Leaving aside the subject of High Dynamic Range (HDR) projection, which was popular at NAB but not on the radar at CinemaCon two weeks earlier, projector manufacturers are touting the 3D benefits of laser-illuminated projection. Laser illumination eliminates the unwanted infrared spectrum of Xenon bulbs, significantly reducing the heating of imaging devices, and allowing more power to be applied. The laser projection light path also provides the means to more efficiently couple the power of the light source to the imaging device. Both improvements lead to the potential for very high levels of light on-screen. Exhibitors, however, aren’t in dire need for brighter 2D images. But they are in need of brighter 3D images, and here is where the promise of laser projectors has perhaps been overstated.
At question is whether it is realistic to expect laser projection to become the cornerstone for 14 ft-L 3D. The finger can be pointed towards manufacturers for raising this expectation. Touting that one’s laser projector can emit 60-70K lumens of light has caused all kinds of hope in Hollywood that 14 ft-L 3D is achievable, at long last. To further relay the message, Barco and Christie have each devised different versions of 6-primary laser projection, where three primaries can be directed to one eye, and the other three to the other eye, using spectral filters in the glasses. (Spectral filtering is the technique made popular by Dolby 3D, and also utilized by the now defunct Panavision 3D system.)
Spectral filtering has proven to be the most inefficient method for 3D with Xenon lamps, because so much of the light power across the spectrum must be thrown away to reduce it to the narrow bands of light required by spectrally filtered 3D glasses. With laser projection, however, the method is set to become the most efficient way to project 3D. This is because the light power of the projected light is entirely in the 6-primaries, with no light (in practical terms) thrown away by filters. This results in 3D efficiencies such as those advertised by Christie of 42% – 45%, out of a theoretical maximum 3D light efficiency of 50%. (50% is the theoretical maximum as only 50% of the available light can be seen by one eye.)
Using the lower range of Christie’s spectral 3D efficiency, one would need 63,000 lumens to produce 14 ft-L 3D on a 1.8 gain 80-foot screen. That’s very close to the 72,000 lumen capability that Christie offers. But what if the exhibitor can’t use, or doesn’t wish to use, spectrally-filtered glasses? For example, some exhibitors are locked into 3D contracts that require them to use a silver screen. RealD advertises an efficiency of 28% for its XL system, requiring 77,000 lumens to produce 14 ft-L on an 2.2 gain 80-foot screen. The same 63,000 lumens would produce 11.5 ft-L 3D, a very respectable number, but not the hallowed 14 ft-L. In addition, one would probably have to add low-frequency vibrators to the screen to mitigate the loss of speckle reduction introduced by polarization-preserving screens. (No, this is not a porn joke.)
Barco’s laser projector is rated by Barco to be only 22% efficient with spectrally filtered glasses. (This number was given in Barco’s laser projector presentation at TSC this month. One can essentially take the numbers for Christie’s projector and divide them by two. The 22% figure seems exceedingly low, and will be further investigated to make sure this wasn’t a typo. However, Barco also went on record with the ASC this month to defend DCI’s recommended 7 ft-L 3D as a reasonable light level for laser projection.
NEC also has a laser projector. But is is left out of this evaluation as it’s not targeted for high brightness 3D applications. Instead, NEC’s laser projector is designed, built, and marketed as a cost-effective replacement projector for screen sizes up to 9.5 meters. It is not a 6-primary device, and offers no additional efficiency over Xenon for 3D.
Overall, given that cinema owners will only be interested in installing laser projectors in the largest of auditoriums, getting to 14 ft-L will not be an easy task. This is an important point in light of recent discussions in the ASC Laser Technology Committee, and at this month’s NAB, where more than one studio emphasized the holy grail for 3D to be 14 ft-L. They argue that it’s a waste of investment for exhibitors to buy fancy new projectors that fall short of this goal. It was clear that this isn’t a position that will simply dissipate on its own, and it’s likely to become the new mantra for 3D. The ASC Technology Committee, whose cinematographers would love to see 14 ft-L 3D everywhere, didn’t waste any time moving to back the studios. It’s entirely possible that this argument will lead to a modification of DCI’s High Frame Rates Digital Cinema Recommended Practice, where 7 ft-L +/- 2 ft-L is quoted as the target light level for 3D.
In spite of the attention this subject receives, the actual market for laser projectors is expected to be quite small. The cost per laser lumen is said to run in the $8-10 range. Regulatory approval is still years away, although 5-year waivers can be had, and certain progress has been made at the standards level, as evidenced by the newly approved IEC 60825-1 Edition 3 specification. The revised specification carves out the ability for laser-illuminated projectors to evaluate risk assessment using the less restrictive rules under IEC 62471. This is an important step in the long journey toward changing government regulations around the world regarding use of laser illumination in public places. With a revised IEC specification to point to, it is hoped that eventually government agencies will relax their rules.