ASUS PB278Q 27-inch WQHD PLS LED Monitor Review

ASUS PB278Q - Brightness

ASUS advertises a relatively high 300 nits (note Nit = cd/m²) maximum brightness level.  Since PLS has an advantage that each of the cells allow more of the backlight to pass through, it becomes easier for manufactures to deliver brighter displays without boosting the power consumption.  Our measurements showed that the PB278Q could deliver 301.38 nits of brightness at the center of the display, so its specification is hit right on the head.  Also important is how dim it can go.  For those who might plan on using the monitor in a dim/dark office, you may require very low brightness to prevent unwanted eye strain.  The PB278Q, on the other end of the spectrum, was able to get as low as 58 nits, so everyone should be pretty well-covered for your brightness preferences.

Maximum Brightness:  301.4 Nits

Minimum Brightness:  58 Nits



Contrast Ratio

The contract ratio at the center of the screen was very strong.  With the black level at maximum brighness at 0.32 Nits, the true Contrast Ratio is an impressive 930:1.  At half brightness (calibrated to 150 Nits), the black level sinks to 0.15 Nits with a White Level of 144.34 Nits, which gives a true contrast ratio of 974:1.  Again, we're happy with the results here.


Backlight Uniformity

To measure the backlight uniformity, we took black and white levels at 5 locations vertically and horizontally (25 total positions).  The edges and corners were measured as close as we could get our X-rite i1Display Pro, which is within about a quarter inch.  We took uniformity measurements at full brightness (~300 nits) and at roughly half brightness for a typical dimmer usage, calibrated to 150 nits brightness.


150 Nits (Half Brightness)

300 Nits (Full Brightness)

Black Level (Nits)
ASUS PB278Q Review - Half Brightness Black Level Uniformity ASUS PB278Q Review - Full Brightness Black Level Uniformity
(Click to see full size version)
White Level
ASUS PB278Q Review - Half Brightness White Level Uniformity ASUS PB278Q Review - Full Brightness White Level Uniformity
(Click to see full size version)
Contrast Ratio
 ASUS PB278Q Review - Half Brightness Contrast Ratio  ASUS PB278Q Review - Full Brightness Contrast Ratio
(Click to see full size version)


Similarly (and also related) to the color results, we see the corners and the sides having the greatest deviation from the center.  The center down to the middle-bottom tends to be very uniform, but the corners are bright while the left side is a bit dim.  While our sensitive i1Display Pro can detect these "bright" corners and their effects on the Delta E color measurements, with an all-black screen the backlight bleeding isn't detectable by my eyes.  I tried using my DSLR with varying exposures to see if I could get a good visual of any backlight bleeding, but even my DSLR couldn't detect anything definitive.  Overall, the backlight uniformity is pretty good, but the left edge definitely deviates more abruptly from the rest of the panel.  The contrast ratios actually end up being very uniform across the screen, with, again, the largest deviations seen in the corners.


Backlight PWM

As you may or may not know, display brightness is often controlled by PWM (pulse-width modulation) which basically modifies the "on-off" waveform.  The more "on" time and less "off" time of the wave, the brighter it will be.  Most PWMs use a similar frequency, and once the off time becomes long enough, a flicker is produced.  Flicker is more pronounced in LEDs because there is very little illumination "bleeding."  LEDs switch off-and-on very quickly, where you may notice CCFL (Cold Cathode Flourescent Light) bulbs in your house "glow" when turned off.  A very good informational article on monitor PWM can be found at TFTCentral.




The image above is the PWM frequency of a 1/25" exposure time while slowly panning.  We can count 9 lines over 1/25 of a second.  Crunching a few numbers, (9 lines / (1/25 seconds) = 225 Hz PWM frequency.  225 Hz is a fairly high PWM frequency, and even at the lowest brightness levels we still fail to notice flicker.  Flicker can cause significant eye strain, especially over the course of a day, so this can really be a deal-breaker for those who plan to use it for work.  Fortunately, you shouldn't have any issues, even if you plan to use it at low luminance levels in a dim environment.

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# tuta 2013-02-18 19:07
$649?? humm, I prefer 29" 21:9...