# The brightest LEDs for micro flashlights



## mailint (Sep 25, 2007)

Am I correct in assuming that the brightest LEDs currently on the market to be used for micro-flashlights are the following?


Cree XLamp 7090 XR-E Cool White - performance group: Q5 (probable product code: 00XREWHT-L1-WG-Q5-0-01)
diameter: 6.80mm
minimum luminous flux: 107lm @350mA
relative intensity @900mA: ~215% (100% = intensity @350mA)
source: http://www.cree.com/products/pdf/XLamp7090XR-E.pdf and http://www.cree.com/products/pdf/XLamp7090XR-E_B&L.pdf

Philips Lumiled LUXEON Rebel Cool White - performance group: part number LXML-PWC1-0100
diameter: 3.17mm
minimum luminous flux: 100lm @350mA - 180lm @700mA
drive currents: 350 to 1000mA
relative intensity @1400: very approx (because out of graph!) 235% (100% = intensity @350mA)
source: http://www.philipslumileds.com/pdfs/DS56.pdf

Seoul Semiconductors Co. (SSC) Z-Power (P4 series) (Pure White) - performance group: part number W42180-U
diameter: 7.40mm
minimum luminous flux: 91lm @350mA (240lm @1000mA?)
drive currents: 350 to 1000mA
relative intensity @690mA: ~175% (100% = intensity @350mA)
source: http://www.seoulsemicon.co.kr/_homepage/home_kor/product/spec/W42180.pdf


Am I missing something?


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## Christexan (Sep 25, 2007)

Doesn't look like you are missing much, except that the package measurements you are showing are not apples to apples, the Cree measurement that you list is only the metal ring surrounding the dome, not the whole package (7.0mmx9.0mm), the Rebel measurement is only the package width (3.17mm wide by 4.61mm tall at the most), and the SSC measurement you listed is the "flats" by the contacts (the actual package diameter excepting the flats is 8.0mm).
What are you trying to determine? Other considerations are the beam pattern of each, and the handling, and thermal, characteristics, the Cree is the best thermal package as far as allowing a large surface area, directly soldered thermal pad that is electrically isolated, the SSC is not electrically neutral which means isolation is needed (reducing the thermal effectiveness or requiring special design steps to prevent shorting), and the Rebel is just a pain to handle due to the tiny package size and limited thermal dissipation area (basically, if you can't get a good thermal path in a tiny area, it will hurt badly, unlike the Cree where you have around 36 sq mm (plus the electrical contacts add more heat dissipation) to get most of the heat out of even with a few voids here and there in the matrix). The Rebel has a roughly 5sq mm area for thermal dissipation, so a lot more critical to get a good consistent bond. In other words, a 1mm sq total void area in the Cree hurts to the tune of a 3% drop in thermal transfer, on a Rebel it would cost 20% of your thermal transfer. The SSC is also around 3sq-mm in area, so the same issues as the rebel, PLUS electrical isolation is a necessity, and it has about the same C/W as the Cree. 
Some have issues with the Cree electrical pads (designed for surface mounting, just like a Rebel), the vias can be ground off however removing that issue for top-wiring of the package, and then the entire bottom surface becomes a heatsink, for even better thermal transfer characteristics. 
The SSC P4 and Luxeon Rebel both have a similar wide lambertian light distribution pattern, the Cree is a much tighter pattern, so optics for the Cree won't work for the other two. The other 2 can use similar optics (or the same ones...) but may require compensation for different dome or board heights (shaving or elevating an optic/reflector to acquire proper focus). 
Hope that helps with the "missing" part?


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## mailint (Sep 25, 2007)

Christexan said:


> Doesn't look like you are missing much, except that the package measurements you are showing are not apples to apples, the Cree measurement that you list is only the metal ring surrounding the dome, not the whole package (7.0mmx9.0mm), the Rebel measurement is only the package width (3.17mm wide by 4.61mm tall at the most), and the SSC measurement you listed is the "flats" by the contacts (the actual package diameter excepting the flats is 8.0mm).
> What are you trying to determine? Other considerations are the beam pattern of each, and the handling, and thermal, characteristics, the Cree is the best thermal package as far as allowing a large surface area, directly soldered thermal pad that is electrically isolated, the SSC is not electrically neutral which means isolation is needed (reducing the thermal effectiveness or requiring special design steps to prevent shorting), and the Rebel is just a pain to handle due to the tiny package size and limited thermal dissipation area (basically, if you can't get a good thermal path in a tiny area, it will hurt badly, unlike the Cree where you have around 36 sq mm (plus the electrical contacts add more heat dissipation) to get most of the heat out of even with a few voids here and there in the matrix). The Rebel has a roughly 5sq mm area for thermal dissipation, so a lot more critical to get a good consistent bond. In other words, a 1mm sq total void area in the Cree hurts to the tune of a 3% drop in thermal transfer, on a Rebel it would cost 20% of your thermal transfer. The SSC is also around 3sq-mm in area, so the same issues as the rebel, PLUS electrical isolation is a necessity, and it has about the same C/W as the Cree.
> Some have issues with the Cree electrical pads (designed for surface mounting, just like a Rebel), the vias can be ground off however removing that issue for top-wiring of the package, and then the entire bottom surface becomes a heatsink, for even better thermal transfer characteristics.
> The SSC P4 and Luxeon Rebel both have a similar wide lambertian light distribution pattern, the Cree is a much tighter pattern, so optics for the Cree won't work for the other two. The other 2 can use similar optics (or the same ones...) but may require compensation for different dome or board heights (shaving or elevating an optic/reflector to acquire proper focus).
> Hope that helps with the "missing" part?


 
Thank you very much Christexan for all your very useful informations. I'm not expert like you but I'm trying to learn by reading much on this forum last days.

My project is this:

I own a 2xAAA 125mW green laser pointer that I love.
I always loved to have the best technologies in the minimum space in my pockets, always with me, for fun and for usefulness, so I'ld like to add an high-powered LED flashlight head/emitter on the other side of my laser pointer, soldering it on the metal back-cap of the laser (the cover of the batteries) and sharing the same batteries and the metal case of the laser, that will so become a little two heads monster 

My goal is to have short term brute force, i.e. the maximum LED brightness for some minutes, no matter the run-time nor if I can't leave it turned on for more than some minutes because of the heat problems, nor if I burn the LED once in a while.

My idea is to direct drive the LED with the lithium (or Li-ion? I saw that there AAA 3.7V Li-ion batteries on the market) batteries and to renounce to reflector and lens to save space and to conserve all the brightness. If the emission angle of the LED alone is <180° it's sufficient for me. Focus is not important for me.

Do you think that my project is realizable?

my main concerns are:
- what batteries can give the most brightness to the LED (while working alternatively for the laser, regulated or not) below their explosion point 
- if the metal case of the pointer will suffice to have at least the some minutes of LED brute force


PS: I just bought 2x Cree XR-E + 2x Luxeon Rebel + 2x SCC P4 on star/PCB and a computerized multimeter to learn their behaviour


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