The difference between LCD and LED televisions is the lighting technology used. Both LCDs and LEDs use a liquid crystal matrix to display images, but LCDs use a fluorescent panel as a backlight, while LEDs use an array of LED bulbs.
The fluorescent panels used in LCD screens are cheaper than LED arrays, but they are more bulky, use more energy and produce more heat. They also provide uniform light levels across the entire screen, requiring the liquid crystal matrix to go opaque in order to produce blacks and dark colors. LED bulbs in arrays can be lit independently of one another, allowing for greater control over light and color intensity levels.