If you recently bought a 21,5-inch iMac and have had problems with your computer's brightness, it may be time to fix them, as Apple has released the Display Brightness Update 1.0 for the 21,5-inch iMac.
Last month Apple acknowledged the problem and informed its customers that it would release an update to solve it.But it wasn't until quite recently that Apple introduced that much-needed update.
It weighs less than 400 Kb and is applied on Mac OS X Snow Leopard 10.6.4, so update if you haven't.