60hz vs 75hz+

[Goodwin]

I know that for CRT screens, you need ideally 72hz, or 75hz and up for flicker free. For LCDs, it's 60hz. Why is it the hz can be lower without causing eye strain?

[UnknownSouljer]

It has to do with the how CRT's and LCD's render the image.
Hz rate matters significantly more on CRT's because it has to draw every pixel on the monitor with a single electron gun repeatedly. This single gun must continually draw the image. With low refresh rate, it causes strain on the eyes because of flicker.

LCD's have individual pixels that show the image on the screen continuously. They don't need to 'refresh' or 'redraw' the image if whatever is on the screen doesn't change.
Hz rating for the most part doesn't matter on LCD's. If you're looking for a 'fast' LCD you should be looking at input lag, pixel rising and falling time, overdrive, and what type of panel it is (ex: PVA, MVA, IPS, TN etc.)

For more basic things about monitors, I would recommend you read the wiki articles based on them. Tons of good information.
http://en.wikipedia.org/wiki/TFT_LCD

[Stinus]

Off topic, my co-worker always leaves the default for his CRT, which I know is 60 since it flickers so much. I have no idea how he puts up with it, but it's murder on my eyes when I pass by.