If LCD and LED monitors look similar, that's because they are. Both LCD and LED use the same basic display technology. The difference between the two is only how the display is illuminated.
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LCD displays are not self-illuminating. They need a backlight in order to produce a visible picture. Regular LCDs are backlit by CCFLs (Cold Cathode Florescent Lamps). These lights resemble the florescent light tubes used for lighting, and are arranged in horizontal rows behind the LCD screen.
An LED TV still uses an LCD display, but instead of CCFLs, it is illuminated using an array of LED lights. Other than that, an LED display is nearly identical to an LCD one, though LED is the newer, more contemporary feature.
Since LED lights are smaller and thinner than CCFLs, an LED monitor can be thinner and more lightweight than an LCD monitor that uses CCFLs. LED lights are also more energy efficient than CCFL lights, and perform better as well. According to NY Times writer Eric A. Taub, this is because CCFL lights always have to be on, which hurts contrast levels in darker scenes. LED lights are only illuminating when they need to be, so contrast and black levels on an LED monitor are usually superior to those found on an LCD display that uses CCFL lights.