Osram Opto announces side-emitting LEDs for portable display backlights

Osram Opto Semiconductors has announced new side-emitting LEDs in the MicroSideled 3806 family designed for backlighting screens in portable devices ranging from smartphones to tablets. The family includes a phosphor-converted white LED that enables LCDs to produce white images over a range of 2700K to 10,000K, and blue emitters intended for applications that use quantum dots.

The LEDs measure 3.8×1×0.6 mm. The low-profile LEDs are designed to optically couple directly to light guides in an edge-lit fashion and the planar light guides are placed behind an LCD to produce backlight. The LEDs are rated for 15,000 hours of life to L70, or 70% of their initial lumen output.

The white LED produces light in the 8000K CCT range. Osram said that the white point is a good match for the color filters typically used in LCDs and delivers optimum brightness and color gamut.

The white LED delivers efficacy of 150 lm/W and good uniformity in color and brightness. "For white, in particular, we offer very fine binning so there is always uniform color over the entire backlit surface," said MW Lui, product marketing manager at Osram Opto Semiconductors.

Blue LED and quantum dots

The blue LED is designed for use with quantum dot technology that is just coming to market in the display area. Quantum dots are excited by photons much like conventional phosphor, but the dots have a much narrower emission spectrum.

In a display application, the display manufacturer embeds red, green, and blue (RGB) quantum dots on a thin sheet of material that is placed between the light guide and the LCD. The dots are patterned to exactly match the LCD's RGB filters. Therefore, only red light is shone though red filters and the same scenario holds true for green and blue filters. The technology results in a display with richer colors and improved color gamut relative to LCDs backlit with white light.

The blue Osram LED would excite the quantum dots in a display application. Blue is chosen because LED manufacturers can deliver the best quantum efficiency with that color. Osram says that the blue MicroSideled 3806 delivers 55% external quantum efficiency.

Osram said that the blue LED and quantum dot technology will enable more efficient displays when the power consumption is considered at the system level. The quantum dots make more efficient use of the emitted photons because you don't have the situation, as with white light, where much of the spectral energy of the backlight is wasted when passing through the color filters. Osram said the advantage is 10–15% in energy consumption and 33% better coverage of the color space.