Forward voltage question...

I was looking at some old posts and noticed the TWOH luxeons are pretty rare and most consider these to be good as the VF is labeled as H bin. On the BIN code chart I see that there are several numbers lower than H bin yet I have never heard of any Luxeon lower than H for VF.
Can anyone tell me why there are no TWOG or even TWOF luxeons?...Is it simply a matter of psychics with luxeons not able to run below the H bin code?

What is it about certain Luxeons that determine the VF? Is it the thickness of the leads or the amount of coating on the actual die? I have always wondered if the VF is determined by lottery such as tint issues. Always wondered this however have never really asked.

The Vf is due to the materials, doping levels, and process variations. The first two can be controlled, the last can not. The materials determine the basic color range (blue/green vs amber/orange/red). The second determines the specific color within the range. The last determines how the Vf is binned.

Lumileds simply lists the possible ranges of Vf for the materials. G and F Vf bins are only listed simply because it's possible given the materials - but very unlikely to happen.

We get brightness, tint, and Vf variations in LEDs due to variations in the semiconductor manufacturing process. This is akin to why various CPUs are able to run at higher frequencies than others, or how some CPUs can run at a lower voltage and are able to be stuck into ultraportable laptops.

If Lumileds could, I'm sure every Lux I LED they produced would output 100 lumens, have a Vf of 2.8V, and perfect tint. Alas, manufacturing in the real world doesn't allow this to happen.

Another reason is that red LEDs run at a lower voltage than white (blue die) LEDs. I built a simple 2D Mag mod with a red Luxeon and a 1 ohm resistor. With 3 volts coming off the battery and the resistor dropping some of it, it would still overdrive the red LED at 475mA.
That leads me to believe it was a G bin but red LEDs tend to run at lower voltages anyway. I think I saw a 5mm red LED with a Vf of 2.2 volts a few years back.

Very interesting and thanks for the explanations. I am still wondering, with all the new advances,why this process can not be controlled.
So is it correct to assume that the manufacturer has no idea what tint or VF a Luxeon will be until it is finished?

Excellent source of all the latest news and developments in the LED world


http://www.ledsmagazine.com/

The manufacter can know the range based on the materials - for example, InGaN (indium-gallium-nitride) based LEDs (white, blue, green) will be in the 2.9-4.2V range, whereas AlInGaP (aluminium-indium-gallium-phosphide) based LEDs (red, orange, amber) will be in the 2.4-2.8V range. But as for an individual LED, yes, the exact Vf won't be known until it's finished.

Manufacturing tolerances on these devices have to do with the extremely advanced materials and processes that are being used. For example, a blue luxeon (which also is what a white luxeon is based on) has many layers of materials that are deposited with various techniques like chemical vapor deposition. Variances in the crystal lattice structure of the base materials, how well doping materials are deposited, thickness of layers, and impurities in materials all will affect various characteristics of an LED, including the Vf. The scale of manufacturing that we're talking about is sometimes on the order of a few molecules thick.

In addition, the materials handling/manufacturing processes are relatively young (remember, blue LEDs only came out in the mid-late 90s). There is a lot of advanced research happening to control all of the above stated factors - everyone is working very hard to correct for these manufacturing variances - it's in their best interest.

I've got a RX1G Luxeon that came in my Dorcy Metal Gear. I couldn't figure out why it was brighter than other Dorcy's until I took it apart and saw it had a G Vf. It's brighter because it's probably being overdriven, even with a resitor.

The RX1G (with the stock Dorcy resistor) is slightly brighter than a TWOK in direct drive with the same 3 NiMH cells.

1watt white G Vf! cool! thats equivilant to a LuxIII H Vf. A nice G Vf would be great in the Fenix light!

Nice to see that there are more R 1watt bins, and lower Vf bins showing up now. That means progress!