Brightness and Spatial Resolution of a Prototype, Green-Laser Projector Measured for Various Display Screens and Image Sizes

摘要

Laser light has many unique characteristics, such as coherence and speckle, and in addition, the individual pixels formed by the raster structure of a laser projector have very little persistence. As a result, there is some question as to whether the luminance of laser-projector imagery can be measured accurately, and whether that imagery will appear the same as more conventional imagery of the same luminance. In a preliminary attempt to address these questions, we have measured the luminance of a cathode ray tube (CRT) and a laser projector and have directly compared their measured luminance and perceived brightness. There were no apparent difficulties or complications in measuring the luminance of the laser projector using a standard spotmeter. However, a laser-projector image judged to have the same brightness as a CRT image had a measured luminance that was about 14% less. Thus, the limited and preliminary data reported here indicate that a laser image of the same luminance appears slightly brighter than that of a CRT. There were some differences between the CRT and laser measurements made with a spotmeter and with a CCD photometer. Although the differences were relatively small for display luminances less than about 5 fL, this issue should be addressed further with future versions of the laser projector. There appears to be a real difference in the spatial resolution measured at the center and edge of imagery projected onto the three screen tested. However, given the variability of the measurements, there is no clear evidence of significant differences among the three screens tested in center-to-edge spatial resolution. The relatively small (5.5% overall) reduction in spatial resolution as projected image size was reduced represents an apparent advantage of the laser projector over other displays. Further data are needed, however, to determine if this reduction in spatial resolution is significantly greater at the edge of the image.