In most LCD monitors the backlights are like small flourescent tubes.
They run on a ballast supply. Generally the supply, and or the lamps
fail. When servicing these, it is good practice to change both the
supply and the lamps together.

There is a new type of LCD monitor that is using an LED backlighting
system. This ia a much more expensive setup at this time.

In a year or two, the LED displays are supposed to come out. The screen
will be LED based rather than LCD based. This sreen will have no need
for back lighting.

Jerry G.