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Review: Hercules ProphetView 920 PRO

by Ryszard Sommefeldt on 5 November 2003, 00:00

Tags: Hercules Prophetview 920 PRO, Hercules

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How Do They Work?

Before I get on to the specifics of Hercules' monitor, a quick piece on how LCD monitors work. Mainly for my benefit, since I was clueless about how they worked until recently, hopefully you'll pick up something too.

An LCD monitor uses liquid crystal to display your picture. Liquid crystals, chemicals that have crystal-like properties when interacting with light, switch state depending on certain conditions. The very first discovered liquid crystals, found back in the late 1800's, changed state depending on heat. Today's versions change state depending on voltage.

To display your image, the first building blocks of a flat panel monitor are a light source. The light passes through the LCD to your eyes, so you can see it. Early implementations used a single neon lamp to provide the light source, but current models often use 2 or 4 (in a 2 x 2 matrix) instead. With the lamps having limited life span, the more the better. In a 2 lamp setup, one will usually cut in when the other dies out, doubling the effective lifespan. Variations on that theme include using 2 lamps concurrently for the same average lifespan, but better overall brightness, and 2 sets of 2 lamps to provide the best of both worlds.

Given a light source, the next main feature of the monitor is the LCD setup itself, used to create your image. The LCD panel is made of LCD subpixels, single pixels split up into their constituent red, green and blue components and arranged in a strict array. The subpixel array (native resolution x 3 subpixels) is covered on both sides by an RGB filter that lets light pass through it. Each subpixel group (single pixel) is controlled by an individual transitor with the actual displayed colour of the subpixel controlled by a highly accurate, variable voltage applied by the transistor. The voltage applied to a subpixel group causes it to refract the light from the neon source which then passes through the RGB filter and out to your eyes.

The refractive properties of the subpixel group, along with the switching time of the transistor that controls it, makes up the bulk of the performance in a flat panel monitor that people care about. The quicker a subpixel group can change colour from one extreme (pure black) to another (pure white), the quicker it can refresh an entire image. The faster it can do that, the more frames per second can be displayed by the monitor.

It's this (sub)pixel reponse time that garners most press on a flat panel LCD display these days. Consumers need to know how fast their pixels can refresh an image, to determine if they are suitable for use when playing games or displaying other fast moving images. Slow pixel refresh means subtle (or not so subtle) ghosting, where the previous displayed image can still be seen on the monitor, as the monitor refreshes the pixel array to display the next one.

Even more so, it's pixel response over the entire colour range a pixel or subpixel group can display, that determines the performance of a monitor in terms of being able to display a fast moving image. Certain recent 16ms pixel refresh panels have only been 16ms across a subset of colours that the subpixel group can possibly display. With the colour range for that 16ms time being the most 'popular' colours displayed by a pixel, it can be 16ms for the majority of the time, but often is 20 or 25ms for the full colour range. Obviously, colour change can be done very quickly if the new colour is right next to the old one in the colour spectrum, so testing panels switching from black to white is the optimum method of testing.

That's the basics of how an LCD monitor works, without going into too much detail. The electronics and power of the neon lamps controls things like brightness range, colour temperatures, auto correction and contrast. I'll cover those things when necessary in further pages.