2510332 - February 2009
4.3.4 Image Quality
It is important to understand the product application for the projection-lens requirements. For example, computer graphics use demands sharp pixel-edge definitions, requiring higher MTF specifications (see section 3.2) than video lenses. This is because meaningful data is mapped pixel-to-pixel from the source to the screen. By comparison, video-only applications may actually look better if the pixel-edge definition is smoothed or blended to be less noticeable. This means MTF requirements may be relaxed significantly, because it is rare that meaningful video image data is contained at the Nyquist resolution frequency. Likewise, misconvergence usually is less noticeable in video images (for CRT and three-panel displays), so lateral color effects also are likely to be less noticeable and may be relaxed. Cost trades can be made by considering expected applications in this manner.
One increasingly popular alternative to arc lamps for DLP systems is Light Emitting Diodes, or LED’s. There are several advantages to LED sources:
Long life (if properly managed thermally) typically exceeding product lifetime. Thus, no lamp changes required.
No gravity restraints on orientation of the LED, which allows the projector to be oriented in many different directions (for example, pointing up to a ceiling). There may be constraints related to the thermal solution, however.
Fast response time makes them suitable for Field-Sequential-Color (FSC), the mode used for single-panel DMD systems. Capable of very high field rates for smooth motion video and no color breakup. Switching LED’s on and off eliminates the need for a color wheel, the only moving part in a conventional lamp based DLP system. Eliminates noise of color wheel and factory handling issues.
Can be dynamically dimmed or boosted to greatly improve contrast or brightness or create multiple white point and color gamut modes.
Environmentally friendly; no Mercury disposal. No rupture containment required. Highly saturated color gamut.
Fast performance improvement cycle. Many companies, scientists, and engineers are working to improve LED efficiency for general lighting, signage, automotive, and industrial use. Projection industry can benefit from this fast learning cycle.
No UV or IR filters needed.
Alternate Light Sources and Systems
May not be reproduced without permission from Texas Instruments
Copyright 2009 Texas Instruments Incorporated