Display devices, such as projection systems, have been used for many years to project motion pictures and still photographs onto screens for viewing. For example, display devices, including front projection systems and rear projection systems, have become business tools, presentation tools, multi-media displays, home entertainment devices, signage, etc.
Conventional projection systems have employed a broad spectrum light source, a color wheel, an image-forming device, such as a digital micro minor (DMD), and various projection optics to generate and project an image onto a display screen.
Significant effort has been invested into developing display devices that produce bright, high-quality, color images. However, the optical performance of conventional display devices has often been less than satisfactory. For example, suitable projected image brightness is difficult to achieve, especially when using compact portable color projectors in a well-lighted room or in an outdoor environment. As an example, such display devices typically use high intensity arc lamps as their light source and then filter out all of the light except for red, green, and blue light and employ three separate light paths or some forms of sequential color modulator to coordinate color image data. Alternative projection systems, such as light emitting diode (LED) systems, are being developed. The interest in employment of LEDs as light sources for projection systems has been based in part on the potential of the increase in the light output of the LEDs. Moreover, LED light sources may have “instant-on”, long life (thus no lamp replacements needed for the life of the product), broad color gamut (color range), and no hazardous chemical (like mercury) contamination or disposal issues. However, current LED illuminated optical engines have been too dim to attract much marketplace interest and as such LEDs have not been able to become a replacement for standard high pressure mercury lamps or xenon lamps.