Siemens green LED provides more lumens for LED projectors

Projectors in conference rooms have to be very bright for viewers to easily see the large images even in daylight. So far, light-emitting diode (LED) light sources have been used primarily in pocket projectors, cell phones, or home cinema systems, but the folks from Osram Opto Semiconductors came up with an extremely bright, green LED that makes LED projectors in office environments possible.

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.

Conventional projectors use a special halogen lamp behind a rotating color wheel in order to superimpose images in the three primary colors (red, green, and blue) in rapid succession. LED projectors function without a color wheel because the diodes emit red, green, and blue light directly. LEDs are able to generate brilliant images with high contrast and high color saturation, while they require less power and have a service life of about 30,000 hours (more than seven times as long as conventional lamps).

However, previous LEDs have not been bright enough to serve as office projectors, which have to supply about 2,000 lumens of light (in comparison, the brightest pocket projectors now provide between 50 and 100 lumens).

The brightness of an LED projector 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. The new diode also has a very uniform luminous area.

Beginning in mid-2011 it will be used to open up the office projector market, while the first components are already being delivered to customers.