How can I recognize LEDs

[MikePL]

Threre are many different kinds of LEDs and I am confused because there are many sellers, for example on Ebay, who don't give detailed descriptions. Is there a way to distinguish LEDs basing only on their looks?

I have this LED and don't know anything about it. There's nothing on it except for a 'Lumileds' text, as you can see. And there are lots of LEDs of this type, and sellers write 'I have a 3W white LED for sale' and nothing more. Any help would be appreciated.

 

[kanarie]

look it up in the spec. sheet from the manuf. and compare form and dimensions. (I think this is a lumiled luxeon)
There is no other way because based on the outside most of the time you also don't have a clue of the color/bin
It is best to buy from a CPF trusted dealer if you want to know what you buy

 

[LukeA]

If it's just a wattage rating given, it's most likely a luxeon.

 

[MikePL]

Thanks a lot for your answers. Sometimes the most obvious things do not come to mind, such as 'go and look at datasheets'. Yup, the above LED looks like a Luxeon III. I have two questions, however...

QUESTION 1.
Are there fake LEDs around. I mean no name companies that produce them and sell as brand LEDs. I ask because many of the LEDs I have do not make full contact with the star board. In my opinion they should, as this is their heatsink, but they don't. So I started to wonder if I have genuine Luxeons or fake ones.

QUESTION 2.
I have visited the Kaidomain website but I find it difficult to get LED drivers that suit my purpose. I wish to power the LEDs at 750mA (or maybe 1000mA pulse) and power it from 12V (interior lights in car). Could anyone point me to the right LED driver for the purpose?

12-14.5V input
700mA output (or 1000mA for PWM)
protection against EM spikes and all that car related stuff

Bib big thanks

 

[Gryloc]

MikePL,

I just wanted to mention really quick that there are a bunch of clones that are made in China. Some are pretty decent and they can be hard to tell apart from an authentic Luxeon, but sometimes you get junk. I wish there was a way to tell them apart sometimes. Nowadays, seeing how Cree XR-Es are tossed in many cheap Chinese lights, you might actually have an authentic emitter. I thought that Cree XR-Es are tough to copy, so manufacturers just buy up a giant lot and attach them to their cheap generic stars. Could they be doing the same with the Luxeon IIIs nowadays? Besides, I thought that Lumileds are doing a lot of legal stuff with patent infringements, so there could be less clones used. Maybe not. I am not a pro with this matter, but this is what I am guessing/assuming by how products are being sold nowadays.

As for drivers. I wish I could help you there. It is so difficult to find automotive LED drivers. There are quite a few around that power a single Luxeon III at 700mA to 1000mA, but if you want to power three or four in series (which is always nice to do), it is more difficult. I am working with LED forward lighting and I may have to build my own. I require powering the LEDs at full power even with the engine not running (needing the voltage to be boosted some), though.

Anyway, you will find something. As for protection against spikes and stuff (it can be some nasty stuff), I can help you find a few components that will protect you with that. I do not think that any driver boards sold yet includes protection circuitry. All you need is Transient Voltage Suppressor (TVS) diode and a capacitor. The TVS diode, when hooked in parallel to your circuit (in the right polarity), absorbs any current that rushes in at a voltage over its specs (its breakdown voltage). For example, I bought a few rated for 16V. If a quick 42V pulse at 10A would rush through the wiring when my starter motor quickly turned off, the TVS diode would clamp, therefore shorting out the circuit through the TVS diode, and absorbing the entire pulse. The TVS will dissipate this energy as heat, and the LED driver is safer now. For dirty power that still passes through, the capacitor will smooth out the voltage some. Extremely quick pulses may pass through and damage the circuit, but oh well. I can help you pick protection components that will help, just PM me. Good luck!

-Tony

 

[Lightingguy321]

For drivers for those LEDs try the Buck Puck or Boost Puck, both are great little premade driver circuits, all you have to do is connect a source power supply and the other end to the LEDs. As for weather or not the Lux IIIs you got are real or not, is there a product/Binning code on the bottom of the Star Shaped PCB. By the looks of it, it looks pretty much like an authentic Lux III star, just check for the info. If no info is present, then it is most likely a fake.

 

[Illum]

if its a lumiled
it must have

1. a bin code in the back of the star
2. the star is rice colored, not white
3. "lumileds" is written clearly on pcb, not drawn out by solder
4. the pcb's electrical contacts are predripped with a small amount of solder, while clones have usually flat contacts
5. the emitter is thermally epoxied to the star [compared to only being "thermally greased" to the star like Seouls are]

your star is a clone, it probably wont function for too long at 3W, but who knows

 

[Gunner12]

Just search in the DIY section of Dealextreme and Kaidomain and you could see how many LEDs look. Cree XR-E Q5 LED(all XR-E LEDs look like this, minus the star board), Bare Cree XR-E Q5 LED, Seoul P4 Star, Seoul P4 Bare, Rebel Star, Board, Bare(in packing), Luxeon I, III, K2, all bare. The Rebel, Cree, and Seoul are the more efficient ones.

This driver will take up to 18v but I don't know how it will handle spikes.

The LED in you picture is probably a Luxeon or a copy.

 

[Mark620]

It looks like it has been removed from the board....

 

[MikePL]

Thanks a lot for all the information. It turned into a very informative thread... Very well.

Gunner12, are you sure the driver you mentioned will be good for my purpose? I was also looking at it but I have some doubts.

At the beginning of the description there is such a sentence:

Total input voltage must be 1-3V higher than output voltage,

Does it mean that I have to constrain myself within 1 or 3 volts or is it given as a minimum?

When I connect this driver to 12V and the LED has a voltage rating of 3.5V, then the difference between input and output will be 8.5V.

It's good that I can connect up to 5 LEDs to this driver but I also have places where I will be able to connect only one LED. Can it be done with this driver.

Or maybe I am simply mis-understanding the description and there is no problem in connecting one LED to the driver and the driver to 12V?

 

[SemiMan]

I would suggest following Greyloc's recommendations for drivers. Automotive environments have something called load dump that can be as high as 40 or 60 volts depend on your vehicle manufacturer. It will eat regulators pretty quickly if they are not designed for it. It is easy to handle as Greyloc has pointed out.

It is pretty easy to pick a newer, real Luxeon. They use what is called a conformal phosphor process. The phosphor will appear to only cover the die and not the whole inside of the package. The only one else who seems to do that currently is OSRAM who I think may have licensed the process and I have only seen that on the OSTAR multiple die parts.

Someone else pointed out that Lumileds stars have Lumileds in writing, not in copper on the PCB. That is not to say that Lumiled is the only ony that can make a good star. It is not that hard (but not cheap) to make a better one. Seouls are a little harder to tell, except electrically they are reversed usually from Luxeons and most clones are based on Luxeon. Crees XRs do not appear to have been copied yet, but give it time. For Cree and Seoul there are lots of stars of a wide range of quality. Best idea is to ask on here for what works. Someone is likely to have tried it.

Semiman

 

[Lyndon]

The bottom line to your Q1 is that if "fake" really matters to you, then you have to get the actual real manufacturer you want, probably from a recognized distributor. In most cases it shouldn't make a difference, but if there are critical items on a datasheet that your product requires, then you gotta get the real thing.

As far as contact with the heatsink, I wouldn't worry too much. The most direct contact with the die is going to be through the power leads. If there's low thermal resistance between those leads and the heatsink, then you're fine. I'm prototyping a light with a blue LED and a brass fixture and my thought right now is to solder the anode or cathode directly to the brass to dissipate heat.

Thanks a lot for your answers. Sometimes the most obvious things do not come to mind, such as 'go and look at datasheets'. Yup, the above LED looks like a Luxeon III. I have two questions, however...

QUESTION 1.
Are there fake LEDs around. I mean no name companies that produce them and sell as brand LEDs. I ask because many of the LEDs I have do not make full contact with the star board. In my opinion they should, as this is their heatsink, but they don't. So I started to wonder if I have genuine Luxeons or fake ones.

QUESTION 2.
I have visited the Kaidomain website but I find it difficult to get LED drivers that suit my purpose. I wish to power the LEDs at 750mA (or maybe 1000mA pulse) and power it from 12V (interior lights in car). Could anyone point me to the right LED driver for the purpose?

12-14.5V input
700mA output (or 1000mA for PWM)
protection against EM spikes and all that car related stuff

Bib big thanks

 

[Lightingguy321]

On second thought, and glance, that LED is definetly a fake Lux III, it lacks all of the characteristics of a real Luxeon Star and even though I don't have that specific LED in front of me, my guess is that there isn't a cat code or bin code on the under side of the star. Also notice that it looks like the Anode lead of the LED is almost skidding off of the Star shaped PCB, this means the LED was not soldered correctly. The leads that are coming out of the LED are also lacking the lumileds gullwing configuration pattern. The configuration of a gullwing has both leads when coming out of the package take a 90° bend and run vertically (parrellel to each other) and then another 90° bend and the two primary solder points of the leads should land on the solder pad. Your LED appears to have both lead wires curved and angled into the PCB solder pads before soldering. All lumileds stars use a luxeon emitter mounted on a PCB that is shaped so that the solder pads are just slightly larger than the leads on the Luxeon emitter, how ever, in your case, the LED doesn't even have the lumileds gullwing lead configuration from the start and was just simply curved into shape to sit onto the PCB, which explains why the anode contact of the LED is slightly slide off of the anode's solder pad. Also the hole in the lead frame of a luxeon dictates the anode (+) side of the LED, not the cathode, which means your LED is definetly a clone. The polarity on your LED appears to be reversed. Also notice the non uniform solder coating over the anode side of the LED, with a genuine lumileds Luxeon star, the pad and the LED are very uniformly covered with solder such that the solder joint looks like a shiny fillet (sometimes slightly dull) and the solder coating on a real luxeon star doesn't allow you to partially see the contact lead of the LED. Last but not least, the LED is ever so slightly of center on the PCB which kind of gives away that it is not a luxeon star, since most lumileds made stars have the LEDS near perfectly centered on the PCB.

 

[Calina]

It could very well be that you have a genuine Lumiled mounted on a star of unknown origin.

 

[Tritium]

As far as contact with the heatsink, I wouldn't worry too much. The most direct contact with the die is going to be through the power leads.

Alright, that statement is Incorrect :shakehead for power led packages. The slug is where the heat is dissipated NOT the leads that are attached with "thin" gold wires". The slug must be in good contact with a heat sink.

Thurmond

 

[Gunner12]

If the driver can take spikes(I'm guessing it can take small spikes but not big ones), then It would work.

Quote form site,

- Case 1: Use one CREE XR-E LED that consumes VF: 3.5V and 750mA with four 18650 battery. The input voltage will be around 12V, with the input current is about 200mA. (10 hours runtime on current regulated 750mA)

So it should work even with a 8.5v difference between Vin and Vout.

 

[Lightingguy321]

As of now (unless this LED is a clone) I have never ran into a lumileds Luxeon Star of any rating that has curved out leads, all of the Luxs I own (including lux III) have gull wing style leads, not curved out ones. So I think the fact that more than half of the physically noticeable differences on this led single it out as a clone.

 

[MikePL]

I see that this thread has generated some attention so I've decided to post some more pics. Now I am sure that these LEDs are clones. There are no numbers on the back of the star. Personally I am not touched by this because these LEDs stand up to their task and I am satisfied with their output, but others beware.

 

[legtu]

ouch... if you have more than one of these LEDs, i'd suggest checking or desoldering all of them from the star, place a thin layer of thermal compound and make sure that the LED is making good contact with the star.

this pict clearly shows that majority of the base of the LED is just hanging in the air and that will cause it to degrade quickly, especially at higher currents.

 

[Lightingguy321]

Definetly a clone then