Illuminating LEDs for Projection

LEDs have long been considered a promising but technically challenging prospective light source for front projection displays. Indeed, LED illuminated rear screen televisions hit the consumer market a few years ago and their performance benefits were impressive: instant on, tens of thousands of hours of operational life, the production of a broader and more stable color space than traditional lamp technologies and efficient lumen-per-watt performance. The question has always been whether an LED illumination system could be bright enough to support front projection applications.

In a back corner of our exhibit at CEDIA, DP demonstrated our prototype LED illuminated single-chip projector. It is based on a bold LED concept known as Phlatlight™. More of a tightly spaced, tiny array of LEDs then a single really bright LED, the R, G and B Phlatlight™’s employed in our prototype are capable of producing thousands of raw lumens with just 360 watts of maximum illumination power. Even more interesting, the switching time of the LEDs is so fast they not only replace the traditional lamp system – they also remove the need for the motor driven color wheel, previously required by all single chip projectors. Removal of the color wheel also means removal of color wheel artifacts. For anyone sensitive to the color-wheel induced rainbow effect, eliminating that visual artifact is a huge, if not revolutionary, benefit.

Also, because the LEDs can be turned all the way off, implementations of these systems with dynamic black will be able to match CRT black levels on full-field black scenes.

Reproducible color gamut is another interesting benefit of LED illumination systems. Because the color point of the red, green and blue LEDs can be defined so precisely, they enable single-chip projectors to produce a color space and color saturation far beyond that of color-wheel based single-chip projectors (but still not on par with 3-chip systems).

With such a compelling set of benefits, one might be convinced that LED illumination is the optimum solution for every application. The barrier to that concept, and the primary reason LED illumination will have very clear limits for front and large screen rear projection applications, is total system lumen output. Our prototype produced 480 ANSI lumens on screen. While we can envision the light output increasing to 700 – 800 lumens by the time the first LED illuminated projectors are launched (late 2009), brightness gains beyond that threshold are likely to be limited and slow to emerge.

By comparison, DP offers single and dual color wheel-based single chip projectors producing 6000+ lumens today. Even our entry-level single-chip projectors produce 1500+ lumens. Of course, our three chip systems can deliver up to tens of thousands of lumens and color depth beyond any single chip solution – color wheel or LED based.

That is where we get back to the question of the future LED illuminated single-chip projector’s suitability for specific applications. When using a small to medium sized screen in a very dark to theatrically dark venue, such as a very small conference room or a small home theater, the LED illuminated displays of the future may be an extraordinary alternative. However, if the application requires a mid-size screen and the venue has any ambient light striking the screen, more lumens are required to produce imagery with high environmental dynamic range and suitable visual appeal.

Other than dedicated home theaters, the majority of single-chip projectors purchased today are employed in venues with some ambient light. As compelling as the benefits are, for that majority of front projection applications, LED will not provide a dynamic front projection solution any time soon.

Nonetheless, the ongoing evolution of LED illumination systems marks a huge improvement in single chip image quality and provides extraordinary benefits in long-term cost of ownership. As the technology progresses from working prototypes to finished products, DP’s future LED illuminated displays are certain to expand the single-chip projection marketplace. Simply stated, the technology dramatically improves the economics of employing projection systems in applications where superb color performance is required, but humble lumen output is sufficient.

Download hi-res versions of the photos above here: http://www.digitalprojection.com/news/zips/DP_LEDshots.zip

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A digital imaging pioneer and projector industry leader, Digital Projection International (DPI) manufactures and distributes an extensive and expanding line of ultra high-performance 3-chip and single-chip DLP® projection systems. These projectors are the reference standard for demanding applications such as large-venue, live-event staging, Fortune 5000, homeland security, education, medical and scientific research, command and control, digital cinema, commercial entertainment, worship and elite home theater.

Multiple company accolades include two Emmy® Awards for Outstanding Achievement in Engineering Development by the Academy of Television Arts and Sciences. DPI remains the first and only projector manufacturer to win the coveted award.