TV guide: What must I look out for when buying a plasma or LCD TV?
Von Simon Blohm, Denis Freund und Reinold Növermann
Translation by Siobhán Hayes
For starters: contrary to popular opinion, there is hardly any "too big" where this topic is concerned. Ultimately, your wallet, space available and player devices will determine what screen size you purchase.
SD material, such as conventional PAL television, can also look well if some basic rules are adhered to; these rules will be outlined below.
An excellent contrast is especially important for flat screen TVs, since the human eye responds very sensibly to contrast and images that are low in contrast look emotionless and flat. In order to measure up in this regard, the contrast of the plasma or LCD panel used should already look good in the factory settings, so that only minimal changes must be made if necessary.
The value should be at least 800:1 and indicates how great the difference in brightness is between a black and a white pixel. The higher, the better. In order to be able to control the contrast of the screen, you should bring what is known as a test disc with you when buying a television. Normally, such a CD contains various grey gradient images, chess board patterns, real test photos and more.
Caution, dynamic cases!
If you rely on the details advertised in the brochure when buying a television, you will soon be in for a letdown. This is because LCD and plasma TVs are often advertised only with their dynamic contrasts. Here, colours and brightness of the image being displayed are adjusted continually by the television and in the ideal case, a very high contrast value can be achieved. However, unfortunately, it is a very theoretical value, which is generally achieved when changing from a very dark scene to a very bright one.
Unlike static contrast, the measurement of the dynamic contrast does not refer to a static image but always to the comparison of two images or scenes following each other. Therefore, take a glance at the manufacturer’s details and then ask the salesperson what the static contrast of the model is. The highest dynamic contrast is little use if the corrections cause the colours to look unnatural or if details in dark scenes are hardly recognisable.
How black is black?
The black value of a flat screen TV can best be tested in a darkened room. Because of the necessary backlight, black in most LCD TVs with conventional backlight always looks a little brighter than on plasma screens.
Samsung F9 series with LED backlight. (Photo: Samsung)
At the IFA 2007, Samsung presented the models in the F9 series (52 and 70 inches) , a new range with LED backlights which is therefore based on light-emitting diodes instead of fluorescent tubes (CCFLs). Whilst an LED backlight in itself offers no real advantage as compared with the conventional CCFL solution, the "local dimming" function here is of importance. The LEDs are divided into many small zones which can be regulated separately to the image content in brightness. This allows the black value to be increased dramatically in LCD TVs.
Relevant models are still very expensive; in the next few months, Sony also intends to follow with LED illuminated flat screen TVs and Samsung is also already planning the successor for the F9 series.
In the lighting in the large electronic markets, which is as bright as daylight, it is unfortunately almost impossible to test the black value. Therefore, it is especially important to look for a high static contrast.
An even image brightness is especially important in dark scenes; if the corners of the image or the top and bottom of the screen are illuminated unevenly or if the backlight shines through, viewing pleasure suffers. Bright or darker patches should never appear on the screen.
In addition, the image brightness must also be sufficiently high to ensure that the image still remains recognisable when strong light such as sunlight falls onto the screen. Some models offer automatic regulation of the brightness with the aid of a sensor. This is not only convenient, but also saves energy.
Small milliseconds and large viewing angles
The response time of a flat screen television is also of fundamental meaning, since otherwise the image looks pulpy when you are watching football, or tennis balls become similar to small comets with tails.
Most current models are sufficiently fast and streaks are largely a thing of the past. The response time of a modern flat screen TV should be less than 12 ms.
Only with smaller models should you ask about the type of panel before buying: if a TN panel is integrated into the model, you must expect limitations, especially in the vertical viewing angle. If you then wanted to hang the television and look onto the screen from below, you will often see only a negative image.