Epson presented an interesting demo at CES this year. It involved a relatively new video-measurement standard adopted by SID (Society for Information Display) called color light output (CLO). Most of us are familiar with white light output (WLO), more commonly called peak white level. And of course, white is simply a mixture of red, green, and blue, so if you were to measure the maximum level of the three primaries and add them together—which yields the CLO—you should get the same value as the peak white level.
However, this is not always the case. In particular, single-chip DLP projectors sometimes include a white (clear) segment in the color filter wheel to increase the peak white level, and some filter wheels also include segments with one or more of the secondary colors (yellow, cyan, magenta). Therefore, when you add the maximum levels of red, green, and blue, the result is lower than the measured peak white level, because those extra segments are not used in the RGB measurements, whereas they are used in the white measurement.
The effect of CLO was clearly evident in the side-by-side demo shown in the photo above. Two 720p projectors with the same rated WLO were fed the same signal from one Blu-ray player using an HDMI splitter, and each projector was set to its brightest out-of-the-box mode with no other tweaking. They were firing onto identical screens (Screen Innovations Lunar Gray, 16:10, 120 inches diagonal, 0.85 gain).
On the right is the image produced by an Epson 750HD, while the image on the left was produced by an Optoma GT750E. Both have a WLO rating of 3000 lumens, and measurements made in the venue were quite close to this value—2920 for the Epson, 2840 for the Optoma. However, the measured CLO was quite different—2950 for the Epson, 980 for the Optoma. As you can plainly see, the Epson's image is a lot brighter than the Optoma's, and the colors are not the same.
You might think the CLO measurement is designed to make the specs of LCD projectors look better than those of single-chip DLPs. But the measurement methodology was developed by SID, which has no skin in that game. Also, any 3-chip design, including LCD and LCoS as well as 3-chip DLP, is likely to have equal WLO and CLO. Finally, there are single-chip DLP projectors—those with only red, green, and blue segments in their color wheels—that have the same WLO and CLO measurements.
For more on this, visit www.colorlightoutput.com, where you will find lots of interesting info, including the results of independent third-party tests of many projectors. Those results include the manufacturers' WLO specs and independently measured CLO; I'd prefer to see independent measurements of both.