Ref 4 by DigitalView is a good read, tells many advanced things including how to use a sensor to check ambient light and adjust brightness and back light accordingly. Ref 5 by Lady Ada is also good, saying that they actually designed their LCD module that can control backlit in two ways: 
(a) PWM Backlight Control with GPIO 18

(b) [AdaFruit] designed the board with the STMPE610 touchscreen controller which has 2 extra GPIO and tied one of them to control the backlight. You can use the command line to control the backlight.