LCD display: when screens have become flat

Today a high resolution flat screen is part of normal office equipment. LCD technology for monitors is only 25 years old and has been reluctant to establish itself. Georg Schnurer reported in “c’t” 6/1994 of a 10.4-inch color monitor with VGA resolution (640 × 480 pixels), which at the time was being offered for an impressive 10,000 D-Marks. The exorbitant prices despite the pathetic resolution and enormous dependence on the viewing angle were due to the production of immature LCDs – there were rumors at the time of rejection rates above 70%.

In the following two years, the first 15-inch diagonal LCD monitors were introduced to the market and the resolution rose to 1024 × 768 pixels (XGA). With over 6,000 D marks, the devices were still extremely expensive. In the 1990s, bulky tube monitors (CRTs, Cathode Ray Tube) dominated desks: good devices with a 20-inch diagonal displayed 1280 × 1024 pixels (SXGA) on a visible screen with an 18-inch diagonal – part of the screen disappeared behind the tube cover.

The beginning was analog

LC displays initially weren’t able to show their advantage over CRTs – a crisp, flicker-free display – because they operated in analog mode just like CRTs. The monitor manufacturers have had to re-synchronize and digitize analog video signals from the graphics card. As a result, some LCD monitors blinked.

Finally, at Cebit 1998, the first graphics cards were presented that had digital signal outputs in addition to analog outputs. In the same year, “c’t” tested large-scale LCD monitors for the first time: twenty devices with diagonals between 13.8 and 15 inches for 2700-4800 D-Marks. Their viewing angles were extremely narrow – when viewed from the side, the image was milky, and when viewed from below, it was often inverted. We still celebrated flat screens.

In the aforementioned comparison test, we also got our hands on the first purely digital LCD: Siemens-Nixdorf delivered it with a suitable graphics card, it showed 1024 × 768 pixels on a diagonal of only 35 centimeters (13.8 inches) and it cost a whopping 3700. D-Mark.

We brought the first 18-inch laboratory “c’t” for the number 18/1998. They come from NEC and Eizo and with 8,000 D-marks cost four to six times more than a comparably sized CRT monitor. We found the screen size to be excellent, the image quality only average. Over the next few years, prices dropped rapidly, something that supermarket chains also took care of: tracking of offers led to queues in front of Aldi, Plus & Co. In mid-2001, a 15-inch device cost only 700 D -Marks. However, most of the devices used TN panels which depended on the viewing angle and only had an analog signal input. It wasn’t until around 2003 that VA and IPS technology monitors with stable viewing angles became affordable.

Increasing diagonals and above all higher resolutions have finally forced the switch to digital input. As is common with many fundamental changes, this move has resulted in a mishmash of digital connection options, including P&D, DFP, and DVI. For Apple’s DVI variant ADC, you even needed your very bulky power supply. In the entertainment electronics segment, High Definition Multimedia Interface (HDMI) eventually prevailed, while DisplayPort established itself in the PC industry. Many PC monitors still have HDMI so far and some have even VGA.

Some LCD manufacturers from the very beginning are still represented on the market today, such as BenQ, Philips and Samsung. But do you still know Belinea, Natcomp or Highscreen?

LEDs made monitors thin

A milestone was the change in the backlight: instead of cold cathode fluorescent lamps (CCFLs), small light-emitting diodes (LEDs) have been illuminating the LCD background since 2006. Initially, manufacturers used colored RGB LEDs in the backlight, which made the monitors extremely colorful, but also extremely expensive.

The first inexpensive blue LEDs, whose light was converted to “white” light via yellow diode caps, were found in monitors around 2008. While LED backlighting had long been common in notebooks, the complete switch to More energy-efficient LED technology in PC monitors didn’t happen until after 2010. With the mercury-containing CCFL tubes, even the glint on the background of the screen disappeared, the monitor housings became lighter and the displays still more leaner.

3D is in the room

Since 2009 there has been a 3D interlude: monitors whose stereo images could be viewed by users with red-green glasses, bulky shutter glasses or lighter polarized glasses, and awkward driver settings. In the same year, the format of flat screens went from 4: 3 or 5: 4 to wide formats such as 15: 9, 16: 9 or 16:10. This was not due to the changing viewing habits of users, but simply to new panel factories: to make full use of the factories for large-format flat screen televisions, monitor panels were also produced.

Many pixels help a lot

The Full HD resolution of 1920 × 1080 pixels, already common on TV, then caught on even in the monitor. Since around 2010, 27 and 30-inch screens have been offered with even more pixels, i.e. with 2560 × 1440 (16: 9) and 2560 × 1600 pixels (16:10).

In 2012, the first high-end devices with ultra-high resolution (UHD, 4K) such as the Eizos FDH360 appeared in stores for 25,000 euros; since 2013, 4K resolution for monitors has become more affordable. Initial connection problems soon eased, and prices fell rapidly too: two years later, 4K monitors with TN panels cost just 500 euros.

Screen diagonals increased with resolution: 32-inch models with a diagonal of 80 centimeters suddenly became conceivable for the desk. In the edition of 11/2015, »c’t« therefore checked whether the cheapest 4K TVs could also be converted into large monitors.

Starting around 2013, extra-wide monitors with 2560 × 1080 or even the finest 3440 × 1440 pixels came into fashion. Many of them were slightly curved to keep the distance between the screen surface and the viewer’s eye constant. The great demonstrations were initially ridiculed, today they are indispensable.

In 2015, Apple, Dell and HP unveiled the first 5K displays with nearly 15 million pixels, and two years later Dell triumphed with the first 8K monitor with 33 million pixels, doubling again. However, such giants are still reserved for a few very expensive devices.

Synchronization for players

In 2015, even gaming fans were thrilled with the first monitors whose image output worked in time with the frames provided by the graphics card. For Nvidia’s G-Sync, the monitors required a fan-cooled module to ensure synchronization. For AMD’s FreeSync, a variant of Adaptive Sync specified by VESA, on the other hand, no expensive modules were needed – initially there were no displays for either technology. This field training didn’t end until 2019 when Nvidia had an understanding and introduced so-called G-Sync compatible devices.

In 2017, the USB-C port entered monitors as a video input. Because it also transmitted USB data and power in addition to DisplayPort video signals, the monitors could be used as notebook docking stations.

More contrast for videos

The high-contrast display was initially reserved for TV displays until it appeared on PC monitors in 2017. However, early HDR monitor tests were sobering – we couldn’t see any difference between the display with and without HDR. VESA did not specify high contrast playback on PC monitors until late 2017 in the DisplayHDR standard.

The next step in increasing contrast was made possible by the mini-LEDs, which were now evenly distributed across the back of the display instead of the edge of the display and could be controlled individually. Asus unveiled the first device with countless tiny LEDs for full-array local dimming (FALD) in 2019 with its 32-inch ProArt monitor with mini-LEDs, and in early 2020 Apple followed suit with Pro XDR display. The prices for these high-end monitors – costing between 3,000 and 6,000 euros – are the same that were to be put on the table for the first LCD monitors in the mid-1990s.

That’s next

Mini-LED backlighting will eventually go mainstream in monitors. The alternative to this would be organic displays, but there will likely be no OLEDs in monitors for the foreseeable future – scaling to smaller diagonals only works very slowly, even in the TV industry.

True LED displays, where each pixel is implemented with three light emitting diodes, on the other hand, may first find their way into small, very special and therefore very expensive monitors. Until then, however, LCD technology will dominate the world of monitors for a long time.