The "bin" an LED is labeled with is a way for the manufacturer to indicate slight variations between the parts that fall under a given model name.
So, Cree produces an LED called "Royal Blue XR-E" but not all royal blue XR-E are identical - they vary from chip to chip. In order to allow customers to pick the individual parts that best meet their needs, Cree "bins" the LEDs by sorting them according to variances in important parameters.
For most of their LEDs, they label each batch with a brightness bin and a color bin. This indicates the relative brightness and color of a particular LED against all other LEDs with the same model name.
Here is the binning and labeling guide for the XR-E LEDs:
http://www.cree.com/products/pdf/XLamp7090XR-E_B&L.pdf
If you look at page 4, it shows the brightness bins for the Royal Blue XR-E. Each bin is given a range of radiant flux (brightness) at a stated test current (350mA):
bin min max
12 250 300
13 300 350
14 350 425
15 425 500
16 500 600
So, you know that if you get brightness bin 15, your royal blue LEDs will produce between 425 and 500 radiant flux per watt consumed. If you get brightness bin 16, you'll get between 500 and 600 radiant flux per watt. In other words, if you choose bin 16 instead of bin 15, it's like
extra light, totally free of charge because the LED is simply producing more output per watt it consumes.
The other way that Cree bins LEDs is by color. For Royal Blue, they bin according to dominant wavelength and specify a minimum and maximum wavelength as follows:
bin min max
D3 450 455
D4 455 460
D5 460 465
So, again, you have some choice. If you want a deeper, more purple glow, use the D3 bin. If you want something a little bluer, use the D5 bin. The differences will be small but you have the choice.
This concept is foreign to people who have a background with traditional reef lighting (MH and T5) because with those technologies, you typically don't get anywhere near this level of information and choice. But, for LEDs, at least the brightness bin is critically important to understand. The 15 bin LEDsupply sells isn't the end of the world, but if you take things to extreme, two LEDs given the same model number can have VASTLY different outputs. For instance, a bin 12 Royal Blue LED will put out exactly half the light as a bin 16, despite both being the same "product" in terms of model number.
Unless you're using a really small number of LEDs on a small tank, the patterns will all overlap enough that you won't be able to tell the difference.
