I don't mean to offend anyone but you all seem to have missed the blatantly obvious and that is the LED backlight array. LEDs age, and as such the amount of light that is emitted reduces. The LEDS in the LM240WU6 panel are made by Lumileds which is a subsidiary of Philips who in turn produced the panel under license from LG. The LEDs used are LXML-PWN1-0120 which should be operated at a forward voltage of between 3.0V & 3.6V @ 350mA and have a stated 39000 hours of life. LEDs operate in constant current mode that is the current through the device is adjusted by altering the voltage across it. In low current LED applications this done with a simple resister. In high powered applications this is done with a controller chip such as the HV9982. Most high powered applications work as a closed loop system, that is they monitor the current flowing in the LED string and adjust the voltage across the string accordingly. The circuit Apple adopted does just that, it monitors the voltage developed across a low ohm...