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SubscribeAt this writing, Casio's Green Slim portable projectors with their unique LED/Laser Hybrid light source are the most popular models on ProjectorCentral in the portable/mobile presentation category. Their popularity is easy to understand. They are thin enough to slip easily into a briefcase, and the reputed 20,000-hour life of the light source means there is no cost of replacement lamps down the road. These are the first truly bright projectors that do not operate on high pressure lamps.
We have now tested five samples in the Green Slim line, including four XJ-A130s and one XJ-A145. As previously reported here, four of the five fell short of the official lumen specification by at least 40%. On the other hand, one sample, an A130 rated at 2000 lumens, measured 1630 lumens in its brightest mode, and was obviously brighter than the others. Meanwhile, we have two trusted outside sources who both claim that their test samples are measuring much closer to spec than ours have.
It is now apparent that several factors have been contributing to the wide variance in lumen performance:
2. Variables in measurement procedures. Variances in lumen readings can also come from differences in test procedures. For example, conventional projectors with high pressure lamps tend to show an incremental increase in brightness as they warm up to stabilized operating temperature. Accordingly, we normally allow a test sample to run for ten to fifteen minutes to warm up and stabilize before taking a lumen reading.
Oddly enough, the solid state light sources used in the Casio Hybrid engine do not get brighter as they warm up. To the contrary, they diminish in brightness by about 10% as they warm up to their stabilized operating temperature. Thus, the brightest possible lumen readings on these units are obtained during the first minute of operation, immediately after powering them on. Casio states that they measure brightness within the first minute of operation to determine whether the unit is meeting spec. Due to this difference in procedure, our readings will always be lower since we wait until the light output has stabilized.
3. Ambient temperature. In addition to these factors, Casio informed us last week that the ambient temperature in the room will affect lumen output. We have never encountered this before. All of our lumen readings are done in a test area that averages 72 to 74 degrees Fahrenheit, or what most people would consider to be typical room temperature. Casio points out that the ISO 21118 protocol for lumen measurements calls for an ambient temperature in the test facility of 64.4 degrees F, or 18 degrees Celsius. In order to see whether ambient temperature does indeed affect lumen readings on the Green Slim models, we cooled our test area down to 64.4 degrees F. To our surprise, we did see an increase in brightness of 5%.
Our test sample that initially measured 1630 lumens is no longer that bright since it has been subjected to extended usage testing. It now has 200 hours of runtime on it, and its lumen output has degraded accordingly (more on this below). But had we measured that unit in a 64.4 degree ambient temperature when it was fresh out of the box, and had we measured it during its first minute of operation, our lumen reading would have exceeded 1900, or very close to the 2000 lumen spec.
Stability of the Light Engine over Time
Since the LED and laser are solid state light sources, can the user expect that this light engine will maintain its light output over its 20,000-hour anticipated life? Of course we cannot run them that long, but we did want to perform some initial life testing to see if we could detect any change in brightness over time. Therefore, we subjected two of our A130 samples to extended runtimes, turning them on and allowing them to run 24/7 until they accumulated 200 hours. The result is that both units lost about 25% of their maximum light potential during the 200 hour test. The unit that initially read 1630 lumens now measures 1216 lumens under the same test conditions. The unit that originally produced 1228 lumens now generates 949 maximum.
Two notes must be added here. First, 24/7 operation is not the normal duty cycle for a mobile presentation projector. We do not know whether this light engine would degrade to the same degree if the units were operated in a more typical fashion, running them in increments of an hour or two, then shutting them down. Second, our testing is done in Las Vegas at an elevation of 3100 feet. It is possible that the slightly thinner atmosphere would hasten the degradation of the engine compared to operation at sea level. However, we did operate one of the two units with the high altitude fan engaged during the entire 200 hour run, and we found no significant difference in percentage of lumen degradation between the two samples.
The lumen degradation in the extended use test was due to a diminishing of the intensity of green and blue, the two colors produced by the laser source. Red, which comes from an LED, stayed comparatively stable. As a result, color temperature will shift over the course of time as the relative strength of red, green, and blue change. We also noticed that the power consumption on the brighter of the two units diminished in direct correlation with light output. The unit that originally measured 1630 lumens was drawing 177 watts at that brightness level. At the end of the test it was delivering only 1216 lumens, but power consumption had dropped to 134 watts, a drop of 25%.
The Casio LED/Laser Hybrid engine is a fascinating new development in the industry. It is as novel as anything we've seen in the projector business. Casio designers certainly earn high accolades for creativity and originality. Yet as with anything new and untested, there are many questions left unanswered. How far will lumen output fall over time before it stabilizes? Will color temperature be acceptable once it does? How will the duty cycle, or type of usage, affect lumen degradation? Despite the theoretical 20,000-hour life, would the user want to replace the laser module much sooner than that to restore the projector's initial brightness? All of these things will be interesting to watch. And clearly a lot of people are watching. At this writing, the Top Ten rankings (popularity rankings) in the Portable category, in both XGA and WXGA resolutions, are dominated by Casio Green Slim models.
1. Early production flaws. Casio management states that "some of the initial Green Slim production units may not achieve their specified brightness" due to a "slight misalignment of the mirrors in the light path." Casio claims that they have taken corrective action to ensure proper mirror and lens placement during production. We do not know when this corrective action was taken or what serial numbers are involved. However, it appears that mirror misalignments help to explain why some units are measuring much closer to spec than others.
The Casio machine with LEDs for red is sort of like LEDs for low beam headlights. That is to say it's just a temporary work around until the technology gets better.
Similarly Ferdinand Porsche wanted a an electrical automobile but the batteries of 1905 weren't up to it - so he invented the hybrid. Batteries still aren't powerful enough more that a century later so we still have automotive hybrids. My guess is that LEDs will mature faster than batteries and no one will want a hybrid light source projector next year.
None of the Casio's bizarre problems that you so well documented and explained have been seen in non-hybrid projectors. I expect that in just a few months the Casio will become a exhibit for technology museums - in the fascinating kludge area.
How noticable is the speckle? All laser based displays should be evaluated for speckle.
