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REPORT

Burn-in effects on LCD TVs

By Simon Blohm
Translation by Siobhán Hayes
30.05.2008, 06:31

Those with some technical knowledge and the experts are familiar with the problem. Static images leave traces on screens in unfavourable circumstances. These are silhouettes, similar to photo negatives, which are caused by the burn-in effect or memory effect. These appearances are often referred to as ghost images.

If these burn-in effects were usual in former times with classic computer monitors when screen-savers were not used, modern LCD screens are considerably more resistant to these undesirable silhouettes, but do not exclude the possibility of their arising.

In order to clarify better the physical processes involved with burn-in effects, we shall compare conventional cathode ray screens and the technology used in LCD models.

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Cathode ray screen technology

In television sets and monitors, cathode ray tubes are used which replace electromagnetic deflection systems (deflectors) belonging to the upper group of cathode ray tubes based on their larger viewing angles. Here, they are distinguished from other cathode ray tubes such as x-ray tubes or picture tubes used in oscilloscopes.

The actual screen (the end of the cathode ray tube that is visible to the viewer) is coated with particular minerals and an aluminium layer on the inside. The minerals transmit visible light when they are bombarded with electrons. With colour cathode ray tubes, the inner layer is more complicated in its make-up but follows the same basic principle.

The electromagnetically controlled electron rays are read by the screen, independently of the television norm, line by line in various frequencies and create a visible image through the electricity-dependent glowing of the mineral layer.

Burn-in effects on cathode ray screens

The burn-in effect on cathode ray screens is based on the physical and chemical characteristics of the minerals used. Areas of the layer which are constantly "bombarded" by the electron ray gradually change their characteristics and appear as ghost images which can no longer really be removed. Therefore, it is advisable not to allow static images to be displayed for long periods on classic tube screens.

LCD technology

When it comes to LCD technology, particular crystal particles in a liquid (LCD = liquid crystal display) are found between two glass plates. The transparency of these crystals is controlled with various voltages. The glass plates are illuminated permanently from the sides or from behind. The main advantages of the LCD screen are its flicker-free image, ultra-slim form and very low power consumption. However, production costs and outlay are very high.

LCD technology has now become the most common form of flat screen technology. Although many potential LCD screen users assume that burn-in is not possible with this technology, they are mistaken.

Burn-in effect on LCD televisions

LCD technology is not susceptible to the actual, permanent burn-in effect seen in classic cathode ray models. However, a long-term, obstinate ghost image can also be seen time and again in LCD screens. Menus from DVD players and connected computers and consoles in particular, but also broadcaster logos and video and teletext pages sometimes leave behind an unpleasant and often distracting trace on the otherwise so pleasant screen.

The reason for this is the characteristic of the crystals that leads them to take on new transparency characteristics when they are being used for long periods in certain sections. However, this only occurs after a few hours of "continuous bombardment" in reasonably good models.

The advantage of LCD models as compared with cathode ray models with regard to burn-in effect is that in LCD models, this effect can be prevented fundamentally by technical means or can be reversed.

If TV programmes in 4:3 format are displayed for too long on a widescreen LCD TV set, the black borders at the side could remain on the screen as an unpleasant "memory effect".

Avoiding burn-in effects on LCD models

A burn-in effect often appears on LCD models as a certain lingering illumination and les soften as a truly burned on image effect. Many LCD TVs come with the technology (Pixel-Shift option) to move the image a few millimetres at particular intervals. The movement is not noticeable and this prevents burn-in.

If damage has arisen, image noise often helps to remove ghost images. Simply unplug your aerial and allow the liquid crystals to move about properly for some time so that all crystals can be raised evenly once more.

Alternatively, you can unplug your television for a few hours or a few days for very strong effects in order to achieve a ghost-image-free picture once more.

However, if you would like to protect yourself against using these rather radical methods, you should simply ensure that a burn-in effect can be excluded to the largest extent possible. Te best way to do this is to use all crystals as evenly as possible. For this purpose, modern DVD players come with screen-savers which keep the crystals and there is also the aforementioned Pixel-Shift option.

If you take care of your LCD screen, you do not need to be afraid of the burn-in effect and you can enjoy your modern ultra-slim technology for years to come.

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