ADVICE WHEN BUYING A MONITOR

Only a few years ago, there was only one option if you wanted a high quality monitor capable of high resolutions – the bulky CRT. Now the sleeker LCDs are closing in and it’s more a matter of personal preference, budget and space on your desk that determine what type of monitor to buy.

CRT
CRT (Cathode Ray Tube) monitors consist of a vacuum tube containing several elements. In this tube, a cathode ray emits electrons when it’s heated. On the surface of the screen there’s a layer of phosphor, and when the electrons hit this surface, the phosphor lights up, producing a dot of colour. To create all colours, three electron guns (one each for red, green and blue) are needed. If the electron beams are slightly misaligned, the image will appear slightly out of focus and there are different ways to handle this:

Shadow mask
One solution is to use a mask in front of the phosphor-coated surface. The mask is a sheet of metal (usually made of a Nickel/Steel alloy called Invar), with holes drilled in it. Only beams that are correctly aimed will pass through the holes that correspond to the particular phosphor dots. The mask blocks any stray beams from striking the wrong phosphors. The mask takes up a high proportion of the screen, preventing a large amount of electrons, and thus, light, from getting through it.
 
Shadow mask CRTs produce a very sharp image but it’s darker than an aperture grille monitor.

Aperture grille (Trinitron/Diamondtron)
The aperture grille type of CRT has a completely flat screen.
 
Painting phosphor dots on the inside of a tube can be tricky, so another technique was developed; the phosphor is painted in vertical lines. Instead of using a shadow mask, stray electron beans are blocked by very thin wires. The wires that doesn't allow beams to cross, takes up less room than in the previous technology, and this result in images that are clearer and brighter.
 
The disadvantage with this technique is that the mask is made up of thousands of very fine filaments that must be held firmly in place. Therefore, there are two horizontal wires across the screen; that absorb shocks and expansion when the materials heat up to a certain degree. This produces two faint lines that can be seen on the screen against a light background. This can be tiresome for some users, but the eye gets used to it after a while, and has to look hard to see the lines.

Slot Mask
The slot mask is a new hybrid of the shadow mask and the aperture grill, combining the two technologies in an effort to attain only the advantages of each. The Slot Mask has vertical slots like the aperture grille and the firmness of the shadow mask. The brightness is not as great as with Trinitron technologies, but the image gains in stability. Monitors using this technology go by names such as ChromaClear or Flatron, for Flat Tension Mask.

EDP (Enhanced Dot Pitch)
The system is different from Trinitron in that it focuses more on the implementation of the phosphor than the mask or grill.
 
On a shadow mask tube, the three phosphor dots that form a pixel are arranged in an equilateral triangle. This gives even distribution over the entire screen. With the EDP, the distance between the horizontal dots is decreased, so an isosceles triangle forms the pixel. The dots are elliptical, giving better representation of vertical lines, reducing the slight zigzag that appears on a shadow mask monitor.

LCD
LCDs (Liquid crystal display) take up less space on your desk than a CRT monitor, but there are many things to consider.
 
The worst part is that LCD monitors can have dead pixels, pixels that remain white (lit), black (unlit) or coloured, depending on what part of the panel is broken. Some manufacturers have a zero tolerance against defective pixels so you can replace your monitor if it has just one dead pixel, but some require up to eight dead pixels until you can get a replacement. Pixels can be defective at the time of purchase, but can also be destroyed if you press the monitor’s surface with your finger.
 
Flat panel displays have excellent focus and sufficient colour quality for standard office applications such as word processing and spreadsheet calculations, but they are not as suitable for graphics designers who require photorealistic displays. Another concern is the response time that makes them far from ideal when playing fast action games or movies with rapidly changing scenes.
 
Ergonomically, TFTs have a lot to offer: they take up less space on the desk, use less power and have lower emission values.
 
If you buy a LCD monitor, get one with a native resolution that you want to use. Otherwise you will get scaling errors when the ratio between the resolutions is a fraction, making characters appear blocky and distorted.

Technique
One or more neon tubes make up the so-called backlight, which illuminates the display. If there are multiple tubes, they act as a backup in case the first one breaks, extending the working life of the monitor.
 
The light is redirected through a system of reflectors before it reaches the panel. Each pixel is made up of three sub pixels; each controlled by a transistor that generates a voltage that causes the liquid crystals in each sub pixel to move to a particular angle. The angle determines the quantity of light that passes through the sub pixel, which, in turn, creates the image on the panel.

Screen size
With prices dropping on larger screens, there’s really no reason anymore to settle for less than a 17inch CRT or 15 inch LCD. This will in both cases give a visible size of 15 inch, since the CRT has an edge area where no image can be displayed, but it’s still included in the screen size.

Dot pitch
This is the distance between two dots of the same colour. This is generally measured diagonally, but for aperture grille monitors it is sometimes measured horizontally.

Resolution
The most commonly used resolution is 1024x768 for a 17 inch monitor or 1200x1024 for 19 inch monitors. The higher the resolution, the smaller the text and icons will be, so there’s no reason to go to extremes.
 
If you try using a resolution that your monitor can’t handle, that will not only give a lower-quality image; but may also reduce the life of the monitor. On the other hand, if you buy a monitor capable of much higher resolutions than you intend to use, thus running it at lower resolutions can produce moiré patterns and give you less than optimal performance (not to mention the fact that you are also wasting money).

Refresh rate
The number of times an image is displayed in one second is called the refresh rate. It is expressed in Hertz (Hz), so a monitor with a refresh rate of 75 Hz "rewrites" the same image 75 times a second. Note that this rate of 75 Hz is not random, because it is the requisite minimum for a good image with no flickering. While no two people are alike, it is probably best to try and run a CRT monitor at 85Hz or better, in order to reduce eyestrain caused by flicker (even if you can't actually see the flicker at lower frequencies). This only applies to CRT monitors, and is of the same importance as response time for LCDs.

Horizontal frequency
The speed that a monitor draws a single scan line, called the "horizontal frequency," is measured in kilohertz (kHz). The process repeats, painting line after line, until the screen is filled.

Vertical frequency
The speed that a monitor draws an entire screen, called the "vertical refresh rate" or "frequency," is measured in hertz (Hz).

Bandwidth
The bandwidth is the amount of data that a monitor can handle per second. To calculate an estimate of the bandwidth needed for a given resolution and refresh rate, you can use the following formula:
 
Bandwidth = 1.05Y*1.3X*R
 
Where Y is vertical resolution, X is horizontal resolution and R is the refresh rate. That gives an approximate bandwidth of 87MHz for 1024x768@85Hz and 145MHz for 1280x1024@85Hz

Colour depth
Colour depth describes how many colours that can be displayed on a monitor's screen.
 
"True" colour is also called 24-bit colour. Each colour has 256 shades, giving us millions of colours, This is pretty much what's needed for a monitor's colours to look "true" to the human eye.
 
There’s also 16-bit, or "hi" colour, which represents thousands of colours, and most of the time this looks ok, except in areas of subtle shading, like in a sunset photo. Then the lack of a colour depth will show up as banding in the sky.

Pixel response time
Pixel response time is as important when choosing a LCD monitor what refresh rate is for CRTs. The response time is the time, which a TFT cell requires to switch on and switch off. For standard office applications a response time of 70 ms (milliseconds) is sufficient, but for multimedia values under 30 ms are required.
 
Many TFTs still have problems with regard to moving (animated) images. The cause is the response time of the liquid crystals. As the liquid crystals are very slow to respond, fast sequences, e.g. the view from a jet fighter flying through a valley or the credit banner of a film appear to be smudged.

Contrast
Contrast is measured as the ratio between the light intensity of the brightest and the darkest point of an image. High contrast values improve readability and ergonomics.
 
The contrast for CRTs can go as high as 700:1. This is equal to the best LCDs, but the majority have much lower contrast, some even as low as 300:1. Too low contrast ratios cause darker shades to be displayed as black.
 
For CRTs, a high contrast is accomplished by not lighting up parts of the phosphor, while LCDs have to block out the light where darkness is wanted. This is physically impossible as some light always slips through. However, it is physically not possible to do this perfectly - some light will always seep through.

Brightness
Brightness is the emitted luminous power over a specified area. Brightness is another point, on which LCD monitors are superior to CRT devices. Traditional monitors create approximately 80 to 100 cd/m² (candela per meter square). For LCDs, values below 200 cm/m² are not acceptable.

Viewing angle
The viewing angle is the angle from the centre of the image where you can still see the image. Ergonomic requirements are at least 120 degrees horizontally and 90 degrees vertically, and more is better. If you look at the display from a steep side angle, it may look dark or have colour distortion.

Video connections
The standard analogue connector is called D-sub. There are also different digital connectors, DVI-I and DVI-D. DVI–I can be used for both analogue and digital signals, while DVI-D is digital only with a higher data transfer rate.

USB hub
With an USB-hub in your monitor you can easily plug in new devices such as scanners and memory card readers without having to crawl under your desk to reach the USB-connections on your computer.

Colour
A white or grey monitor will be less straining to your eyes than a black one. This is also the reason why black monitors only bear the TCO ’95 marking even though their white cousins are awarded TCO ’99.

Inbuilt speakers
Generally the speakers inbuilt in monitors are very basic with only a couple of watts per channel, so they’re not something you’d want to listen to high quality CDs or DVDs on, but could prove handy if you just want to listen to streamed radio over the internet and don’t have any other speakers set up with your computer.

TCO 95/99/03
The TCO standard covers visual comfort, recycling, low use of chemical components (like CFC). TCO99 also add a minimum refresh rate of 85 Hz.

User controls
With various user controls you can set the monitor up just as you prefer it. Adjusting contrast/brightness or geometry are the most common options available.

After the purchase
When you’ve bought your monitor, it’s good to calibrate it, using one of the excellent monitor adjustment programs there are, available for download from BenchmarkHQ. Normally, only very slight adjustments need to be made, but it’s always nice to feel you’re getting the most out of your monitor.
 
When starting the adjustment, the first step is setting the brightness and contrast levels properly. Brightness actually adjusts the black levels of the CRT, while contrast adjusts the maximum white levels. Higher contrast will make things seem sharper and brighter, while lower contrast gives you more shades ,at a cost of 'smoothing' the image and losing a bit of brightness. You want to have a contrast ratio where you see as many shades of grey as possible, while still keeping white look white and black look black.
 
Most people tend to run their monitors (and TV sets) a little too 'hot,' since brighter seems to look better (particularly in an office environment, with lots of lights and windows). If you max the brightness and contrast settings, you won't get the best picture and you also shorten the life of the monitor (monitors should last at least three years).