# Usability for Nerds/Hardware/Screen

Computer screens should be so bright that they are easy to read, but not so bright that they irritate the eyes. The brightness should be easily adjustable. The refresh rate should be so high that there is no visible flickering, even when the screen or the user's eye is moving.
A screen should be placed so that there is not too much light from behind and that reflexes are avoided.
Dark text on a light background makes it easier to distinguish small details, but a very bright background is fatiguing to the eyes. A too bright white background should therefore be avoided. A light text on a dark background is more comfortable to read. A text that is distinguished from the background only by color is difficult to read. There must be a difference in luminance as well.
A high resolution is useful when showing graphics or video. Unfortunately, many systems make objects smaller when the resolution is increased. The user should be able to adjust the size of text, icons and other objects independently of the resolution. The developer may think that small text and icons are easy to see, but this may not be the case to the user if the user has a smaller screen, disturbing reflexes, or reduced vision. The vision of many people is reduced when they get older.
Sometimes, it takes a while to retrieve and draw all the objects necessary to render a screen image, especially for web browsers. It is common to show part of the image while waiting for the remaining items. However, there is a problem if the image is re-rendered after the user has seen a preliminary image. If items on the screen are moved around a fraction of a second before the user clicks on something, then the user may inadvertently be clicking on something else. It is also annoying if the screen is re-rendered while the user is filling out a form so that the input is lost or messed up. The best solution is if the sizes of the missing objects can be specified so that nothing needs to be moved or re-drawn later when these objects are retrieved.
From the perspective of health considerations, especially when you happen to work with computers a lot, backlighting of LCD displays may be ranged in the following way (LED and plasma panels are out of the question - they have inherent flickering due to disadvantages and specific features of the technology used in their production):
1) Incandescent backlighting - may be achieved using conventional or halogen lamps, they have no harmful effect related to flickering at all, their spectrum is the most beneficial for your eyes, but they have higher energy consumption (usually 5x or higher than fluorescent tubes), lower lifetime (do not be mistaken by industry claims of a few thousands of hours - those are cost-efficient solutions, cheap and worse ones, the best halogen lamps may have lifetime of about 20000 hours, about 2 years of uninterruptable functioning), and reduced final color reproduction - due to disadvantages of LCD technology, not the lamps. Unfortunately, in 2015 there are no mass-produced professional LCD displays of such kind, though the existing ones may be modded with warranty loss to use incandescent backlighting.
2) Fluorescent tubes - they have inherent flickering due to high-frequency modulation of the current used to power them, but it is mostly negated by their afterglow, so that the resulting flickering is usually unnoticable at their maximum output (which means that you have to put your average monitor with fluorescent tube backlighting at maximum brightness to reduce the flickering to the maximum). They may be modded to give almost constant, non-flickering output (corona discharge), but in such case their lifetime and light uniformity will be greatly reduced. They have better energy saving performance, and average lifetime (compared to short one of halogen lamps), moderate spectrum uniformity and color output.
3) LED backlighting - generally it should be avoided for health considerations, when health considerations are the top priority, they have inherent flickering problems, far worse than fluorescent tubes (due to very low afterglow and PWM used). They are though more durable, may give worse spectrum, but better color output, and recent models have better energy saving indicators as well. Some circuits and better LEDs, PWM-free, may give them 2nd place instead though.
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