High-Brightness Light Source for Ultra-Short-Throw Projector
June 3, 2015, Society for Information Display Symposium, San Jose, CA—Yuki Maeda from Sony described the efforts in developing a high output light source for 4k projectors. The intent is to provide an alternative to flat panel displays for in-house use.
The emerging 4K market can be handled reasonably well for smaller screens on flat-panel displays, however most users want to watch 4K content on very large screens. The problem with large screen displays is they are large and heavy, and can be intrusive as a blank piece of glass on the wall. In comparison, a projector can provide images over 100 inches while being in interior friendly.
Ultra-short-throw 4K projectors can provide large images without needing a long distance from projector to the viewing surface. In addition, solid-state light source provides high levels of output without requiring cooling fans as a incandescent lamp would. The basic system generates a white light source by using 2 blue lasers. One laser illuminates a rotating phosphor wheel which emits yellow light which is split into red and green components through a series of dichroic mirrors.
The wheel is reflective and has a high thermal conductive substrate for enhanced cooling. Separating the two drive lasers allows independent control of blue and yellow light output, and allows for optimization and improves noise characteristics. The binders in the resin for the phosphor wheel has an inorganic base to improve phosphor wheel lifetime under strong laser excitation. In addition, the reflective phosphor wheel has a heatsink on the backside to improve cooling characteristics.
The challenge in using laser illuminated phosphors is that increasing light intensity causes a decrease in florescence emission. This drop is due to brightness saturation and temperature quenching. With an excitation light density of 128 W per millimeters squared, conversion efficiency improved by a 28 percent with a florescence output of 87 Watts. The combination of improve cooling and different phosphor materials and binders enables high light output and also shows very little degradation over 10,000 hours lifetime testing.
