Acer aspirw 5100 brightness
1.The Function key (Fn), and the F6 key are pressed to turn the Backlight off to conserve power.
2.The Fn key and the right side arrow key, are pressed to increase Brightness.
You have a TFT LCD monitor screen. (Thin Film Transistor)
The LCD screen cannot be seen clearly without a Backlight.
The Backlight is a CCFL. Cold Cathode Fluorescent
tube. Resembles a small fluorescent tube used in residential, and commercial lighting.
The Backlight can go bad after time, and weaken.
If so, it will have to be replaced.
Sounds easy, it isn't.
The TFT LCD monitor screen is made up of layers. It's enclosed in a thin metal frame. Resembles a picture frame.
The frame is removed, after removing the LCD screen from the laptop's top cover.
The LCD screen transparent outside layers, are separated partially from the rest of the LCD screen.
The Backlight is removed out of the side.
This gives you an example of removing, and replacing an average Backlight,
Recommended job for a pro.