lost screen but backlight is on

My macbook air 11" of late 2013 would suddenly go dark while I was using it. However, keyboard light and screen backlight were still on (I could see the bright Apple logo on the lid). Nothing I could do to revive the screen except to power cycle it. I called Apple support and they determined it a hardware issue and got me a brand new Macbook Air from the store.

Now the second MBA has just displayed exactly the same symdrome, (with the slight difference that keyboard light went out also initially, then came back after a minute or so) which lead me to believe it is not hardware problem. As far as I remember, applications running at that time were Safari, Finder, Numbers, Pages, Messages, Mail, Calendar and Dashboard, all Apple programs.

Has anyone experienced the same problem? Any suggestions?