Green LED finally bright enough for large projectors

The Osram subsidiary Osram Opto Semiconductors, which is owned by Siemens Industry, is the only manufacturer to offer LED solutions for projectors in every performance class — from home cinema systems with an image diagonal of over 79 inches to tiny units that can be integrated directly into cell phones or MP4 players. Highly efficient lighting is part of the Siemens Environmental Portfolio, which generated around €28 billion in sales for the company in fiscal year 2010.

The brightness of an LED depends to a large extent on the output of the green LED, because green light accounts for more than two thirds of the white light produced in such projectors. The new diode emits 410 lumens of light at a wavelength of 520 nanometers, which is twice as bright as lamps used in the past. This means it is now possible to build systems of multiple LEDs that have a brightness of 2,000 lumens, enough for office projectors with image diagonals of up to several meters. The component is based on the latest chip technology for high-performance LEDs. Blue light is transformed into green light by means of phosphor converters. This allows the developers to achieve twice as much light as with directly generated green light.

Projectors superimpose images in the three primary colors red, green, and blue in rapid succession. Conventional devices use a special halogen lamp behind a rotating color wheel. LED projectors do without a color wheel because the diodes emit red, green, and blue light directly. What’s more, LEDs generate brilliant images with high contrast and high color saturation. They require less power and have a service life of about 30,000 hours, more than seven times as long as conventional lamps. In the past, however, LEDs have not been bright enough for office projectors, which have to supply about 2,000 lumens of light. The brightest pocket projectors now provide between 50 and 100 lumens.

Source: Siemens

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