02.02.2016, 00:27
Flat Screens Show Their True Colors
OREANDA-NEWS. Cathode ray tube television sets have long had their day. Flat screen TVs now provide energy-efficient, low-emission entertainment in three out of four German households, according to the Federal Statistical Office. And this figure is rising, Germans are estimated to have purchased eight million flat screen television sets in 2015, most of which are LCDs. LCD technology is also the basis for many other contemporary communication devices, including smartphones, laptops, and tablets. After all, with experts forecasting six percent global annual sales growth for flat-panel displays until 2020.
LCD stands for liquid crystal display. Liquid crystals form the basis for billions of flat-panel displays. The American, George H. Heilmeier, unveiled the first monochrome LCD monitor to the expert community in 1968. Commercialization of the first color monitors took another 20 years. Flat screen TVs started sweeping the world in the 1990s, mainly because of the availability of high-performance color filter materials.
The images on a liquid crystal display with the standard resolution are made up of about two million picture elements, better known as pixels.
The color filter pigments attached to the liquid crystal cells are what give each pixel its color. Screen contrast and color purity remain a challenge, however.
Red, green, and blue: Every pixel contains these three primary colors. The colors are composed of tiny crystals about a thousand times smaller in diameter than a human hair. The crystals act as a filter for the white backlight and only allow light waves from a selected range of the visible spectrum to pass through. These light waves show one of the three colors in its purest possible form. The filters block all the other wavelengths.
"A good pigment has a significant impact on the brilliance of the colors the viewer sees," said Dr. Hans Reichert, head of colorants research at BASF. "Although perfect color selection is not feasible with absorbing materials, we come fairly close to perfection with our red filters." Color purity also has an impact on the range of colors available. The greater the purity of the three primary colors, the more permutations that can be achieved by mixing them - and the more colorful the image.
The basic principle is simple. When the color red appears on the screen, the corresponding subpixel lets the red portion of light pass through and absorbs the rest. The other two subpixels - for blue and green - are deactivated when this happens. If, on the other hand, light penetrates through the red and green subpixel while the blue is deactivated, the colors combine to give a rich yellow. Fine-tuning the portions of the three primary colors in this manner produces millions of hues.
The liquid crystals fine-tune the blend of colors by twisting the plane of oscillation of the light waves. "This determines the brightness and color of the subpixels," said Ger de Keyzer, in charge of applications engineering for color filter materials at BASF. "The liquid crystals change direction, and in that way alter their optical properties depending on the voltage applied." They rotate the plane of oscillation of light waves to allow the light to pass through the second polarization filter. When an electrical field is applied, however, the crystals prevent some or all of the light from getting through.
To ensure that subpixels switch on and off the way they are supposed to, it is essential to prevent interferences from the color filter pigments. Any interferences resulting in scattering and depolarization of light will allow the light to pass uncontrolled through the filter. This contaminates the colors and compromises the contrast.
Tomorrow's television screens will have to meet even higher expectations in terms of resolution and color purity. In anticipation of the new demands, Lenz and his colleagues are taking their lab experiments one step further. Their aim is to find new materials that will show colors in an even more natural light.
LCD stands for liquid crystal display. Liquid crystals form the basis for billions of flat-panel displays. The American, George H. Heilmeier, unveiled the first monochrome LCD monitor to the expert community in 1968. Commercialization of the first color monitors took another 20 years. Flat screen TVs started sweeping the world in the 1990s, mainly because of the availability of high-performance color filter materials.
The images on a liquid crystal display with the standard resolution are made up of about two million picture elements, better known as pixels.
The color filter pigments attached to the liquid crystal cells are what give each pixel its color. Screen contrast and color purity remain a challenge, however.
Red, green, and blue: Every pixel contains these three primary colors. The colors are composed of tiny crystals about a thousand times smaller in diameter than a human hair. The crystals act as a filter for the white backlight and only allow light waves from a selected range of the visible spectrum to pass through. These light waves show one of the three colors in its purest possible form. The filters block all the other wavelengths.
"A good pigment has a significant impact on the brilliance of the colors the viewer sees," said Dr. Hans Reichert, head of colorants research at BASF. "Although perfect color selection is not feasible with absorbing materials, we come fairly close to perfection with our red filters." Color purity also has an impact on the range of colors available. The greater the purity of the three primary colors, the more permutations that can be achieved by mixing them - and the more colorful the image.
The basic principle is simple. When the color red appears on the screen, the corresponding subpixel lets the red portion of light pass through and absorbs the rest. The other two subpixels - for blue and green - are deactivated when this happens. If, on the other hand, light penetrates through the red and green subpixel while the blue is deactivated, the colors combine to give a rich yellow. Fine-tuning the portions of the three primary colors in this manner produces millions of hues.
The liquid crystals fine-tune the blend of colors by twisting the plane of oscillation of the light waves. "This determines the brightness and color of the subpixels," said Ger de Keyzer, in charge of applications engineering for color filter materials at BASF. "The liquid crystals change direction, and in that way alter their optical properties depending on the voltage applied." They rotate the plane of oscillation of light waves to allow the light to pass through the second polarization filter. When an electrical field is applied, however, the crystals prevent some or all of the light from getting through.
To ensure that subpixels switch on and off the way they are supposed to, it is essential to prevent interferences from the color filter pigments. Any interferences resulting in scattering and depolarization of light will allow the light to pass uncontrolled through the filter. This contaminates the colors and compromises the contrast.
Tomorrow's television screens will have to meet even higher expectations in terms of resolution and color purity. In anticipation of the new demands, Lenz and his colleagues are taking their lab experiments one step further. Their aim is to find new materials that will show colors in an even more natural light.
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