Some monitors use Pulse Width Modulation (PWM) to control the duty cycle for backlight brightness. If the frequency is too low this can result in screen flicker as brightness is lowered. Some people are more sensitive to this effect than others. A list of flicker-free monitors that don't use PWM is on TFT Central.
For Windows use ClearType to adjust the clarity of text. On Windows XP visit this site. For Windows 7 and later run command "cleartype". Choose selections that minimize color fringing and offer good contrast.