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Introduction to high-end PC displays

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There are several types of monitors, with the TFT displays being the most important. We regard the CRT (Cathode Ray Tube) based displays as obsolete. Moreover, plasma displays don't suit computer based systems very well (due to their problem with static images; they tend to "burn into the glass"). Consequently, the huge numbers of displays on the PC market are TFT based types. We will, therefore, only consider these display systems.

TFT concept

The inner workings of TFT screens are based on LCD (Liquid Cristal Display) technology and can be understood by looking at the following figure. First, white light is emitted from a flat light source. The presence of a light source in a TFT display can be seen from the fact that it does indeed give out a lot of light. Next, this light is polarized horizontally by a filter. The third stage is a grid of liquid crystals that can change the polarization of the light to vertical. Each crystal corresponds to a pixel. When the polarization is not altered, the horizontal polarized light cannot get past the last polarization filter with its vertical orientation (black pixel). When the crystal alters the polarization vertically, the light will pass through it (white pixel). Now we have a black/white display. To add color, every pixel is divided into three sub-pixels, each with a primary color, realized by a color filter.

There are some important things to consider when looking for a TFT display. Let's take a look at the issues.

LCD explained

LED technology

The light source in a TFT display was always realized by using several TL lights. Nowadays, however, these TLs are increasingly being replaced by LEDs. LEDs use much less power and, when using a lot of them, you can form a ‘grid’ of LEDs which can, in turn, be adjusted to the light intensity required by the image. In this way, the darkness of the display becomes much better (by turning down the intensity level in that region), with a better contrast ratio as a result. The pixels themselves again use the same liquid crystal technology as before.

Response time

One of the most critical tasks that the display must deal with is responses, without any noticeable delay, to changes in each successive frame. This is defined by the time it takes to change the color of a pixel and is measured in milliseconds. For simulation and gaming, this is probably one of the most important issues and should be five ms or less. Unfortunately, not all manufacturers use the same methods and definitions to measure and specify response times. So, the values must either be interpreted or you should test the screen before buying. There is also some good news in terms of the low response time requirement. It means that the displays without all kinds of sophisticated image enhancing technology are better suited to our purpose.

Size and resolution

The display size is measured diagonally. The size needed depends on the particular set-up you have in mind. A 22 inch display is commonly used. These often have a resolution of 1680 x1050 or 1920 x1080 pixels (the latter being full HD resolution). The term resolution is somewhat confusing. Theoretically, it should be expressed as the number of pixels per inch. In practice, however, it is nearly always used as an indication of the total number of pixels along the horizontal and vertical axes. In general, the larger the display, the more pixels you get (note that the number of pixels per inch doesn't change). Be aware that the number of pixels is not only an indication of resolution, but is also an indication of the computer power required! A (TFT) display should be driven with this native resolution, or it has to scale the received image up or down, which takes time, again resulting in poor response times.

Contrast

Contrast is defined as the ratio between the brightest and darkest colors; in other words, the ratio between white and black. Higher values are preferable and create a sensation of deeper colors. Good quality displays have a static contrast ratio of around 1000:1 or better.

Luminance

Luminance describes the brightness of the screen. Its value must be aligned with the light conditions in which the displays are to be used. Normal values are around 300 cd/m2. Higher values are only necessary when, for example, the screen is to be used outside (daylight conditions), which is not the case for our purposes.

Connector types

TFT displays are digital devices by design and should ideally use DVI or HDMI connectors. Analogue interfaces are also common place (VGA type). The connector should match the type of graphics card in your system or a has to be used.

VGA connector  HDMI connector  DVI pinouts  DiplayPort

Miscellaneous

Other things to consider are color and speakers. So far as the latter is concerned, the best solution is to use a separate speaker set. The quality of such equipment is much better than that used in a display. Also, when using two or more screens, the speakers are no longer utilized. Colors should match your personal taste and /or the color scheme of a simulator mock-up.

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HeliStart is authored by Peter Goossens.


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