left side of my screen is getting dark
this just started all of a sudden today. Any ideas on a fix?
iMac, OS X Yosemite (10.10.3)
That sounds like failing left side backlight.
Your best bet, is to take it to make an appointment at your Local Apple Store or Apple Authorized Service Provider.
use > https://locate.apple.com/ to find the nearest Service Provider in your area.