminate better with a reflector?



If the beam were even across 180 degrees, then we would get a higher percentage of the emitted light hitting the reflector and in the focused beam, but really, the beam profile of the rebel is targeted at being a Lambertian profile, which has certian characteristics.

I did some calculations once and found out that using standard reflectors, like the 50mm reflector in C and D cell Mag Lites, only 40% of the light emitted is in the focused part of the beam, and the remaining 60% is emitted out the front as spill light. The forward-emitting nature (without optics) of most power LEDs lends themselves more to using an optic rather than a reflector.

So working well with a reflector can mean a lot of things - it can mean that more of the light hits the reflector and ends up in the focused beam, it can also mean that the beam focusses down to a smaller spot, allowing more throw. Focusing to a smaller spot depends on how large the light source appears to the reflector - so smaller dies will focus better. The optics of the package also make a difference. The side-emitting luxeons throw most of their light in the 80-120 degree range, perfect for a reflector. So the vast majority of the lumens are going into the reflector and not out the front with side-emitters. However, the beam distribution is such that the side emitter appears as a larger light source with multiple nodes, so the beam can't be snapped into a tight focus like when using a high-dome (lambertian) emitter (like the rebel/k2/etc). So even though there are more lumens in the focused part of the beam, it may not be any brighter, just larger.

Optics are something that people have been trying to tame for some time now. It doesn't help that in the last couple years, the brightest LEDs are now coming from 3 different manufacturers, in 3 different packages, with 3 different kinds of beam patterns (K2, Seoul P4, Cree XR-E). It was hard enough when we had 5 years where the optics remained the same (just luxeons).


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## LukeA

SemiMan said:


> I think for good heat transfer it is essential to solder the rebel as opposed to epoxy. Solder is roughly 5-10 times more thermally conductive than thermally conductive epoxies. It is not easy to do by hand, but the heat plate method works and if it is a small piece, you can probably hand solder if you have a good iron and can heat the whole piece.
> 
> Semiman


I think sanding a corner of the Rebel so the heatsink solder pad is visible from the side, laying it into position, and wicking a little solder beneath it would work.

I would try this but I have no more (inexpensive) 50/95 Rebels to play around with.


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## jtr1962

evan9162 said:


> I don't think the ceramic is very good at transferring heat linearly, which is probably why they didn't bother to make the thermal solder pad on the bottom much larger.


Not necessarily true. The ceramic faces of a thermoelectric module are usually made of alumina ceramic. My guess is that the Rebel and the Cree both use this. It has a thermal conductivity of 35.3 W-m/K. Berylia ceramic can be 230 W-m/K. For comparison aluminum is 204 W-m/K. You're probably right though about them not making the pad larger because the ceramic, even with a high thermal conductivity, won't transmit heat linearly that well when it's so thin. They could have made the ceramic thicker, which would transfer heat linearly better, but then you'll have worse performance transferring heat directly under the LED die. There is a optimal thickness for which the total thermal impedance is at a minimum. My guess is that this is the thickness Lumileds used, and then based the thermal pad size on that.


----------



## pokkuhlag

Thanks for your testing the rebel, but I still have some questions about your test.

Since light meters are more sensitive to yellow-green, doesn't this affect your lumen measurements, by using different bins of leds, for example a WO bin vs VN bin?

About the thermal epoxy layer being extra thin for the Rebel, a thin epoxy layer is always better. Wouldn't this be unfair for the other leds with thicker layer of epoxy? Especially the Cree XRE since it uses a ceramic substrate as well?

The die of your rebel is off center, how would that effect the beam if you put it behind a reflector? This is would be interesting to see, since the die vs lens ratio is larger than other leds.


----------



## LukeA

pokkuhlag said:


> The die of your rebel is off center, how would that effect the beam if you put it behind a reflector? This is would be interesting to see, since the die vs lens ratio is larger than other leds.



It isn't off center; what you're seeing is an optical illusion caused by the dome.


----------



## SemiMan

*Rebel warning....*

Ok, that was just to get your attention.... more of a WOW than a warning.

I have 4 -100 lumen rebels on a metal core board. The Rebels are as close together as I could get them. They are soldered on.....pictures to follow.

I mounted the metal core board (about 2cm on a side square) on a heat sink then put 350 and then 700mA through it. First wow, at 350mA, the forward voltage was 11.85V for four in series. The LEDs had been on about 2 or 3 minutes.

I then ran them at 700mA and expected the heat sink to get much hotter than it did. I put my fingers on the metal core board and it was still not overly hot. I then put my fingers right over top of the domes of the four rebels and my finger pretty quickly got hot. Here is where my second WOW came in. I thought that my finger was heating up from thermal transfer from the dome however, I noticed that even when my finger was a few millimeters above the LEDs that my finger was still getting hot quickly. I then realized that the heating was from the visible light output of the LEDs ...second WOW. 

Semiman


----------



## johnny13oi

SemiMan said:


> I think for good heat transfer it is essential to solder the rebel as opposed to epoxy. Solder is roughly 5-10 times more thermally conductive than thermally conductive epoxies. It is not easy to do by hand, but the heat plate method works and if it is a small piece, you can probably hand solder if you have a good iron and can heat the whole piece.
> 
> Semiman



Would the heat from a soldering iron kill the emitter? I always that extreme temps would kill any LED emitter.


----------



## LukeA

johnny13oi said:


> Would the heat from a soldering iron kill the emitter? I always that extreme temps would kill any LED emitter.



I killed a 50/95 by getting it stuck to a blob of solder stuck to my 35W, 750˚F iron for about a second.


----------



## evan9162

> Since light meters are more sensitive to yellow-green, doesn't this affect your lumen measurements, by using different bins of leds, for example a WO bin vs VN bin?



not necessarily. Many light meters have different sensitivity curves. I don't really think that you will get much variation in the readings unless you're comparing extreme tints. I think you might have to start considering tint when looking at warm whites vs. cool whites, but for what I'm testing, I don't think it makes that much of a difference.



> About the thermal epoxy layer being extra thin for the Rebel, a thin epoxy layer is always better. Wouldn't this be unfair for the other leds with thicker layer of epoxy? Especially the Cree XRE since it uses a ceramic substrate as well?



I don't know what you mean by "unfair", but if you look at the brightness curves and "droop" graphs, you'll notice the only one that's out of sorts is the 50 lumen rebel, and that is due to known heatsinking problems. Since all of the other graphs are in-line with expected results, then the heatsinking for the other test LEDs is sufficient. The cree has a much larger contact patch, so ensuring a very thin epoxy layer isn't as critical. 



> The die of your rebel is off center, how would that effect the beam if you put it behind a reflector? This is would be interesting to see, since the die vs lens ratio is larger than other leds.



As Luke said, the die isn't off center, it appears that way since the rebel wasn't completely perpendicular to the camera.


----------



## Gryloc

It looks like if you are careful and quick with the soldering, things should be fine. I was soldering one of the Luxeon PWT emitters when I lost it. I could not find it on my desk anywhere. After a few seconds I discovered it stuck to the tip of my soldering iron. Surprisingly, that thing survived and is still working like nothing happened. It must have had poor thermal contact to one of the contacts. That is too bad about your Rebel, though. That will happen to many of us!

evan9162, even if the ceramic substrate only worked linearly, where heat seems to travel the shortest distance, then why does't the heat transfer pad sits all the way directly below the die? The majority of the thermal pad sits above further towards the top of the Rebel, so the pad only sits directly under what looks like 90% of the die. If heat does not like to travel those distances as well, then what where the designers thinking? That is why I wanted to know why the pad was not any bigger or moved down directly beneath the die. Why not take advantage of all that space between the heat pad and the contact pads? There is 1.8mm of room. I understand that there has to be enough space so the solder does not bleed over and bridge, but you would think there would be more problems of bridging between the two power contacts (only 0.4mm space). Just a thought. 

LukeA, do you mind if I show small snippets of your naked Rebel pictures (sounds naughty). I was going to show the pad placement compared to the die. I will post the snippet in this current post by editing it in later. Thanks.

Semiman, that is good news. A Vf of 11.85V / 4 = 2.96V each! Sure that is after it was running for a couple of minutes, but that is good. Wait till after a few hours of total use. Then the Vf will be even lower. Which Vf bin do you have? That is good the heat is escaping with the light, I suppose. It means less power dissipated in the heatsink. Keep us posted with your results. So far, between evan9162's data, and the little comments by Semiman and others, this Rebel is looking even more promising! Oh, I wish Newbie could be here and posting about his opinions and his results.

I have had some odd ideas brewing in my head about using these Rebels in some forward lighting in my car (strictly low beams), and because of that low Vf after the LEDs warmed up, I feel better about choices for driver circuitry, as well as my choices to cool them. A 13.5V-14.5V input (with engine running) and a LED Vf 13.34V (when using evan9162's data at 980mA) is certainly odd. Hopefully with lower Vf under 13V will make things easier. Yay.


-Tony


----------



## LukeA

Gryloc said:


> LukeA, do you mind if I show small snippets of your naked Rebel pictures (sounds naughty). I was going to show the pad placement compared to the die. I will post the snippet in this current post by editing it in later. Thanks.



Sure.


----------



## evan9162

Gryloc said:


> It looks like if you are careful and quick with the soldering, things should be fine.



Indeed, I hand soldered the power wires - limiting iron contact to a second or less is critical to this. Also, heeding the maximum temperatures shown in the reflow solder graph on page 9 will help to prevent heat damage from soldering.




> evan9162, even if the ceramic substrate only worked linearly, where heat seems to travel the shortest distance, then why does't the heat transfer pad sits all the way directly below the die? The majority of the thermal pad sits above further towards the top of the Rebel, so the pad only sits directly under what looks like 90% of the die. If heat does not like to travel those distances as well, then what where the designers thinking? That is why I wanted to know why the pad was not any bigger or moved down directly beneath the die. Why not take advantage of all that space between the heat pad and the contact pads? There is 1.8mm of room. I understand that there has to be enough space so the solder does not bleed over and bridge, but you would think there would be more problems of bridging between the two power contacts (only 0.4mm space). Just a thought.



I have a feeling this was to make space for more thermal vias around the thermal pad. If you look at page 11 of the rebel datasheet, you'll see the recommended PCB layout, with thermal vias. There are a number of vias between the thermal pad and power pads. It may be that they found that the vias being there were more important to thermal transfer than the thermal pad utilitzing that same space. I think a Lumileds engineer would have to be the one to answer that question.


----------



## Gryloc

Hmmm, as for why they did that, as you said, we may hear exactly why. Oh well, flashaholics and modders are adaptable and we will find ways around. Maybe there is a good reason to it.

Anyway, here is that picture:





Well, looking back at this picture, I noticed that you can see how well the two power contact pads lined up with the traces on the top of the emitter and the vias. Also, you can see on the top of the Rebel how the copper pad that the die is directly attached to fans out a little. It spreads upwards and to the right (I think). This should spread out the heat before it is transmitted through the substrate and then to the thermal pad. I can see what the engineers were thinking now.

evan9162, were you at all interested to see how far the Rebel can be pushed? If you can only secure the LED to a large, fan cooled heatsink, and then up the current some past 2A. It would be cool to know how durable these Rebels really are. If not, that is cool. I would hate to risk destroying such a fine LED, too. I guess that I will have to do the test myself whenever I get some of these. I guess that the Gen-X would be far better suited for this. Overdriving the Gen-X to 3A may become as normal (kind of) as overdriving a XR-E or a K2 to 2A. Well, please continue to test new LEDs as you get them. Have you tested any of the newer Cree XR-E Q-binned LEDs like you did the Rebel yet? If so, can you give links? Wow it is late! Off to bed I go...

-Tony


----------



## pokkuhlag

evan9162 said:


> I don't know what you mean by "unfair", but if you look at the brightness curves and "droop" graphs, you'll notice the only one that's out of sorts is the 50 lumen rebel, and that is due to known heatsinking problems. Since all of the other graphs are in-line with expected results, then the heatsinking for the other test LEDs is sufficient. The cree has a much larger contact patch, so ensuring a very thin epoxy layer isn't as critical.



Like you already know (seen in previous post above this one), ceramic substrate isn't a good heatspreader. The contact of the cree might be big, but the heat will still be concentrated directly under the die (not spreading like a copper heatspreader). Thus having the same problem as the Rebel. 

The droopyness factor shows that rebel is very "droopy", but if all the tests uses the same thickness epoxy layer. The droopyness can be comparable with each other. The droopyness will probably go further down, but it is using the same conditions.


----------



## evan9162

pokkuhlag said:


> Like you already know (seen in previous post above this one), ceramic substrate isn't a good heatspreader. The contact of the cree might be big, but the heat will still be concentrated directly under the die (not spreading like a copper heatspreader). Thus having the same problem as the Rebel.



No, not really.

The cree has a layer of copper directly under the die attach to spread heat out over the top surface of the ceramic. In addition, the thermal pad on the bottom also serves to spreads heat out further. The cree definitely does not have as much of a "hot spot" as the rebel does due to the two larger pad areas.

The cree thermal pad area is 5.6x6.5mm (36.4mm^2), whereas the rebel thermal pad area is 1.8x2.7mm (4.86mm^2). The cree thermal pad is 8x as large as the rebel's, and thus, thermal interface material thickness is less critical than for a rebel. Since the cree does not droop any more or less than other devices, then it has sufficient cooling and a thin enough layer to not matter. I can confirm this in that the cree's Vf does not drop rapidly at high current.


----------



## SemiMan

johnny13oi said:


> Would the heat from a soldering iron kill the emitter? I always that extreme temps would kill any LED emitter.



The goal is to place the emitters just as soon as the solder on the metal core board melts. Essentially I heat up the whole board and then quickly place the emitters. So far so good. I think these things are pretty robust.


----------



## dabiscake

Ditto on that! I was just wondering about that McR-8 reflectors, described on the Shoppe as designed for "surface mount Nichias".. I'm not familiar with those leds, but could they have a similar profile as the Rebels, thus making this reflector the first available output option for the Rebel?
Sorry for the hijacking the thread! Does anybody know of a discussion elsewhere about these reflectors?

Thanks.



Gryloc said:


> McGizmo,
> 
> Sorry this is not the correct thread, but can you give some more information about this Rebel reflector in your "McGizmo" zone of CPF? I had some questions about it and how it compared to your old McR8. It sounds great. Finally an optic/reflector that takes advantage of the Rebel's small size! I also had some technical questions about the reflector for the Rebel. Thank you.
> 
> -Tony


----------



## shiftd

Jarhead did some rebel testing where he pump as much as 2 amps to the rebel. Here is the detailed page

http://www.molalla.net/~leeper/rebel.htm






Gryloc said:


> Hmmm, as for why they did that, as you said, we may hear exactly why. Oh well, flashaholics and modders are adaptable and we will find ways around. Maybe there is a good reason to it.
> 
> Anyway, here is that picture:
> 
> 
> 
> 
> 
> Well, looking back at this picture, I noticed that you can see how well the two power contact pads lined up with the traces on the top of the emitter and the vias. Also, you can see on the top of the Rebel how the copper pad that the die is directly attached to fans out a little. It spreads upwards and to the right (I think). This should spread out the heat before it is transmitted through the substrate and then to the thermal pad. I can see what the engineers were thinking now.
> 
> evan9162, were you at all interested to see how far the Rebel can be pushed? If you can only secure the LED to a large, fan cooled heatsink, and then up the current some past 2A. It would be cool to know how durable these Rebels really are. If not, that is cool. I would hate to risk destroying such a fine LED, too. I guess that I will have to do the test myself whenever I get some of these. I guess that the Gen-X would be far better suited for this. Overdriving the Gen-X to 3A may become as normal (kind of) as overdriving a XR-E or a K2 to 2A. Well, please continue to test new LEDs as you get them. Have you tested any of the newer Cree XR-E Q-binned LEDs like you did the Rebel yet? If so, can you give links? Wow it is late! Off to bed I go...
> 
> -Tony


----------



## Gryloc

Oh wow! I didn't know Newbie did tests to the Rebel that long ago (June 17). I am glad that the Rebel 0100 parts improved since his test. Maybe he was very conservative with his numbers. Looking at the close-up pictures of his 0100 Rebel, the phosphor lightly dusted what were supposed to be the clean "white" ceramic substrate area. Maybe they used the "older" phosphors or something with his Rebel. Does anyone know when they started using these new phosphors? Is it when the 0100 parts came out or when the 0070 and 0080 parts were released (maybe the same die used in the 0040 and 0050 Rebels, but the new phosphor)? Hmmm. It is so interesting to see the parts develop. Thanks for posting that link. I need to check his website more often!

-Tony


----------



## havand

Gryloc said:


> Oh wow! I didn't know Newbie did tests to the Rebel that long ago (June 17).
> 
> -Tony




Site says July 17th. (Today)


----------



## Gryloc

Well, thanks for catching that. I am such a doofus!  Ignore much of my last post then! In that case, why did his samples test the way they did? I thought that Lumileds said that the 0100 part had a minimum of 100lm at 350mA and 180lm at 700mA. Did he receive a worse batch? So, if we had to use these numbers for our next Rebel project, then who has the "better" results, Newbie or Evan9162? I understand that neither can be wrong, but I wonder who has the most realistic figures? This is sort of a bummer. Oh well.

-Tony


----------



## LukeA

Gryloc said:


> Well, thanks for catching that. I am such a doofus!  Ignore much of my last post then! In that case, why did his samples test the way they did? I thought that Lumileds said that the 0100 part had a minimum of 100lm at 350mA and 180lm at 700mA. Did he receive a worse batch? So, if we had to use these numbers for our next Rebel project, then who has the "better" results, Newbie or Evan9162? I understand that neither can be wrong, but I wonder who has the most realistic figures? This is sort of a bummer. Oh well.
> 
> -Tony



There may just be some error in his method. 7 lumens may be within the margin of error in his testing, however I must confess that I know little of his procedures.


----------



## evan9162

There's something amiss with Newbie's sample, or the heatsinking for it. His sample did not scale the same mine did with regards to brightness, and he recorded far higher temperatures at 1A than I did at 2A. At 2A, the top of the dome of my rebel was only at 60C, but at 1A, his was at 83C. That tells me there's a heatsinking problem or something.


----------



## eyeeatingfish

I have a little trouble reading the graphs. Were they saying the new Rebels were brighter than the CREEs?
Did any of the data say which were more efficient, the Rebel or the CREE?


----------



## SemiMan

Based on my samples, the Rebel is probably about a Q4 bin for brightness when you look at output at 350mA, however, the Rebel has a better forward voltage at least for my samples (<3V) so it may be on the order of the Q5 for efficiency. The Cree has better heat sinking so it may behave better over temperature. It is a few C/watt better at the package level and I think I may add another C\watt at the system level.

The Rebel is rated to a higher temp and better life over temperature so maybe we can drive them harder without fear of failure, though I am worried about the heat sinking.

Semiman


----------



## shiftd

In his updated site (here: http://www.molalla.net/~leeper/rebel.htm), Newbie tries to explain the discrepancies in the temperature reading. It is probably better if you look at his writings as I cannot explain it better than him. 

anyway, a snipet

"... Basically one LED admittedly had a thick layer of epoxy under it, where as the other was carefully preped to make the layer as thin as possible- which happened to be the Rebel. Again, doing this, one is comparing apples and oranges, both should have the same mounting technique, or it places the results in the realm of suspect. Most especially with higher thermal resistance materials like thermal epoxy. If the epoxy is kept thin in one case, it is just as important to keep it thin in the other case, otherwise the test setup is *quite suspect*."


----------



## eyeeatingfish

Can someone simplyify the meaning of all of this science stuff about the rebel please?


----------



## Thujone

eyeeatingfish said:


> Can someone simplyify the meaning of all of this science stuff about the rebel please?



electricity in => light out


----------



## matrixshaman

Nice work - very impressive detail on the rebel. Thanks for all your work evan9162 ! I'm looking forward to what these will produce in the way of lights in the next year. I'm wondering how long incandescents will still have any advantage.


----------



## easilyled

Just wondering whether you used the Seoul-P4-U-bins with "H" Vfs for your
comparisons?

I can't remember off the top of my head what the Vf rating is for the H's
but its pretty low.

These ones may compete more favourably with the 100 lumen Rebel
compared to SSC-P4-Us with higher Vfs.


----------



## eyeeatingfish

So how does the Rebel rate in terms of brightness and efficieny to the luxeons, and the CRee/P4s?


----------



## easilyled

eyeeatingfish said:


> So how does the Rebel rate in terms of brightness and efficieny to the luxeons, and the CRee/P4s?



Have you read this thread?


----------



## eyeeatingfish

Im confused at what all the charts mean.


----------



## IMSabbel

easilyled said:


> Have you read this thread?



Be fair, there is NO comparison between a modern cree and the new rebel.

The only graphs are with a cree marked "old version".

Plus there is NO graph that shows efficiency. The only one has lumen/ma, which doesnt consider the forward voltage.

I guess a plain nice lm vs Watt for reben, p4, x-re would be nice.


----------



## LukeA

IMSabbel said:


> Be fair, there is NO comparison between a modern cree and the new rebel.
> 
> The only graphs are with a cree marked "old version".
> 
> Plus there is NO graph that shows efficiency. The only one has lumen/ma, which doesnt consider the forward voltage.
> 
> I guess a plain nice lm vs Watt for reben, p4, x-re would be nice.



With the Rebel's Vf, it's comprable to a high-end Cree Q5.


----------



## evan9162

IMSabbel said:


> Be fair, there is NO comparison between a modern cree and the new rebel.
> 
> The only graphs are with a cree marked "old version".
> 
> Plus there is NO graph that shows efficiency. The only one has lumen/ma, which doesnt consider the forward voltage.
> 
> I guess a plain nice lm vs Watt for reben, p4, x-re would be nice.




There are no graphs with a cree marked "old version". "old version" does not appear anywhere. I tested with a P4 XR-E because that's what I happen to have here. If you would like to send me a Q4 or Q5 cree to test, I'm more than willing to add it to the results. 

The droopyness graph was to explore an aspect of the rebel that was expected (claimed "anti-droop" improvements). It's not even a lm/mA graph as you claim, it's a relative lm/W graph, showing how relative efficiency drops as the current increases. 

I figured it was straightforward enough to see that lower Vf + Higher output = higher lm/W. But since I was apparently wrong about that:


----------



## McGizmo

For *a* single data point, I just compared a single Rebel (100 lumen) to a single Seoul P4 (UW0I), single new K2 and single Cree XR-E (Q4WG) in my integrating sphere. All LED's were introduced to the IS in as close to similar fashion as possible. I took my readings in about the same time lapse from cold start but I won't claim that I caught the LED's all at the same temperature and Vf and Flux *is* a function of temperature!

I tested the 4 LED's at drive current levels of 350, 500, 750 and 1000 mA. The single samples of Seoul P4 and Rebel 100 were within a couple lumens of eachother at all drive levels and their respective Vf's were within less than a tenth of a volt of eachother at all drive levels. These two samples would seem to suggest that there is a reasonable parity between the two and possibly among the population as a whole. :shrug:

The K2 demonstrated similar Vf with the Rebel and Seoul and this in itself is a major improvement over any K2's I have tested in the past. Since the new K2 reportedly uses the same die as the Rebel, one would expect similar performance if the packaging were on par. The K2 tested was about 16%-12% below the Rebel and Seoul in terms of flux. The K2 closed the gap at higher currents.

The XR-E Q4 sample I tested shared similar Vf to the other 3 (less than 1 tenth of a volt difference across the range) but it surpassed the Rebel and Seoul in flux by about 20% going up to 25% at the higher currents.

My testing was quick and crude and of course I have no idea how my measured lumens would map against the true flux measures. I believe the relative comparisons do have strength.

At 1000 mA, all LED's have a Vf of 3.8 +/- .05V. Their measured flux (lumens):

Rebel 100 - 198
Seoul P4 - 198
New K2 - 170
XR-E (Q4)- 246

As I see it, Lumileds is still ramping up with the Rebel and K2 and I have no idea of where these LED's will settle down to in terms of typical performance. The Cree XR-E seems to be evolving quite nicely and it was said early on that the EZ1000 chip was a beast with potential yet to be harnessed by its packaging. It seemed that Seoul obtained some good quality EZ1000 dice early on or perhaps they just did a really good job of unleashing some of the chip's potential quickly?!? :shrug: :thinking: I wonder if we will see a jump in flux with the Seoul as we recently have seen with the XR-E? 

At this point, I feel that Lumileds has again entered the race and if one starts factoring other considerations in beyond that of efficacy, it gets more confusing as to who has the better LED. For the market at large, there is serious weight attached to things such as price, lumen maintenance, consistancy and availablilty of tint and its control, thermal and electrical considerations in mounting of the LED's and of course the quality and nature of the raw light output and distribution and how it can be managed by additional secondary optics.

I don't know if the Rebel is a rebel but it sure represents some "trouble" for the industry! :nana:

Good news: there are options
Bad news: there are options


----------



## Anglepoise

Don......Thanks for going to all that trouble. Much appreciated.

What you refer to as the 'new K2'. Is this the much talked about Gen X by any chance??


----------



## evan9162

Don,

Do you have the 350, 500, and 750mA numbers handy for your tests as well?

Thanks,


----------



## McGizmo

David,

The K2 is identified as next generation K2 in some photo copied spec sheets that accompanied the samples. I can't identify the particular samples by part number and presumed "bin" on the parts relative topart numbers identified in the spec sheet. I get the impression that Lumileds doesn't have their ducks all in a row yet on these parts. I would guess that this K2 is the one you mention but it is a guess.

evan9162,

It's dificult to table this info here in a post so instead, I uploaded a PDF from an Excel file, HERE.

Again, this is a crude measure of single sample LED's so its relevance and significance as applied to the whole populations of these LED's is certainly suspect!

In all of these tested, after ramping the power supply up to 1000 mA, I took it back 350 mA and compared the readings of the warmer LED to the initial readings of the cooler LED. I did see lower Vf as well as lower flux measures. A more reasonable but more tedious test would have involved adding a thermocouple at the root of the die slug and charting Vf, flux as it related to temperature. It would be more reasonable to not only get a feel for how temp effects the various LEDs but to compare their properties at a similar temperature as well. My basis for comparison at present is dependant on taking the various measures in roughtly the same elapsed time from cold start on each of the LED's. I didn't actually time myself nor can I be certain that the die temp would rise at the same rate for the samples.


----------



## Curious_character

Thanks for the super review, with good quantitative data.

It shows that it might be worthwhile to swap an SSC for a Rebel in some applications. I'm thinking of lights which are designed for using two CR123A cells but will run from a single 18650 or 17670 Li-ion cell. These typically have buck regulators. In the few I've tested, the regulator typically drops out when the battery voltage drops below something like 3.8 or 3.9 volts, or roughly 0.3 to 0.4 volt above the LED voltage. Below this, they're essentially direct drive. This transition point falls unfortunately near the beginning of the discharge of the Li-ion cell, and the light is unregulated during the remainder -- nearly the whole discharge period.

If we have an LED with a 0.4 volt or so lower forward voltage, we'd get much farther into the discharge before the regulator drops out. So by replacing the SSC (or Luxeon) with a Rebel, we should get regulated operation for most of the battery discharge period, rather than for just a little time at the beginning.

I haven't yet gotten my hands on a Rebel to try this out, but I'm looking forward to doing it.

I'm also wondering if the smaller emitter might result in a tighter beam, particularly in very small flashlights like an L0P, or even AA size ones.

c_c


----------



## evan9162

Only the physical package of the rebel is smaller than other Luxeons. The die and phosphor (which actually emits light) is the same size - 1mm x 1mm.

The rebel will probably have a slightly smaller emission pattern than a Seoul P4, but that's due to the phosphor deposition technique that the Seoul uses - phosphor is more "globbed" on the seoul than it is on the rebel/other Luxeons. Hence, it does not focus as tightly in a given reflector.

Even though they are nice and bright, I'm still not too keen on the Rebels. They are very difficult to mount/use. I'm also not too fond of the beam pattern of the Crees either (relatively narrow, and not optimal for most reflectors I use), but I think for area lighting with no optics, they're probably the best bet. The positive slug, and some QC/lifetime questions have me hesitant about the Seoul P4, and they seem to be quite delicate when it comes to the silicone dome (bond wires seem to get broken very easily). Then of course, there's the K2, which is still stuck a generation behind everyone else in terms of brightness, but has good reliability, durability, and packaging. 

So I've played around with each of them, and am still left shrugging my shoulders as to what to really use. My real focus should be to use the piles of LEDs I've already acquired, and not get any new ones for a while...heh.


----------



## Curious_character

evan9162 said:


> Only the physical package of the rebel is smaller than other Luxeons. The die and phosphor (which actually emits light) is the same size - 1mm x 1mm. . .


Thanks for the info. There goes my theory on sharper focus due to smaller size. . .

c_c


----------



## IsaacHayes

Yep trade offs. I have different emitters in different lights because some are more suited for other things. Good point about all the old emitters piling up now... I figure I'll make a big lantern with them at some point, running them all at low current for the most lm/w while still being bright. Or make a mains powered thing...

There isn't one end all emitter IMO because there are different end goals and target uses for them.


----------



## Gryloc

It is good of you to to show all the weaknesses of all the lights. It makes you wonder where that perfect LED really is. The XR-E has the latest and brightest dies available, the Seoul P4 most resembles the beloved Luxeon emitter, and the K2 is unusually tough. I say that once someone combines all these aspects, we will be in LED heaven. That is why I am not going to take much crap from those wanting to slam the new Generation X (or "new K2") emitters before they are even out. Those will be tough, bright and focus with any reflector. The only problem I see with these are the long wait....

Anyway, the Rebel has potential. They are a decent alternative to other high efficiency LEDs, and they start at a good price. Their size will allow them to be used in places you never though of before. I can see how it may be tough to work with. That is okay since it was designed to be used for other applications than flashlights. I know of some good uses for them, and I hope to try them out soon. I say that once Lumileds introduces the new emitter, they should not drop the Rebel. The Rebel should grow and develop at the same rate as the new K2. This way you have two brother products using two different sized packages (each with their own applications) with the same great die.

I say that if Lumileds wants to get ahead of the rest, they should re-release the K2s using the new Rebel binning structure, and start to slap the Rebel dies into them. Then, once they develop their new, super-efficient die, they can easily begin to incorporate that die in the K2 package to replace the Rebel dies. They would gain so much more money since they have a wider product range using more efficient dies, and they will help themselves by working out the kinks in the K2 way before the new Generation X dies/emitters are ready. A win-win situation! From there, they can constantly make transitions to the part by upgrading the die. The K2 shape could also be shrunken a little in width and depth, or maybe just height, since the dome lens can be made smaller because there is no need for the long, space hogging bond wires anymore. This is why the dome of the Rebel is so small. They better not call the finished product that is from the Generation X the "New K2" since the K2 name is, unfortunately, scarred. Now, if I was only in charge of the company or had connections...

There I go again. Well, atleast I can dream, right? Maybe Lumileds have more money than we think, and they can afford to mosey around and release their products slowly. If only Lumiled can hear us here at the CPF, or begin to listen to us! Oh, well. I will stay optimistic, though.

-Tony


----------



## LukeA

Curious_character said:


> Thanks for the info. There goes my theory on sharper focus due to smaller size. . .
> 
> c_c



That info's been available for weeks.


----------



## Curious_character

LukeA said:


> That info's been available for weeks.


There's a vast amount of information which has been available even for centuries that I'm not aware of! But thanks to the gentle CPF members who have the time and patience to humor me in my ignorance, the holes get filled in one speck at a time. And I keep trying to do my best to return the favor.

c_c


----------



## Empath

A couple of off-topic posts were moved to their own thread in a different forum.


----------



## kanarie

Here is a German site with a comparison and photo's 
lhttp://www.ledstyles.de/ftopic1830.html


----------



## Oznog

Wow, the Cree XR-E sure looks like it's beating the Rebel 100 here, and the Cree is running on slightly less power to boot. They both look well-heatsinked too so I see no reason to believe it's because the Rebel's running hotter.

Babelfish is providing an "interesting" translation, as usual.


----------



## LukeA

kanarie said:


> Here is a German site with a comparison and photo's
> lhttp://www.ledstyles.de/ftopic1830.html



Are those emitters running in parallel? In any case, that Cree's not exactly whipping the Rebel.


----------



## Gryloc

Owww, my head hurts!!!  That was a lousy translation. I tried to read the whole thread and I tried to comprehend it. Babel Fish was the same way. You would think they would have translated German better. Is there any native Germans or German speakers that can help us here?

Unfortunately, I do not think that you can conclude anything from those tests! First, as LukeA noticed, they were run together in series. I cannot think right now, but can a LED with a lower Vf allow it to take more of the power than the other series-attached LED? I know that can happen when in parallel. I wish I knew what power supply they used and what circuitry (if any) was used (standard wall adapter, battery pack, regulation circuit?). I was hoping that each would be driven completely separate for such a critical comparison.

Second, you can not judge strictly by pictures taken with the typical digital camera which is brighter. The camera was so overloaded, and the amount of streaky glare that resulted does not mean anything. The paper tests did not help any, either. I do not trust any rough eye-ball guesses and opinion on which two LEDs are brighter until I see lux or lumen figures, or even some beamshots. The two LEDs are so different because the XR-E has a weird radiation pattern, so the apparent brightness at one angle can be misleading.

What does everyone else think? I think that I am going to lay down a little to get some relief... :green:

-Tony


----------



## evan9162

Their rebel is mounted on a star board. I have my doubts about the thermal performance of the rebel stars. Lumileds' official stars for the K2 add 4C/W to the total thermal resistance. The 3rd party star boards probably add a lot more than that. The rebel datasheet shows a recommended thermal via pattern for the rebel PCB, and even with thermal vias, the thermal resistance to the backside of the PCB is 7C/W. 

So it doesn't matter how big of a heat sink you use - if the thermal interface between the LED and the heat sink is poor, then the LED will heat up a lot, and you'll get lousy performance. 

Plus, their side shot isn't very telling. The rebel and XR-E have different beam profiles - you can't really compare them directly and say one is brighter than the other.


----------



## Oznog

Gryloc said:


> Unfortunately, I do not think that you can conclude anything from those tests! First, as LukeA noticed, they were run together in series. I cannot think right now, but can a LED with a lower Vf allow it to take more of the power than the other series-attached LED? I know that can happen when in parallel. I wish I knew what power supply they used and what circuitry (if any) was used (standard wall adapter, battery pack, regulation circuit?). I was hoping that each would be driven completely separate for such a critical comparison.
> 
> Second, you can not judge strictly by pictures taken with the typical digital camera which is brighter.



Of course! Any two devices in series always have the same current, by like the most basic electrical laws. So setting up a ballast or other constant-current source will ensure both devices get 700mA or 1000mA or whatever. That was the ideal way to do it. Putting LEDs in _parallel_ without individual ballast resistors is disasterous.

The camera overloading was apparent in the first pics, but when shown on the paper I didn't see the overloading. The "dot" pic's circumstances are unclear but the camera doesn't look saturated to me.


----------



## kanarie

I can read German:
They conclude that the Cree P3/P4 still can stand up to the Rebel very well . Also that the Cree has more light coming from the top the Rebel more from the side and that efficiency of the Rebel is best between 350-700 mAh
above 1000 mAh the Cree is more efficient.

Also it looks like they took the factsheet and tried to match their test results to it(refering to it all the time).
I also have some reservations about their test setup (but I could not resist to share the link :devil: )


----------



## SemiMan

Curious_character said:


> Thanks for the info. There goes my theory on sharper focus due to smaller size. . .
> 
> c_c



It is not so much the die size as the effective optical source size that matters. The effective optical source size of the Rebel from what I can figure out is smaller than other Luxes or Seoul so your sharper focus theory may in fact still be true.

Semiman


----------



## LukeA

Curious_character said:


> There's a vast amount of information which has been available even for centuries that I'm not aware of! But thanks to the gentle CPF members who have the time and patience to humor me in my ignorance, the holes get filled in one speck at a time. And I keep trying to do my best to return the favor.
> 
> c_c


Sometimes I forget that most people don't study all the Rebel-related threads as thoroughly as I do.


----------



## Gryloc

Semiman,

You know, that is what I was thinking, too. You mean the "apparent" size of the die looking through the built on primary optics (the dome)? I wish I have some Rebels in front of me so I can turn it every direction to see that the dome does to the die. Fortunately, I ordered some and they are on their way. Until then, I wonder if the "apparent" die size is that much smaller. I know that it is much more different than any Luxeons, XR-Es, and Seouls. From the very _top_ view of each LED (which is a view most reflectors will never see -maybe optics), the "apparent" die size looks about the same.





Hopefully it is okay if I use some people's pictures. I just collect a bunch of pictures from the CPF (sometimes because of some beautiful shots of power LEDs and lights). This is a very poor comparison between the LEDs and the "apparent" die size _from the top_.

I know from the sizes, at angles, the small dome of the Rebel seems to distort the image of the die much more than the dome from a Luxeon or Seoul. Obviously, the XR-E is a completely different species because of that dang glass dome...

I guess that it is best to compare those radiation pattern diagrams that are given on every datasheet, and use that in addition to comparing the "apparent" die size at every angle. Somehow, this may help us determine if the LED die will appear smaller when used with reflectors and TIR optics. Maybe the only way to compare them is to use each LED in a medium sized, smooth reflector (at the exact focal point -if possible), and take very good, short exposure beamshots to compare the final hotspot size. This will be tough to do so few may attempt it. I guess that the "apparent" die size of the Rebel will become purely subjective.

I know that I will have to "modify" some of the LEDs to get an even smaller "apparent" die size. One way to do this is to remove the soft dome from the rebel without ripping off any phosphor, or by taking the dome and ring off of the XR-E. Newbie took off the dome from his newer Rebels (using the different phosphor coating from the older types) without removing any phosphor from the die. Maybe that can be repeatable. Without domes, the LED becomes more "frail", but the apparent die size seems to shrink tremendously! Maybe this will help us when using the Rebel with small, 10mm reflectors (McGizmo's McR reflector). This should hopefully make the hotspot on the beam look smaller. Will this work?

-Tony


----------



## Oznog

I've heard several people here try to comment now on sharpness of the beam would depend on emitter size.

This is incorrect. More specifically the figure you're thinking of is _the ratio of emitter size to lens size_. Also the refractive index of the material used is equally important.

The technical limits of how tight a 1.5" acrylic lens over a 1" sq emitter can be focused are basically the same as a 1.5 mm lens over a 1 mm sq emitter.

The larger XRE looks to have a somewhat larger ratio of emitter to lens size, and as far as I know they're acrylic not silicone. I have no data on what the refractive index of this high-tech silicone might be but AFAIK acrylic has a stronger refractive index.


----------



## evan9162

The XR-E lens is glass
The K2, Seoul P4, and Rebel all have silicone lenses
The Luxeon, Luxeon III, and Luxeon V all have acrylic lenses.

The K2 and Luxeons all have a silicone encapsulent under the lens so the bond wires can flex due to thermal expansion
I think the XR-E does as well
The Seoul P4 may also
However, I'm unsure if the rebel does. Since it does not have bond wires, it seems there might not be the need.


----------



## Gryloc

We debate the size of the die (or the apparent size) because the size of the source compared to the size of the reflector is important to the size of the hotspot. This is why McGizmo was concerned about his McR 10mm reflector and the Rebel, because the beam looked similar to an 'ol Luxeon V mated with an IMS 20mm reflector. It had a very broad beam. The die of a LuxV emitter _looks_ like it is ~3mm wide, compared to the 20mm reflector, while the Rebel die _looks_ like it is ~1.5mm while McGizmo's reflector is 10mm. The real die size of each is ~2/3 of how it appears, of course. As Newbie stated in his findings, the Rebel die is actually a little bigger than the ones in the Cree and Seoul LEDs.

Anyway, the brightness of the beam depends on how the light (of a certain intensity), is focused. Deeper reflectors collaminate more light to make the beam look more intense. Another thing is the projected image brightness. The reflected light cannot have more intensity than the surface brightness of the LED die. In that case, the LuxV has a wider, flatter beam compared to a Cree or Rebel or Seoul with the same overall brightness. More light from smaller area (its surface area) is great news for anyone who wants a good throwing beam.

Optics can play with light so much, too. I think that you can focus light tighter than the size of the optic, but isn't the minimum size of this focused beam the same size of the source? When you want to throw light in a parallel beam, then you are correct that it matters on the size of the optic/reflector. 

I think that you can defocus a beam produced from a back-lit sheet of paper into the size of a speck, but it just depends on the optic. Aspheric concentrating optics can focus things into a spot, but can elliptical reflectors also do this? Of course with these optics, your beam will change a lot depending if your target is near the focal point or not. 

This is stuff most of you should already know, but I thought I would bring it up again. I hope I did not get anything mixed up. This is why I really want to a get a new Rebel 0100 or a XR-E Q5 and remove the primary optics carefully. Then when mated with a big, deep reflector, the spot will be spectacular! They say that these latest high-efficiency LEDs (Cree XR-E and Lumiled's Rebel) have a surface brightness of most HID lighting. I think that if they can make the LED dies the right shape and size to be focused properly, and you will have lights that may compete with HID and incandescent much better. (oh crap I forgot to hit submit -I typed this like an hour ago!)

-Tony


----------



## SemiMan

Gryloc, you are a much bigger gluten for punishment than I am! More to look at the die than anything I removed the dome off a Rebel. Perhaps if I was more careful, I could have saved the bond wires, but it was not to be.

If you remove the dome though will you not lose a lot of the light output? This is an important part of the overall design of the LED (matching indexes of refraction, etc.) I think this is why the Luxeon PWT LEDS put out a lot less light. I wonder if Lumileds plans a newer PWT with this new die or if they will just concentrate on the Rebel?

Semiman



Gryloc said:


> We debate the size of the die (or the apparent size) because the size of the source compared to the size of the reflector is important to the size of the hotspot. This is why McGizmo was concerned about his McR 10mm reflector and the Rebel, because the beam looked similar to an 'ol Luxeon V mated with an IMS 20mm reflector. It had a very broad beam. The die of a LuxV emitter _looks_ like it is ~3mm wide, compared to the 20mm reflector, while the Rebel die _looks_ like it is ~1.5mm while McGizmo's reflector is 10mm. The real die size of each is ~2/3 of how it appears, of course. As Newbie stated in his findings, the Rebel die is actually a little bigger than the ones in the Cree and Seoul LEDs.
> 
> Anyway, the brightness of the beam depends on how the light (of a certain intensity), is focused. Deeper reflectors collaminate more light to make the beam look more intense. Another thing is the projected image brightness. The reflected light cannot have more intensity than the surface brightness of the LED die. In that case, the LuxV has a wider, flatter beam compared to a Cree or Rebel or Seoul with the same overall brightness. More light from smaller area (its surface area) is great news for anyone who wants a good throwing beam.
> 
> Optics can play with light so much, too. I think that you can focus light tighter than the size of the optic, but isn't the minimum size of this focused beam the same size of the source? When you want to throw light in a parallel beam, then you are correct that it matters on the size of the optic/reflector.
> 
> I think that you can defocus a beam produced from a back-lit sheet of paper into the size of a speck, but it just depends on the optic. Aspheric concentrating optics can focus things into a spot, but can elliptical reflectors also do this? Of course with these optics, your beam will change a lot depending if your target is near the focal point or not.
> 
> This is stuff most of you should already know, but I thought I would bring it up again. I hope I did not get anything mixed up. This is why I really want to a get a new Rebel 0100 or a XR-E Q5 and remove the primary optics carefully. Then when mated with a big, deep reflector, the spot will be spectacular! They say that these latest high-efficiency LEDs (Cree XR-E and Lumiled's Rebel) have a surface brightness of most HID lighting. I think that if they can make the LED dies the right shape and size to be focused properly, and you will have lights that may compete with HID and incandescent much better. (oh crap I forgot to hit submit -I typed this like an hour ago!)
> 
> -Tony


----------



## Gryloc

Though with the Rebel there is not bond wires, I haven't thought about the effect of the beam because the dome was removed. I wondered what significance the dome served in the "design" except for protection of the die and to help dissipate heat some. Maybe with refracting some light. Wouldn't it help to remove the dome when using the LED with a reflector, since most light leaves from most LEDs from the top (the radiation pattern/curve)? Maybe this would allow more light to leave evenly, which means more light to be reflected by the reflector? I finally got a variety of Rebels in the mail, so there is a chance something bad may happen when learning to handle these tiny critters. Lets hope a dome shears off cleanly while the phosphors stay in tact. I don't know. It is late and I am not thinking straight...


-Tony


----------



## SemiMan

Doh! This is why I should not do these things at night! No wonder I thought I killed the bond wires, there were non to kill!!

I am pretty certain that without the silicon dome there, as opposed to the light leaving the die, it will just reflect back inside the part as the index of refraction between the die and silicone dome is much different than with air.

I agree that the light emits from the top surface, but it does not exit perpindicular to the surface though I understand there is research in that area. Since the light is not perpindicular, the index of refraction is going to be key between the two materials.

I wonder if that stuff for dissolving silicone bathroom caulking would work without killing the phosphor? I doubt it, but at $2.50 a part it is a low cost experiment.

Semiman



Gryloc said:


> Though with the Rebel there is not bond wires, I haven't thought about the effect of the beam because the dome was removed. I wondered what significance the dome served in the "design" except for protection of the die and to help dissipate heat some. Maybe with refracting some light. Wouldn't it help to remove the dome when using the LED with a reflector, since most light leaves from most LEDs from the top (the radiation pattern/curve)? Maybe this would allow more light to leave evenly, which means more light to be reflected by the reflector? I finally got a variety of Rebels in the mail, so there is a chance something bad may happen when learning to handle these tiny critters. Lets hope a dome shears off cleanly while the phosphors stay in tact. I don't know. It is late and I am not thinking straight...
> 
> 
> -Tony


----------



## martonic

jtr1962 said:


> Even though it appears that the Rebel doesn't use anti-droop technology, the efficiency of 71 lm/W near the maximum rated current is very impressive. This basically means you can use these for home interior lighting, and even including driver losses of 10% of so they will still be better than most CFLs when giving the maximum amount of light per LED. No need to underdrive them at all in the name of efficiency, although if you do you could approach T8 linear tube efficiency. 234 lumens is enough to more than replace a 25 watt small base incandescent (those are horribly inefficient) while using maybe 1/7 of the power.
> 
> I can't wait to get my hands on a few of these so I can run my own testing.


What about operating conditions? The 25 watt small base incandescent is your typical "applicance light" used in everything from freezers at near 0 degrees F to ovens at around 500 F. What happens to LED's in such conditions?


----------



## jtr1962

martonic said:


> What about operating conditions? The 25 watt small base incandescent is your typical "applicance light" used in everything from freezers at near 0 degrees F to ovens at around 500 F. What happens to LED's in such conditions?


Freezers are fine. In fact, since heat is the enemy of LEDs freezer operation is actually better for them. Ovens forget about it. But then again, it's not like most of the energy used for lighting is to light ovens. Incandescent is fine there. As an added bonus, the heat from the bulb just reduces the amount of power used for the primary heating element, so you can't even say incandescent is wasteful in this application. I really think oven lighting might well be the only major use left for incandescent once LEDs go mainstream in a few years.


----------



## BytorJr

Kinda makes me wonder what's going to happen to oven lights when they mandate no "indys."


----------



## TorchBoy

SemiMan said:


> Gryloc, you are a much bigger gluten for punishment than I am!


Brings to mind images of torturing people who have coeliac disease... 



jtr1962 said:


> I really think oven lighting might well be the only major use left for incandescent once LEDs go mainstream in a few years.


I wonder if those people in Australia and New Zealand working on banning incandescent lightbulbs have considered that. :shakehead


----------



## SemiMan

I could foresee a ban on incandescent for even an oven by placing the LED light source behind a two layered window to isolate the LED from the oven heat...similar to what is already on the front of the oven. I will not comment on the cost this will add to the oven or if it is even worth it... but technically it is feasible and would create a permanent hopefully never need to replace light source...until it fails in which case it will cost you $175 to replace it, not $1.

Semiman



jtr1962 said:


> Freezers are fine. In fact, since heat is the enemy of LEDs freezer operation is actually better for them. Ovens forget about it. But then again, it's not like most of the energy used for lighting is to light ovens. Incandescent is fine there. As an added bonus, the heat from the bulb just reduces the amount of power used for the primary heating element, so you can't even say incandescent is wasteful in this application. I really think oven lighting might well be the only major use left for incandescent once LEDs go mainstream in a few years.


----------



## Opto-King

You can also use light guides ... there is no need to have the LED placed where the heat is :shrug:


----------



## jtr1962

I've completed my own testing of the Rebels:




















My relative intensity versus beam angle results are nearly indentical to yours although my calculated lumen output is somewhat less.


----------



## RoGeR

Hmm... Pretty big difference between two Rebel 100.

At 300 mA 85 vs 98 lumens (+15%)
At 700 mA 164 vs 179 lumens (+ 10%)
At 1000 mA 208 vs 234 lumens (+ 12%)

Strange...


----------



## easilyled

RoGeR said:


> Hmm... Pretty big difference between two Rebel 100.
> 
> At 300 mA 85 vs 98 lumens (+15%)
> At 700 mA 164 vs 179 lumens (+ 10%)
> At 1000 mA 208 vs 234 lumens (+ 12%)
> 
> Strange...



No, not at all.

This is the binning info from lumileds:-

The bin I received is NVND. The new binning scheme for Rebels puts these parts as such:

N = 100-120 lumens
VN = Up and to the right of the W0 color bin (see binning chart)
D = 3.03-3.27V Vf

These binning values are at If=350mA.


In other words there is a 16.67% difference between the higher and the
lower value in Lumileds own description.

Then if you take into a/c different testing conditions such as heat-sinking,
temperature and different measuring devices its not strange at all.


----------



## jtr1962

One thing bothering me now is that my angular distribution plot and evan9162's were almost identical, while our lux values where radically different. For example, at 670 mA evan9162 measured 45.8 lux compared to my 64.3 lux at 700 mA. If anything, his lumen calculations should be a lot lower than mine, not higher, _unless_ lux was measured at a greater distance than 1 meter.


----------



## TorchBoy

I don't see what the problem is. Your light meters might have different sensitivities, your LEDs are almost certain to have different efficiencies, and it's just possible your measuring of 1m might also be different. Are your results consistent is the question I would be asking.


----------



## evan9162

jtr1962 said:


> One thing bothering me now is that my angular distribution plot and evan9162's were almost identical, while our lux values where radically different. For example, at 670 mA evan9162 measured 45.8 lux compared to my 64.3 lux at 700 mA. If anything, his lumen calculations should be a lot lower than mine, not higher, _unless_ lux was measured at a greater distance than 1 meter.



I measure lux at 1 meter. 

Perhaps we should examine the lumen integration techniques. I downloaded your spreadsheet and looked at how you were integrating the beam to get a lumen coefficient, and it looked quite different than what I am doing.

What I do is use spherical caps. For the specific angle, I calculate the area of a spherical cap with that angular size, of a sphere if 1 meter. 


I then subtract the previous spherical cap from it, to get the area of a spherical ring. I then multiply that area in square meters by the lux reading (since 1 lux = 1 lumen per squre meter) to get the total lumens emitted in that spherical ring of the beam profile.

I can double check that my spherical ring calculations are proper. If I put 1 as the brightness coefficeint for each offset angle, then the total lumens integrated from 0 to 90 degrees should equal the surface area of half a sphere with a radius of 1 meter. The surface area of a sphere is 4*pi*r^2. Thus, the surface area I should calculate should be 2 pi, and when I plug that into my spreadsheet, I get exactly that, so at least I can double check my geometry.


----------



## evan9162

jtr1962 said:


> One thing bothering me now is that my angular distribution plot and evan9162's were almost identical, while our lux values where radically different. For example, at 670 mA evan9162 measured 45.8 lux compared to my 64.3 lux at 700 mA. If anything, his lumen calculations should be a lot lower than mine, not higher, _unless_ lux was measured at a greater distance than 1 meter.




One more thing that just occured to me. The lux values from my data is the raw reading from my light meter. I have a meter correction factor that I use based on how my light meter compared to the CPF reference lights in the Light Meter testing passaround. That correction factor is used in the lumen calculation. I don't record the corrected lux value so I can quickly reference what my light meter actually says and see in an instant how things might compare when I'm measuring an LED. 

My meter correction factor for white LEDs is 1.46. Thus, the 45.8 lux reading for 670mA is really 66.8 when the correction factor is applied. Thus, our readings are in-line with each other.


----------



## jtr1962

evan9162 said:


> My meter correction factor for white LEDs is 1.46. Thus, the 45.8 lux reading for 670mA is really 66.8 when the correction factor is applied. Thus, our readings are in-line with each other.


OK, so now your calculations make sense. I double checked my spreadsheet calculations. If I put in the numbers for a 360° uniform source my total lumens are exactly 4*pi*(lux at 1 meter), exactly as it should be.

I didn't use correction factors in my calculations because my meter was close to dead on for LED-type light. Also, I started testing LEDs long before the benchmark testing. I wanted to keep consistency between my earlier and my present testing. However, if I were to use the correction factor obtained from the lightmeter benchmark testing (1.116), then my corrected results would be 107.9 lm @ 350 mA, 183.1 lm @ 700mA, and 232.6 lm @ 1000 mA. This is practically identical to your results, in fact amazingly close given that we use different setups and different light meters.

Thanks for helping me get that cleared up. :thumbsup:


----------



## evan9162

jtr1962 said:


> OK, so now your calculations make sense. I double checked my spreadsheet calculations. If I put in the numbers for a 360° uniform source my total lumens are exactly 4*pi*(lux at 1 meter), exactly as it should be.
> 
> I didn't use correction factors in my calculations because my meter was close to dead on for LED-type light. Also, I started testing LEDs long before the benchmark testing. I wanted to keep consistency between my earlier and my present testing. However, if I were to use the correction factor obtained from the lightmeter benchmark testing (1.116), then my corrected results would be 107.9 lm @ 350 mA, 183.1 lm @ 700mA, and 232.6 lm @ 1000 mA. This is practically identical to your results, in fact amazingly close given that we use different setups and different light meters.
> 
> Thanks for helping me get that cleared up. :thumbsup:




No problem. It's quite encouraging to see our results so consistent. It lends credence to our measurement methods. It sounds like your integration method is spot on. One of my high school math teachers had a quote up on his wall - "Truth in mathemetics is consistency". We're getting pretty consistent results, so I'd say our measurements can be held in high regard.


----------



## evan9162

So I upgraded one of my mag mods using a Rebel-100. 

For the last few years, it's had a V-bin Luxeon V. I decided to swap out the LED because the rebel will give a nice increase in output, will focus much tighter, and won't require a silly 6AA battery adapter anymore (this is in a 2D mag). 

The tight focus and brighter output of the rebel is nice, but my god is it a PITA to use. In almost all of my Mag mods, I have a pedistal heat sink where the pedistal diameter is the exact diameter of the hole in the mag reflector. On this particular one, I machined a smaller raised pedistal to experiment with making centerin easier. In order to mount the rebel, and ensure maximum thermal transfer to the heat sink, I ground down a slice of the pedistal, to allow the rebel power contacts to overhang. I then made my own "bond wires" to solder the main power wires to. This both eases assembly, and provides strain relief to prevent any stress on the rebel package due to the larger and stiffer power wires.

Here's the setup:






And showing the overhang:





It was a nice upgrade. Total output increased from 140 lumens to about 230 lumens, and spot brightness increased from 4800 lux to around 30,000 lux. I'm driving the rebel at 1A, vs 780mA for the Lux V.

But it was a ton of work, and resulted in a modification to the heat sink for this light that reduces its usefulness for any other package type. So rebels really need a purpose-built heat sink system, which ends up being incompatible with other LEDs.

On another note, I found something that you *shouldn't* do with a Rebel-100 driven at 1A.

When I want to measure the Vf of an LED when it's installed in a light, I typically cover the dome with a piece of black vinyl electrical tape, power it up, and use my DMM probes to measure the voltage. I do this because of the blinding point of light that typically comes with power LEDs, rendering me blind and unable to make measurements.

I've never had an issue with this...until now.

I proceeded down my normal path attempting to measure the Vf of this rebel I just installed. I hadn't tested this one, so I was curious about the Vf at 1A. I gently dropped the piece of black vinyl tape over the dome of the rebel, turned on the light, and went to reach for my DMM probes.

When I looked back, *smoke was rising from the tape* right where the dome of the rebel is located. The tape started to melt, and the light from the rebel began to blast through. I quickly turned things off, cursed a few times, removed the mangled tape from the rebel, and checked for damage. There was a small smudge on the dome, which quickly cleaned up with some isopropyl alcohol. I checked the brightness, which measured exactly the same as before, so I knew there wasn't any damage done.

Now, this isn't exactly what you think. The rebel did not really get very hot - it's very well heat sinked, so this didn't happen because the rebel its self was physically heating up. 

In this case, *the energy in the light emitted by the rebel caused the black tape to melt and smoke*. Tons of white light hitting a black surface will cause it to heat up. When it's something like vinyl electrical tape, this will happen:






Now, this isn't because the rebel outputs more than a comparable power LED like the XR-E. This is a result of the extremely tiny optical dome of the rebel. The optical dome of the XR-E is around 5mm in diameter, whereas the rebel's dome is around 2.5mm in diameter. In addition, the rebel dome is substantially closer to the die than the XR-E dome. 

What this means is that the light intensity at the top of the dome of the rebel is probably 5-10x that of the XR-E, and anything right at the dome of the rebel is receiving that same ratio of optical energy per unit area vs. an XR-E of the same overall brightness. 

So placing something dark or even modestly absorbent (like a finger) right on the dome of a fully cranked up rebel could result in things heating up VERY quickly. And no, I'm not about to stick my finger on this one and turn it on just to see what happens


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## jtr1962

evan9162 said:


> And no, I'm not about to stick my finger on this one and turn it on just to see what happens


I actually _did_ do that and my finger got pretty hot quite fast. And I'm fairly light-skinned. Regardless of skin color, this is not something I would recommend. Nevertheless, this and your black tape experience shows what an incredible amount of light energy the Rebel is emitting. Figure at 1 amp it's putting out around 235+ lumens. At 330 lm/W efficacy of the emitted spectrum that's nearly three-quarters of a watt of light energy coming from a very small area. Knowing how hot something of similar size, like an 0805 resistor, can get when dissipating that much energy, it's no surprise what happens to the tape (or my finger).

BTW, my finger gets hot over a Cree also, but not anywhere near as hot as over a Rebel. When these things start approaching 75% efficiency and running at power levels of 10 watts or more they'll probably be able to start fires just like high-power incandescents can now. Ouch!


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## Gryloc

Evan,

Thank you for sharing your project and your stories. I have planned on doing the same to a 2C Maglite, but I am still waiting on the Rebel 0100 from the shoppe and my heatsink from Litemania. I am very happy to hear that you got a boost in lumens, and due to the single die, a huge increase in lux.

In my 2C light, I found some cheap buck drivers that I could hook in parrallel to deliver from 1.6A or 2.0A to my Rebel 0100 from two li-ion cells. So if you can get 30K lux, I wonder what would happen at up to twice the current. I agree that the beam from a single die emitter with a big Mag reflector is so narrow that it limits its tasks. For me, I just want this to be my super beast for show, and that is it. I have lights that are more useful for daily tasks.

Your electrical tape incident was interesting. I am afraid of putting anything close to my Rebel emitters for that reason. I have already burned myself a few times by touching my finger against the dome of the Rebel emitter or holding it near by. It is neat to feel all of the light energy that exits the LED die, knowing that the LED is well heat sinked. One flashlight that I have uses 4 Rebel 0090 emitters in a tight array, and I have to be extremely careful around those emitters because it is easy to burn yourself with that those four emitters. 

I may have to try to cut part of the C-sized heatsink like how you did for the Rebel, otherwise I would have to epoxy the whole thing down and solder wires to the top of the emitter, which looks kind of sloppy. Well, if I expect to use any "new K2" emitters, maybe I should not cut anything. Rebels are awesome, but for large flashlights, larger emitters would be better suited, especially if powered at up to 2A.

Thank you for sharing your experiences and showing us a few pictures. Once I get my parts in and hooked up, I may post my results as well. I hope to do some long term testing (not consecutive hours, for heat and cell life reasons) on this light to see how the Rebels like 2 amps. Laser folks, watch out! We have high power light emitting devices that can also cut through thin plastic film and tape (even though we cannot do it at 1 meter away). 

-Tony


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## frenzee

The light exiting a rebel 100 running on 1A (at the surface of the die) is roughly 500 times more intense than noon time sun. You can actually feel the heat if you hold your hand a few centimeters in front of the emitter. Using sunglasses when running at these hight currents, I think is a must.

As an aside, I just learned that the cool white rebel 100 production has been pushed back to next Feb.


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## skalomax

Thanks for the info, Does this mean that the rebel does indeed throw farther In a bigger reflector than a Seoul or Cree?


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## evan9162

It will indeed throw farther than a Seoul, since the P4's phosphor application results in a bit of a glob. This increases the size of the light source, which will not focus as tight.

As for the Cree, the beam profile of the XR-E and Rebel are substantially different from each other. The XR-E projects forward much more than the Rebel, so in a shallow reflector, and given equal output, the Rebel should throw farther since a larger percentage of the emitted light hits the reflector. However, I don't really know how they would compare in a sufficiently deep reflector that would make better use of the XR-E's beam profile.


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## koala

I tried the Rebel once in a Mag reflector, the hotspot is quite small. So I assume it will throw further because more light is concentrated in the center.


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## evan9162

I've also found that the rebel produces an unusually small hotspot in a Mag reflector.

In fact, the hotspot is even smaller than with a Lux III or K2, which is interesting, since they all have the same die size, and thus you'd expect them to behave nearly identically with the same reflector. The difference must be be the optical effect that the rebel's tiny dome has vs. the larger dome of the Lux III/K2.


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## skalomax

Thanks for the info evan.

:thumbsup:


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## Lightingguy321

According to a very recent email reply from a Lumileds rep, the Rebel RB100 LXML-PWC1-100 is going to be out of stock until Q1 of 2008. This could mean one of two things, they are turning the rebel into the first Gen X available to the public, or 2 demand was so high that they have completely ran out of stock. I believe it is both reasons but we will have to wait and see come 2008.


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## evan9162

From what I understand, the Rebel-100 has seen huge demand. Lumileds is probably funnelling all of its output to its teir-1 customers.

Not too bad of a problem for Lumileds to have.


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## koala

That's not an issue in Australia, or Asia  :nana:, yes there's slight shortage but I could still get them. No tint info though .


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## frenzee

I heard that they are having production and performance/reliability (not capacity) problems with the Rebel-100 as well as the high-bin reds rebels. My guess is they are re-tooling their manufacturing process to get more product consistency. I also heard that they don't recommend Rebel-100 for design work. To me, this suggest the rebel-100 we see some time in Feb. (fingers crossed) may well be a different animal.


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## evan9162

Where did you hear this from?

I thought we had already established that the 40 lumen red rebel was unavailable due to demand, and not due to production issues:

https://www.candlepowerforums.com/threads/174250


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## frenzee

I really hope that it's just a demand issue. I'm just telling what I've heard from my Lumileds rep. However, the "not recommended for design" has also been used with regard to the 40lm red. In any case, I have confidence in Lumileds as a compaby and am optimistic in their being able to overcome the challenges, be it demand or production.


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## evan9162

Given corporate culture, I have a hard time believing that a sales representative would be allowed to tell a customer that they are having production problems without facing reprimand from their company. 

That is completely counter to how sales reps are usually allowed to disseminate information. Production issues are usually company confidential information, and reps are usually not allowed to comment on any issues - they are normally only supposed to relay what kind of lead time there is on the product.


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## Bassmann

frenzee said:


> I heard that they are having production and performance/reliability (not capacity) problems with the Rebel-100 as well as the high-bin reds rebels. My guess is they are re-tooling their manufacturing process to get more product consistency. I also heard that they don't recommend Rebel-100 for design work. To me, this suggest the rebel-100 we see some time in Feb. (fingers crossed) may well be a different animal.


 

My english is really poor but i Try to explain what i Know: They run out+Production Problems( as far as its wright they got some new Product Lines)+Pressure from some bigger Companys that Philips is breaking Contract because they can not deliver that much Rebel 0100 as they said, also the 0100 will be replaced with the new 0120 - 0160, what seems to be the Bin that Evan9162 got( a little over 150Lumen). Shipping should be December 07. 


The Rebels 0100 i own are not as bright as the 1 you guys got.....


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## frenzee

So you think there is a 120lm/W rebel on the horizon? And that it might start shipping in December? If I understand you correctly, I think I know what I want for Christmas this year!


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## evan9162

Bassmann said:


> 0100 will be replaced with the new 0120 - 0160, what seems to be the Bin that Evan9162 got( a little over 150Lumen).



Where do you conclude that I got an unreleased bin? I bought 100 lumen rebels on the day they were announced, back in July, from Future Electronics. The part I tested was 100 lumens at 350mA, which is exactly how it's performing. Why do you think I got some other part?

Are you sure you got a Rebel 100? Some places are selling rebels, but quoting their output at 700mA (~95 lumens for the Rebel 50, over 100 for the rebel 70). You might have gotten some other part due to clever advertising on the seller's part.


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## Bassmann

frenzee said:


> So you think there is a 120lm/W rebel on the horizon? And that it might start shipping in December? If I understand you correctly, I think I know what I want for Christmas this year!


 

This was just the Info we got from Philips Germany, most times he ist telling the truth. We phone sometimes to get some Info about new Products for our Light solutions.

@Evan 9162, yes i'm shure i own a 0100 Rebel( Philips Pruducts are direct from Philips/ Cree are direct from Vossloh-Schwabe) : 3,[email protected] - 100~105lm. 3,[email protected]~200lm Those tests are on finished Products.

But you are right, i just didnt look exactly.


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