the 170/180 used two different manufacturers on the LCD panels themselves. 

one of them is really bad for tunnelvision. they all do it.

2nd one has a more white backlight and matches that of the macintosh portable backlit 5126 model. they are much better. i have only seen 1 go tunnelvision. you can tell the difference when off. the good one is more gray/white. Bad is more yellow/amber.

my 180 has tunnelvision when the screen is black but it doesnt affect the image. strangely enough.

cool thing is, a 140 LCD/Cable assembly will fit in a 170 and work. you just lose active matrix.