It's a bit complicated to find out the lumen output from an LED. You need to know the brightness in millicandela (mcd) and the beam angle, then you can use this calculator:
http://led.linear1.org/lumen.wizBut simply, any LED running off 20 milliAmps is going to be ok, and more will be brighter, but you really just have to try it. (Any LED running off more than that will be bright, but will require lots of special circuitry to run it.) The Mitochondrion glowstaff runs off forty 20 mA LEDs, and that's plenty bright for most uses.