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A Revolution? The First Lumileds LCD Display

What Traditional LCD Offers

The principle of LCD displays is to put a light switch and a set of primary-color filters - red, green and blue, grouped together - in front of a source of white light. By controlling the degree to which each switch is opened or closed, the quantity of blue, red, and green is selected for each pixel, enabling a range of colors. Liquid crystals have the property of being able to rotate the plane of light polarization as a function of the voltage being applied to them; in LCD panels, the liquid crystal is what acts as the switch.

Unfortunately, there are faults inherent in the very qualities of LCD, and the backlighting used poses numerous problems. The light emitted by the fluorescent lamps used is not perfectly white, so manufacturers must sacrifice part of the range of opening and closing of the liquid crystal to make up for this imperfection. The phenomenon can also be compensated for through the choice of the color filters that are applied to the sub-pixels, but in doing so, part of the dynamic range of the pixel is lost.

Clearly, these issues limit the range of known colors for an LCD panel. Despite the efforts that have been made in this area in recent years, LCD panels can cover only the sRGB color space, and no more. That means that the color gamut of a monitor using traditional LCD technology looks like this:

That's not the only problem posed by backlighting; getting uniform lighting across the panel is also often difficult. That's especially so at the edges of the screen, and it is rare to find LCD displays that don't have a problem with halos of light around the edges or in the corners of the panel. What's more, fluorescent tube backlights have a limited lifespan, and the lamps can't be replaced. It's true that LCD displays often clock over 40,000 hours of operation, but increasing the power of the backlight reduces its longevity. And the panels used in big-screen LCD TV sets need high brightness since the viewer is sitting far from the panel.