Here is another table showing LED Voltages.
The voltage across a LED depends on the manufacturer, the intensity of the color and the actual color.
LED VOLTAGES depend on many factors.
You must test the LED(s) you are using.
The voltage across some LEDs increases by 500mV (0.5v) when the current increases from about 10mA to 25-30mA and if you have 6 LEDs in series, this is an increase of 3v.
If you are using a 12v supply, you will need to remove one LED to get the brightness you require.