Many of us remember when the internet had to be dialled up and when computer screens were housed in a giant box. It’s likely that children born today will be using computers far more advanced than we can imagine, and wouldn’t even recognise the computers of 10 years ago. The hi resolution, LCD screens we use now have come a long way from their humble origins of 50 years ago.
Cathode Ray Tubes (CRT)
The longest used form of display monitor is without doubt the CRT (cathode ray tube). Here, a tube containing a vacuum holds three electron guns. At the narrow end of the tube, each electron gun has an anode and a cathode assembly. The cathodes emit electrons, whilst the anodes draw the electrons away, which forces them to accelerate and become electron beams. These beams get fired at the back of a screen, covered in phosphor dots. As the beams hit these dots, they glow either red, green or blue (RGB). The guns fire down the screen, horizontally, varying in intensity to manipulate the glow and create an image on the front of the screen. Despite producing crisp, clear images, CRT monitors are incredibly bulky, and producing a larger image means increasing the size of the tube - and hence the size of the monitor.
To combat this drawback of CRT screens, a flat panel display monitor was developed - the plasma display. Plasma works in a similar way to CRT, in that small fluorescent lights are illuminated at different intensities to produce an overall image in a full range of colour. However, rather than using the cumbersome cathode tubes, this time a plasma gas is used, xenon or neon. When an electrical current is run through these gases, the particles crash into each other and release photons of energy. Only thin materials are needed in order for this process to occur, meaning that plasma screens can create clear images, without a bulky monitor. However, the technology is expensive, and the image quality is not quite as good as the best CRT sets.
Liquid Crystal Display (LCD)
Many of us are most familiar with LCD screens. Almost all electronic devices use LCD displays, including our computers, laptops and even microwaves and digital watches. LCD screens use the process of polarising light to switch pixels on or off. It is a fairly complex process, involving semi solid crystals, called nematic liquid crystals. In an LCD screen, linear polarisers either allow light to pass through, or stop light from passing through a filter. The crystals are lined up like small, thin rods and move together when a voltage is passed through them. It is this interplay of polarised light and multiple voltage currents that forms the images on our screens. It is a technology very different to CRT and plasma, and provides us with excellent resolution. LCD screens take up very little room, and it is why we are able to have the thin laptop and computer screens we are now so used to. Less bulky than CRT, and cheaper and more powerful than plasma, it seems that LCD displays are here to stay.