5W power led datasheet
Here is a 5W power led datasheet. I have several questions about it :


Hmmm don't like that datasheet much.


  What does "Peak Current (1 / 10 Duty Cycle, 0.1ms Pulse Width) - 1000mA" mean?


It means that each die, of which there are four total in 2s2p arrangement, can withstand 1A of current so long as it is at no more than a 10% duty cycle and pulses no longer than 0.1ms.  The full LED package has 2 parallel lines of dies, so for the whole package, this would be 2A at no more than 10% duty and pulses shorter than 0.1ms.


  Does that mean 1000 mA peak current is possible IF maximum ON time is 0.1ms AND duty cycle = 1/10 corresponding to a driving signal F = 1KHz? 


Shorter pulses or lower than 10% duty cycle is fine and again this is per die.


  If F decreases, e.g. 500Hz, limiting condition is "0.1ms Pulse Width" : max duty cycle will be 1/20. If F increases e.g. 2kHz, limiting condition is "1 / 10 Duty Cycle" max pulse width will be 50µs.


Yeppers!


  After in electrical and optical characteristics, Why are values given for If = 1050mA > If(Peak)?


Keep in mind the absolute maximum 1A is for a single die and the absolute maximum for the 2p array is 2A.  The ratings in the Electrical and optical characteristics appear to be for the whole package, and they give brightness, and expected forward voltage Vf based on a 1050mA current across all dies.  Note that this test value appears to exceed(1.05A*6.5V=6.825W) the 5W continuous rating of the LED package, and that at this current the LED only produces 400lm/6.825W=58 lumen/watt. 


  What are Rank L1/L2, Rank V1/V2?


Binning numbers that appear somewhere in the manufacturer product/serial number and indicate specific qualities about the LED, in this case, the brightness and forward voltage it has at 1050mA.  Further down the datasheet there are more bins for chromaticity.


  During short duration pulses LED power dissipation is 6.5 x 1050 = 6.8W, giving 680mW with 1/10 duty cycle. In continuous mode Vf ~ 5.5V @350mA giving a 1.9W dissipated power. So why is this product named 5W LED?


Just note that because it's running through 2 sets of dies in parallel, the 1050mA current is only 525mA per die when you compare against the rows of the first table with asterixes, so if you're evaluating absolute maximum duty cycle or pulse width, 1050mA over the whole package is only half of the absolute maximum current.

If you adjust the voltage/current to actually run the LED at 5W, you will likely see an efficiency improvement, which is good because 58lm/W is pretty bad.  Why they've chosen to write their datasheet this way, I don't know.