The two lowest price 4K projectors currently on the market are the ViewSonic PX727-4K, rated at 2200 lumens, and its brighter version, the ViewSonic PX747-4K, rated at 3500 lumens. Both are priced at $1299.
These two models are identical projectors in all respects except for the color wheel. The PX727-4K has an RGBRGB wheel and the PX747-4K has an RGBW wheel. The white segment in the PX747-4K's wheel is what gives it the extra lumen power. Since they are the same except for issues related to the color wheel, we will focus just on those differences in this article. See the Viewsonic PX727-4K review for all other details on these two models.
What difference do the color wheels make?
These two color wheels present us with a trade-off between total white light output (ANSI lumens), and color brightness. In practical terms, this means that white elements in a picture will appear brighter on the PX747, while colored subject matter appears brighter on the PX727.
To illustrate, think about the Universal Studios splash screen, with the bright white Universal Studios logo circling the Earth with deep space as the background. When projecting this particular image, the PX747-4K looks brighter and higher in contrast than the PX727-4K. The reason is that the black levels are essentially the same, but the white lettering of the logo is much more brilliant on the PX747. The picture has more pop and vibrance on the PX747.
Now think about the reddish brown landscape scenes in The Martian. In these scenes there are typically no white elements but there is a lot of rich color. With this type of picture the PX727 is, surprisingly, both brighter and higher in contrast. Not only do you see a deeper color saturation, but the overall picture is actually brighter as well, and the combination of higher brightness and saturation makes the picture look obviously higher in contrast. This picture has more pop and vibrance on the PX727.
Why does this happen? Color brightness measurements
The reason this happens is due to the interaction between white brightness and color brightness on the two projectors. By white brightness, we mean the total brightness of the color "white". By color brightness, we mean the sum total of the projector's lumen power as it projects red, blue, and green as independent colors. Since the PX747-4K has a white (or clear) "filter" in the color wheel, it is able to project a lot more white light than it would be able to if it were passing all of the lamp's light through the red, blue, and green filters, as the PX727 does. So on the 747, a lot of white light hits the screen that has not been modulated through color filters. The PX727 can deliver white as well, but it does so by turning on all red, blue, and green channels at once, and the combination makes white.
The ANSI lumen spec measures the total amount of white light a projector can produce. In Movie mode (a setting calibrated for best video performance on these two projectors), we measured the PX727-4K at about 1100 ANSI lumens. By comparison the PX747-4K's Movie mode puts out about 1600 ANSI lumens. In both cases our measurement was about half of the projectors rated maximum lumen potential. This is typical for video optimized settings on many projectors.
However, since ANSI lumens measures only white light, this is not the entire story. If you measure the total amount of red, blue, and green light independently on these two projectors you get quite different results. On the PX727, the luminance of R + B + G adds up to 100% of the white light output. On the other hand, on the PX747-4K the R + B + G channels add up to 57% of white output. So while the PX727 puts out about 1100 lumens of color brightness, the PX747 puts out only about 900 lumens. It is no wonder that the color-rich Martian landscape look brighter and more saturated on the PX727.
A similar result happens in Standard mode. We get about 1350 ANSI (white) lumens on the PX727, and 2000 lumens on the PX747. However, color brightness is only 45% of white on the PX747 in this mode, while color is 82% of white on the 727. Here again, the absolute color brightness is actually higher on the 727 than on the 747, despite its lower ANSI lumen ratings and measurements.
Bright mode is distinctively different on these two models. While Bright mode on the PX727 has a rather noticeable greenish cyan tint, the PX747 delivers a brilliant white 3100 lumens with very little obvious color bias. This is quite unusual for a projector's brightest operating mode. However, in Bright mode, despite its brilliant white, the amount of color light making it to the screen drops to 26% of white. The overwhelming amount of white light in the mix causes color subject matter to appear quite dull and low in saturation. So Bright is not a good operating mode for video/film. But it is an outstanding option for high resolution presentation of black/white text documents, financial spreadsheets, etc.
As a matter of fact, the PX747-4K should be strongly considered as a conference/boardroom projector in situations where the subject matter is primarily numbers, text, black and white bar graphs, etc. The reason is that the PX747-4K is absolutely unique in the market for its combination of 4K resolution, a brilliant, neutral white screen, and very low price. Its video quality, though not as rich and balanced as the PX727-4K, is certainly usable when video is a secondary element in the mix of presentation materials.
Since the PX747-4K is identical to the PX727-4K in all respects other than the color wheel we would end up duplicating a lot of the Viewsonic PX727-4K review. So read that review to get most of the basics of these projectors, and then factor in the variables on color brightness discussed here to decide which might be the better choice for your use.
In general, we strongly prefer the ViewSonic PX727-4K for classic home theater because the picture has higher color saturation, contrast and brightness in most full color imagery. And 1100 lumens of color light output is ample for most dark theater applications. We can't think of any situations in which we would opt for the PX747-4K over the PX727-4K if the intended use is full color video/film display. But if you're looking at 4K projectors for business/conference room use, it's a different ballgame. The ViewSonic PX747-4K has got some serious lumen muscle in black/white 4K presentation that the PX727 simply cannot match. And for this very unique combination of features at $1299 it gets 5-stars for value.
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