Resistor for 4-LED Rotating Micro Beacon with Cool White LED Lights

I just purchased a 4-LED Rotating Micro Beacon with Cool White LED Lights and have already tested it.  It looks great!  I read that it is meant to be used at 5V, however in my application I will be running a circuit at 6V.  What size resistor should I put in series with the beacon?  Alternatively,  what is the LED voltage drop and maximum current rating?  With that, I could do the calculation myself.  Thanks in advance!