PRODUCT DESIGN - LED ARRAY

Array and Typology

Reliability

As a solid state device, LED’s are reliable and robust which makes them ideal for display applications

Efficiency

At the same brightness, LCD TVs using LEDs with local dimming can save up to 30% power consumption on average versus CCFL-based while viewing typical video content LEDs power efficiency doubles every 18 months (Haitz’s Law)

Fast

LEDs have a much faster response time than a typical LCD panel. This advantage allows LEDs to be turned completely off on a frame-to-frame basis to produce true blacks and high static contrast ratios.

Uniformity

Even if as LED’s age, they tend to lose their luminance output at different rates, thanks to SIM2’s calibration solutions LEDs can easily recover luminance through adjusting their drive current instead of using tightly binned LEDs (cost-adder).

SIM2 Factory Calibration:

SIM2 has developed processes to assure that a display will have good uniformity when it leaves the factory production line using algorithms and a CCD camera.

SIM2 Lifetime Calibration:

SIM2, thanks to sporadic use of autocalibration software and dedicated processes, has been able to assure that a display will retain its uniformity throughout its product lifetime.

Coupling and Reflectors

Introduction

The HDR display has an active matrix of LEDs behind the LCD optical stack. This matrix of LEDs is effectively a low-resolution image that can be modulated in series with the LCD panel. The contrast of this LED image multiplies with the contrast of the LCD image which increases the dynamic range of the display. In other words, one way to maximize the contrast of the display is to maximize the contrast of the LED image.
This means that light leakage from one LED to adjacent areas must be minimized. Light leakage to adjacent areas is primarily due to reflections from the optical stack. This is best illustrated by the simplified 2-D schematic shown in Figure 1 on the right.

LED Reflectors

The method chosen by SIM2 in order to minimize the light leaking from one LED to its adjacent areas and maximizing the contrast of the LED image is to introduce a reflector around the LED which spatially restricts the light from one LED to within a specified area surrounding the LED. An example of such an LED reflector is illustrated by the simple 2-D schematic shown in Figure 2 below. Fig.2 LED reflector schematic

The top shape of the reflector is very important because of the fact that any flat areas at the top of the reflector will correspond to a dark shadow through the LCD screen.

For example, for hexagonally packed LEDs, a reflector with a hexagonal top shape is required such that there are no flat areas at the top of the reflector array, as illustrated in Figure 3 below. If a reflector with a round top shape was used in conjunction with hexagonally packed LEDs, then “dead” packing areas would be introduced.

On the opposite, the bottom has to be shaped to fit the emission area of the LED in order to maximize reflectance. If the area of the bottom did not fit the emission area, one would essentially have a lower level of reflection at the bottom and those areas would translate into observably darker spots through the LCD. As well, the bottom of the reflector should be as flush as possible to or slightly lower than the emission plane in order to ensure that light was not trapped below the reflector.