Figuring/setting BJT mode of operation
You are using the wrong topology for what you are trying to achieve.  Here is a better circuit:



First, we figure out R2.  This is what sets the LED current.  You want 700 mA.  D1 drops 1.4 V, and let's say the transistor saturates to 300 mV.  That leaves 3.3 V across the resistor.  (3.3 V)/(700 mA) = 4.7 &Omega;.  Note that this resistor will dissipate (3.3 V)(700 mA) = 2.3 W.

Now for the base resistor.  You need 700 mA collector current, so you need at least that divided by the transistor gain as base current.  Let's say the minimum guaranteed gain of the transistor at 700 mA is 50.  (700 mA)/50 = 14 mA minimum required base current.  Figure the B-E drop will be 750 mV, so that leaves 4.25 V across R1.  (4.25 V)/(14 mA) = 304 &Omega;.  So the largest common value that guarantees everything within spec is 270 &Omega;.