Digging Into LED Backlight of New Bravia TV

Jan 26, 2010 10:21 Satoshi Okubo, Nikkei Electronics

Sony Corp unveiled the structure of the LED backlight of its new Bravia LCD TVs, the EX700 series, Jan 20, 2010.

The backlight consists of three diffuser panels, a light guide plate and a reflector plate (from the back side of the LCD panel). And LEDs are positioned at the top and bottom edges of the light guide plate as light sources (See related article). Compared with the ZX5 series LED-backlit LCD TVs, which were announced in 2009, Sony improved the positions of the light sources and the shape of the light guide plate this time.

In regard to light sources, while the ZX5 has LEDs lined up only at the bottom edge of its light guide plate, the LEDs of the EX700 are positioned at the top and bottom edges of the plate. Though the details of the white LEDs lined up in the ZX5 have not been disclosed, the EX700 has a larger number of LEDs with a smaller optical output.

The cost of each white LED employed this time is lower than the one used for the ZX5, lowering the total cost of the LCD TV regardless of the increased number of LEDs.

Sony did not disclose the number of white LEDs used for the EX700, but we estimated it from a cut model of the 40-inch model's backlight. Streams of light were emitted from the exposed light source (white LEDs) of the cut model. Judging by the number of the streams, we estimated that about 100 LEDs are used at each of the top and bottom edges of the panel.

Also, the power being consumed by the cut model was displayed. When all of the power (about 80W) is used for the white LEDs, each LED consumes a power of about 0.4W, which is equivalent to the power consumption of a white LED with a medium output.

As for the light guide plate, Sony ensured enough brightness and enhanced the uniformity of brightness by improving the mesh structure formed on the surface of the plate and optimizing the size and the pitch of the apertural area.

The light emitted from the white LEDs, after entering the light guide plate, (1) goes out of the mesh-structured apertural area or (2) is reflected between the non-aperture area and the reflector plate and goes through the light guide plate.

The closer to the light source an aperture is, the smaller the size of the aperture becomes. In other words, the size of an aperture is larger near the center of the light guide plate. The amount of light going out of the light guide plate is smaller near the light sources, and it becomes larger at the center of the plate.

24 Hours | 7 Days