Samsung SyncMaster XL20 LED-backlight monitor

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POWER MEASUREMENTS

The XL20 was plugged into a Seasonic Power Angel to obtain AC power measurements in various states. For comparison, the 4-year old 19" BenQ FP991 LCD monitor was also measured under the same conditions. Data from a Samsung 931BW 19" widescreen LCD monitor is also shown. The optimal desktop results are the most relevant.

AC Power: Samsung XL20 vs other LCD monitors
Setting
XL20
BenQ FP991
Samsung 931BW
Optimal, desktop
67W
34W
26W
Max brightness, white screen
72W
36W
31W
Min brightness, white screen
36W
30W
15W
The XL20 is the only monitor in the group to feature Active Power Factor Correction. Its PF was consistently 0.97 or higher, while the others were at 0.61~0.67. High PF is preferable (greener) for more efficient delivery of AC power.

The results were shocking. The XL20 consumed twice as much power as the FP991, and over 2.5 times the power of the Samsung 931BW LCD monitor reviewed a few months ago. No wonder it needs a fan!

The following questions were emailed to Samsung Canada, who supplied the XL20 sample:

Why does the XL20 have a fan? LED backlight monitors are supposed to be more energy efficient. Why does the XL20 take double the power of other CCFL-backlight LCD monitors?

The answers took some weeks to return from techs in Korea, apparently, in a kind of shorthand:

"Luminance efficiency of LED is yet less than CCFL's as of today but it keeps getting better. The efficiency of White LED is a little less than or almost same as CCFL's but the efficiency of three color LED (R,G,B) is much less than CCFL's, which XL20 is implemented with since it gives out much wider color gamut than CCFL and reproduces even better colors. To prevent the increase of internal temperature due to the low efficiency of three color LED, the fan is inside. Due to the efficiency mentioned above, it is about 1.3 times more than normal 20” LCD monitor with 1600 x1200 resolution."

The answer is self-explanatory, and the mention of three color LEDs leads us to a consideration of the backlight technology inside the XL20.

CFL vs. LED BACKLIGHTING

A discussion of these technologies can become quite complex, because there are several variants of both. I am no expert on LCD backlight technology, and my knowledge is based only on what I've researched for this and a couple of other monitor reviews in the past. Here's a summary of what I found:

Conventional flat-panel Liquid Crystal Display monitors use Cold Cathode Fluorescent Lamps for backlighting. The light of the CCFL spans the visible spectrum, and this mixture of frequencies is seen as white light. Each pixel has three filters, one red, one green, and one blue; adjusting the amount of light through those filters results in various mixtures of red, green, and blue light. Because of the way the human eye works, different mixtures of those primary colors allow a person to perceive all the different colors across the visible spectrum.

The CCFL is usually a thin tube that's about as long as the width of the screen. A white diffusion panel behind the LCD redirects and scatters the light evenly to ensure a uniform display. On its way through filters, liquid crystal layers and electrode layers, some of this light is lost. The CCFL does not emit light perfectly evenly all across its surface, which explains the generally greater brightness behind the screen.

Instead of a CCFL, Luxeon and Triluminos technologies use an array of red, green, and blue LEDs; again, humans perceive the mix of these lights as white. But when, for instance, the green and blue are filtered out of a pixel, you get the pure, saturated red of a red LED (unlike with the "white" light source of the CCFL, which permits a range of red frequencies through the filter). These purer primary colors yield better-looking mixtures, as well.

Samsung's product literature actually has very little real information about its LED backlight. NEC, the first company to offer an LED-backlight LCD monitor, provides more details about the technology in their 2180WG-LED-SV. Judging from the text and images shown in this review by Digital Video Editing, a strip of 48 LEDs is used in place of a CCFL, apparently. A flash animation about Samsung's "MagicSpectrum", which covers both CCFL and LED backlight monitors, suggests a different layout in the Samsung XL20 where the LEDs are more or less evenly placed across the back of the light diffuser. However, it's also not clear whether the animation is a truly accurate depiction, as its primary function is marketing.

What about the LED-backlit LCD monitors on the latest notebooks that supposedly increase battery life and power demand? They are different in that use only white LEDs are used, not three different color LEDs as in the XL20.



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