What type of monitor? Reducing brightness has been said to reduce eye strain, but i tend to find that i end up straining to read stuff on my screen if i lower it too much. The flickering of old CRT screens can also make your eyes hurt, but newer ones dont tend to have that issue, increasing the refresh rate on the monitor can also help to fix that issue.
Some people get wicked headaches even with LCD screens. Everyone is different, but on CRT's refresh rates above 70Hz will mitigate the chances of discomfort. level of resolution will be a factor in ones ability to read text. Of course the individuals eye sight is a major factor. If you have had eye strain / headache problems simply changing the monitor may not change anything. Try to determine WHY your current setup is causing problems. First place I would look would be to teh current resolution and refresh rates.
Are you worrying about an old monitor you already had for a long time or a new one? Well, if it still hurts your eyes after a month of use, you have a problem. Can't help here.
But if it is your new monitor that bothers you, try using it for a week or so. I recently got a new 21,5" Alienware and the first days it hurt my eyes even after 15 minutes. But after a week of use (and some heavy gaming ) I forgot about all the issues. So sometimes it does take time to get used to a new bigger, brighter screen. Try to play around with brightness also - some monitors come with brightness set at 100 or 70 or 50%, when I need only 20 or 25%. And try turning off dynamic contrast if you have it. My eyes get tired from it for example.
According to my company's handbook on How to Use a Computer Without Going Crippled, Bald or Blind , the monitor should be used with a medium brightness setting in a well-lit room, placed so that the center of the monitor is at or slightly below your eye level, and at least 2-1/2 ft. away. Plus you should look out the window every 15-20 minutes (if you have one in your office) so as to alternate between close-up and distance vision (i.e., relax the focusing lens muscles).
If you are in a cubicle I guess you should get up and ogle the babe across the room instead .
Finally, if using Windows XP make sure you have Cleartype turned on.
yup i agree with u, i use a 32in lcd tv and i turned the backlight down to 1 and now its perfect with a dim light behind the screen and i sit about 4 feet a way from it problem is now i need to buy another lcd to use as a tv