What Things to Verify before buying a PC Monitor.

Decrypt the technical characteristics

If computer screens are more and more beautiful objects, the quality of the image remains top of mind. However, this quality is conditioned by multiple parameters, sometimes hidden, that you must decrypt in order to better direct the choice of your PC screen.

The luminosity

Expressed in candela per square meter (cd / m2), the brightness of the screen slab quantifies the maximum luminous intensity emitted by the slab of the screen (the scientific rigor would rather impose the notion of luminance). The higher the value, the brighter and more visible the display, even in a brightly lit room. The brightness is between 250 and 400 cd / m2 approximately. However, it is difficult to separate two screens from this criterion alone.

The contrast

The contrast of the screen tile is the ratio of light intensity between the extreme white point and the extreme black point. In this case, a ratio of 400:1 means that the white dot is 400 times brighter than the black dot. It is therefore a parameter related to the brightness.

In general, a contrast ratio of 500: 1, in the context of office use, is sufficient. It goes up to 1000: 1 and well beyond for PC screens dedicated to the world of images in all its forms (desktop publishing, CAD, etc.). Be careful, this is a so-called "typical" contrast ratio. Manufacturers, for their part, announce a so-called "dynamic" contrast, which exaggerates the figures. Do not be fooled!

Angles of vision

Thanks to a good viewing angle, the contrast and colorimetry are preserved even if the screen does not face the users.
The viewing angle of the computer screen is indicated by two consecutive values, expressed in degrees, in the horizontal and vertical directions. These are the maximum angles beyond which the image is degraded (sharp drop in contrast and colorimetric fidelity).

The viewing angle depends on the slab technology used. For example, IPS and PVA panels have very wide viewing angles, typically 178 ° / 178 °. This is ideal for collaborative work, so that everyone in front of the screen has a vision identical to that of their neighbor.

On the contrary, the TN slabs do not exceed 170 °/170 °. And again, these numbers are mostly optimistic. Still, for many common uses, it is an unimportant criterion, unless your screen is elevated.

Response time

The response time of the slab is a parameter often subject to controversy. It measures in milliseconds the speed of change of state ("extinguishing-switching-off") of the liquid crystals composing the slab. For simplicity, it is the response time "black to black".

However, it is not uncommon for manufacturers to use a response time corresponding to the "gray to gray" cycle, which is considered more realistic, but also more flattering because it is shorter. If you want to differentiate two screens on this basis, be sure to take comparable values.

The "fastest" PC screens have a response time of 1 to 5 ms, which can be further improved by the technique of "overdrive" (increase of voltage to excite more liquid crystals). That's what you need if you play action games with fast-paced footage, or watch movies. Otherwise, you may see persistent images or ghost trails that will spoil your experience. For all other uses (office automation, image editing ...), it is not an element of crucial importance.

The display frequency is the number of frames per second, evaluated in Hertz (Hz), displayed by the monitor. It was a very sensitive parameter at the time when CRT monitors prevailed and an unpleasant flicker appeared when the frequency fell below 60-65 Hz.

Due to their response time, LCD monitor slabs are not disabled by this phenomenon unless the brightness is set below a certain threshold (see Flicker-free technology in Chapter 6). Thus, the vast majority has a frequency of 50 to 60 Hz and the image is of a foolproof stability.

Color reproduction

It is dependent on two elements:

The color space, also called "Gamut" is the range of colors that the screen can display. It is expressed as a percentage of the sRGB (or sRGB in English) or Adobe RGB space. This allows you to display more colors, including some very saturated colors. But it is only sensible in a professional context, for a graphic designer for example, who uses Photoshop and who wishes a total respect of the colors in the chain of treatment of the image.

Color accuracy: The majority of PC displays display 3x8-bit color coding (one channel for each primary color: red, green and blue), which represents more than 16 million reproducible colors. The most advanced models display more than 1 billion, thanks to a 3x10 bit coding. Again, only image professionals will benefit, provided they put in place all the tools to work in 10 bits including the graphics card (Pro FirePro AMD or Quadra nVidia range).

The colors of professional screens dedicated to image processing are generally calibrated at the factory, so that their reproduction is faithful to reality. If this is not the case, the acquisition of a colorimetric probe is necessary.

Different display technologies

For the computer screen, several technologies of LCD slabs coexist, the shades being housed in the electronics and the structure of the matrix of liquid crystals. Each has different physical characteristics and inevitably compromises. Their strengths and weaknesses are described below.

TN (Twisted Nematics), economical and responsive

It is the most widespread and economical technology, with 22-inch screens available at around € 100. Its excellent responsiveness (a slow response time that tends to the millisecond) is its main strength. In contrast, the viewing angle is quite narrow and the contrast is medium. As for the colorimetry, it varies from 18 to 30 bits, the 24-bit slabs (3x8 bits, ie 16 million colors) being the most widespread.

Choose a TN panel if you only practice common activities (video games, office, Internet), for which colorimetry and contrast are not cardinal virtues.

IPS (In-Plane Switching) and PLS, ideal for beautiful images

 PA279Q Asus

The Asus PA279Q is a 27-inch screen that combines an IPS panel with a definition of 2560x1440 pixels. Perfect for lovers of image editing.

Related: Best 27 Inch Monitors under $300 on the Market

The IPS is on the rise. Previously expensive, this technology is now entering inexpensive screens, at less than 130 €. It excels in color reproduction and offers an excellent viewing angle. The contrast is also of a good level. The response time, long pointed in comparison to TN tiles, has improved a lot and is no longer a brake for gamers. References under 5 ms are legion.

There are several variants of the IPS: E-IPS, P-IPS, H-IPS, AH-IPS ... Each enhances one or more properties: color reproduction on a 30-bit scale for the P-IPS, time response time of 5ms for E-IPS, better contrast for H-IPS, improved colorimetry and lower power consumption for AH-IPS ... Samsung, for its part, has developed PLS (Plane to Line Switching) technology, cousin of the IPS, with lower production costs.