If you have used LCDs in projects before you have realized that to use the backlight on a LCD display you need large positive and negative voltages.
This circuit will help you create the voltages you need from a simple 2.5V to 6V input. I chose this circuit since many of my projects run off of two AA batteries. The one IC in this circuit, LT3587, generates two positive and one negative high voltage supply.
For more detail: LCD Display Backlight Power Supply Circuit