Hum.. "LED Forward Voltage" means the voltage it needs to work, right?
Not exactly. It won't work when supplied with less than that amount of voltage, but you cannot connect the LED to a supply that is equal to the LED forward voltage and expect it to survive for long.
The LED forward voltage is the voltage that will appear across the LED when it is operating at it's rated current. You typically start out with a supply voltage greater than the LED forward voltage and choose a series resistor to limit the current to the rated value.
Example: A typical red LED has a forward voltage of 1.7v at 20 mA. If it is operating from a 5v supply then 3.3 v (5 - 1.7) will be dropped across the series resistor. For this to happen the resistor must be 165 ohms. You would use the next higher standard resistance which is 180 ohms.
The calculation for the backlight isn't this simple. The LEDs aren't red so the forward voltage is different. There are typically several LEDs in series so Vf is not 1.7v, and there are typically several parallel groups of LEDs so the required current isn't 20 mA.
If you want to experiment with a variable resistor then make sure you also use a fixed resistor in series with it so you don't burn it out as Mike was mentioning.