By now, the promises of laser illumination are well known: higher screen brightness with less heat on the imaging device, less power required for the lamp, and less demands on cooling systems. To a fair degree, the problems posed by laser illumination are also well-known: very high cost, and the potential for new types of visible artifacts, including speckle and metamerism (where multiple viewers tend to see different color casts). But hats off to Laser Light Engines this month for conducting an informative, if tightly controlled, demonstration of its current laser illuminator technology, and for bravely opening the kimono regarding laser light and 3D.
Three laser illumination demonstrations were conducted this month in the Los Angeles area, by Laser Light Engines, by NEC, and by Barco. (Barco’s demonstration was reported last month.) The LLE demonstrations took place in Technicolor’s facilities in Burbank, and NEC offered a demonstration nearby at the Marriott Hotel of its laser projector shown at Show East. As with Barco, LLE demonstrated synchronized content using two projectors, one laser illuminated, and one Xenon illuminated. The laser projector was color matched to the Xenon one. Disappointingly, LLE did not develop test material designed to reveal metamerism. Its highly structured presentation did not invite audience response to learn if color casts were observed, which would have indicated metamerism. LLE is quite confident that it has minimized the effects of metamerism, but it would have been more convincing if it allowed the audience to come to its own conclusion.
LLE considers itself to the be the expert in laser illumination, and it may be that it has earned this claim. LLE rejected the idea of vibrating the screen as a reasonable approach to solving the speckle problem, emphasizing that only a projector-based solution for speckle would be practical in the field. But the jabs at the home grown solutions from certain projector companies didn’t stop there. LLE claims no loss through fiber delivery of laser light to the projector, in opposition to statements from some companies. LLE solves this problem through a laser light illuminator design that optimizes spot size of the collimated laser light. LLE states that proper design will result in no loss through fiber, while improper design leads to the lossy behavior reported by certain projector companies. This is important, as fiber delivery of laser light to the projector can lead to remotely located light generators, producing the light for all projectors within a multiplex. It can also lead to mounting projectors in the auditorium, eliminating the cost of large projection booths from new construction.
LLE took the unusual and brave step of conducting a separate 3D demonstration, revealing a weakness of laser projection heretofore not widely discussed. Christie’s laser projector demonstration included 3D, but did so with a vibrating screen to eliminate speckle. Barco didn’t demonstrate the operation of its laser projector with 3D, but instead discussed spectral filtering as the optimum 3D system for laser illumination, as with Dolby 3D. NEC avoided the subject by not demonstrating its laser projector with 3D. LLE supported Barco’s claim that spectral filtering would lead to the most efficient and best looking 3D with laser illumination. But rather than demonstrate spectrally filtered 3D, LLE demonstrated 3D using a RealD polarizer and a Stewart silver screen. The results were quite revealing.
To understand the results, it’s first useful to understand how speckle is reduced in laser projectors. Speckle is the phenomenon that occurs when a pure wavelength of light bounces off a screen onto itself. A pure wavelength of light will produce alternating peaks and troughs in the light’s intensity. The alternating peaks and troughs are governed by random factors, such as instantaneous temperature of the screen, and air movement at the screen. The result to the viewer is that the light “speckles,” with alternating flashes of bright and dark.
In practice, several methods can be employed to mitigate speckle. Christie chooses to vibrate the screen at a sufficient rate to minimize its visibility. Electronic in-the-projector solutions require that multiple frequencies for each primary be used, such that the speckle produced by one frequency of light will be diminished when accompanied by other frequencies. Another technique is to modulate the polarity of the laser light, such that a bounce from a non-polarity-preserving screen (i.e., non-silver) does not create perfect peaks and troughs to the viewer. LLE uses several methods to adequately diffuse speckle, including polarization. Thus, when LLE’s projector is displayed on a non-silver screen, no speckle is visible. But when projected on a silver screen, speckle becomes remarkably apparent. Viewing actual 3D movie scenes using polarized 3D leads to somewhat acceptable results, but not remarkable results. In one fell swoop, LLE revealed why Christie chooses to vibrate screens for its 3D demos, and why Barco quickly shelves any discussion of polarized 3D in favor of spectrally filtered 3D.
LLE is smart enough to not reveal a problem with polarized 3D without having a solution in its back pocket. But it isn’t ready to show its solution to Hollywood just yet. I was assured, though, by the VP of Strategic Marketing for IPG, which ranks among the top five laser manufacturers in the world, and who was present at the event, that LLE’s solution is looking good.
3D is the most important application for laser illumination, as, after all, exhibitors don’t have a problem lighting up 2D screens with Xenon lamps. The importance of providing quality 3D on polarized screens using laser illumination is one of economics and operational efficiency. Polarized 3D solutions are now employed in the majority of 3D screens around the world, and in the US, polarized glasses are subsidized by distributors. While better light efficiency may be possible with spectrally filtered 3D solutions, the glasses are not cheap. It’s also undesirable to mix different types of glasses within a complex. Few exhibitors would employ spectral filtering on all screens in a complex, particularly if only one or two screens in the complex have a laser projector. It would seem reasonable to expect numerous exhibitors using polarized glasses in non-laser-illuminated screens to also prefer polarized glasses in their laser-illuminated screens.
The recent run of laser illuminator demonstrations in the Los Angeles area have been quite revealing, and demonstrate that as more is learned about the strengths and weaknesses of laser illumination, more work is needed before the technology is ready for deployment. But it’s getting better all the time.