A current mirror is a simple, high-impedance input current control. If you set the base voltage with a divider through one diode-connected transistor, its base can be used to control the emitter voltage of other bipolars. IF you set the cathode current of your LED's with a current mirror, it will remain quite constant, and pretty well-controlled. Look up current mirror on the WWW http://en.wikipedia.org/wiki/Curr...oximations. You'll see...

If rather than connecting the emitter to GND, you insert an emitter resistor, that resistor will control the current. Since the base voltage is well controlled through the mirror, the load at the collector has little effect on the current flowing through the emitter. Consequently, you can use an arbitrarily high (within reasonable limits, of course) voltage at the supply and simply switch the anode current on and off as needed. Vf of your LED will have no impact as a result.

You should, however, consider the power in the resistors and ensure they are adequate.

RE