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It was some time ago when NEC Displays Solutions first highlighted the performance of its flagship SpectraView LCD monitor, the LCD2180 WG (Wide Gamut). In fact, NEC was showing a prototype as far back as March CeBit 2004. It was later showcased at Photokina 2004 and then fully developed for this year’s CeBit.
Now termed the Reference 21, this 21.3in LCD is finally available and boy was the wait worth it. You see, one of the issues with many standard LCDs is their inherently restricted colour gamuts which can play havoc with onscreen colours – the last thing you want when you’re pre-press proofing your images or if you simply need to ensure that the colours are accurately represented in a colour-calibrated professional workflow.
So what’s different about this monitor? Well I’ll come to the details in a minute, but it’s all to do with the light source used for the backlight. Let’s start with conventional LCDs. The backlight used in these displays takes the form of fluorescent tubes or cold cathode fluorescent lamps (CCFL) to be more precise. These tubes sit behind the liquid crystal layer and the red, green and blue filter matrices that make up each pixel.
In order to produce the range of colours needed to display a picture, the switching or rather the “twisting” liquid crystals determine the amount of light that passes through each primary colour filter and therefore the range of colours that can be produced. However, these CCFLs do not produce a pure white which in turn affects the colour temperature and ultimately the width of the monitor’s colour gamut. For an sRGB colour space, this method is fine and as we’ve seen in other monitors such as the Eizo ColorEdge CG220 and NEC’s SpectraView 1980 the Adobe RGB colour space can be reached, but this relies on some clever software to drive the switching along with filters that compensate for the CCFL backlight’s “not so pure” white light.
In other words the CCFL backlight determines the colour temperature and ultimately the colour space that can be reached. Now back to the Reference 21. NEC, instead of using CCFLs, has used an array of about 50 small red, green, and blue solid state LEDs, the sort you may find used in car interior lighting and headlamps, as well as in flash units on camera phones. These RGB diodes are mounted on a strip of PCB which runs along the bottom of the LCD screen.
As white light is a combination of red, green and blue the coloured light has to be mixed. This is done by using a mixing light guide as depicted in the diagram below.
This channels and mixes the RGB light components thus producing a variable wavelength white light. I say variable as this is a key aspect of the Reference 21’s innovative design - adjustable backlight colour temperature. In standard LCDs, the colour temperature is varied by software that partly switches off the RGB subpixels in order to hit the right colour balance. However, this reduces the light output. With an LED backlight the white point can be accurately adjusted between 5000K and 9300K without loss of brightness by varying the relative intensities of each RGB colour component produced by the individual LEDs.
Furthermore, there’s a feedback colour sensor mounted inside the back of the Reference 21 that monitors the colour temperature so that the display remains within its pre-defined parameters. This together with the fact that the LEDs have turn-on times that require virtually no warm-up period ensures that the colours are stable in no more than a minute. That means no waiting about for a colour accurate display to reach its optimum working state which I’d imagine would be a benefit in a fast-paced work place.