Backlights for Displays

Thomas Gottschau

Glass Tubing Improves the Lives of Monitors

High uv-blocked backlight tubes play an important role in flat screen monitors based on liquid crystals (LCDs). These components for use in backlighting extend the lifespans of lcd monitors quite considerably.

Regardless of whether they are designed for use in televisions, laptops, navigation systems or cell phones, thanks to their thin depth of construction, flat TFT-LCDs (Thin Film Transistor-Liquid Crystal Displays) are gaining ground in nearly all visual electronic applications. However, unlike cathode ray tube systems, these types of flat screen monitors require a background lighting source in order to be able to display an image on the screen. Cold cathode fluorescent lamps (CCFL), also referred to as backlights, that essentially function much like miniaturized neon tubes, perform this task. And just like their larger counterparts, they have a weakness. During operation, CCFL (Cold Cathode Fluorescent Lamps) backlights generate UVB and UVC radiation. Over time, this can damage important components inside the monitors. The LGP (Light Guide Plate) located behind the TFT (Thin Film Transition) is primarily made of plastic and reacts quite sensitively. This component is responsible for uniform illumination, brilliance of color and brightness. UV radiation causes the components to turn yellow and, thus, impairs the image quality, brightness and color values.

Breakthrough with new glasses

Whereas backlights made of conventional glasses are capable of absorbing UV radiation, there was no solution for UVB radiation, until only recently. As one of the world’s leading manufacturers of special glass, SCHOTT accepted the challenge. “In October of 2002, our research and development teams in Germany at both our manufacturing site for special glass tubing in Mitterteich and our headquarters in Mainz started to perform initial testing aimed at developing new types of glasses that would be capable of blocking both UVC and UVB radiation,” explains Dr. Brigitte Hueber, head of technical and scientific customer consulting at SCHOTT-Rohrglas. The challenges were immense. “During our initial testing, the glass either experienced discoloration or became cloudy when it was subjected to higher temperatures,” Dr. Franz Ott, Head of Development of Smelting and Drawing Techniques at SCHOTT-Rohrglas, remembers. The research team quickly realized that impurities in the glass were causing the discoloration. By optimizing the glass recipe, they were able to eliminate these, however. In fact, as a result of its research work, SCHOTT was successful in presenting its new types of glass, 8688 (Tungsten type) and 8271 (Kovar type), back in 2003. They differ with respect to the fact that 8688 Tungsten type can be bonded together with electrodes made of Wolfram, whereas 8271 Kovar type calls for metallic Kovar alloys.

Despite the sober sounding abbreviations, what really stands behind them is a breakthrough in the area of high UVB- and UVC-blocked backlight tubes that doubles the average life span of TFT-LCDs to up to ten years. “These products have enabled us to assume a strong position inside the global market, due to the fact that hardly anyone else is capable of manufacturing glasses with comparable specific characteristics,” emphasizes Dr. Hueber. Glass tubes from SCHOTT meet even the most challenging demands with respect to life span, dimensional accuracy, residual stress and straightness. From a customer perspective, this last trait, in particular, means that processing can be completed cost-effectively. “With a length of 600 millimeters, the curvature of our tubes is only 0.2 millimeters. This means that no retroactive straightening of the glasses is necessary,” explains Wolfgang Zettl, head of production.