I had same problem on my Aspire 8920g in 2013. Just want to share my solution.
oldturkey03 is right that the problem is with backlight.
I solved it in two steps. Starting with easiest.
First - replace inverter, in my case the problem was still there, but for some users it can be solution.
Second - replace LCD CCFL Backlight. This step is more difficult, but with patience and skilled hand it is less than 2 hour job. To change CCFL is cheaper than whole screen.
You can find them for under $20, just search eBay for "LCD CCFL Backlight Aspire 8920",
example [http://www.ebay.com/itm/2pcs-18-4-W-LCD-CCFL-Backlight-Lamp-for-Acer-Aspire-8920-8920g-8930-8935-8935G-/360665387649?hash=item53f9551281:g:QD8AAOxyzfNRvCJj|eBay link]
I did this repair in 2013 and still PC is working without problems.