Question about backlight, laptop close, and sleep

Hi! I'm new to these forums (lurked here forever though) and whenever I had a problem, there was always some solution here. My question this time isn't exactly a problem, really - but I can't stop wondering. When I close my laptop, one of two things happen. Either the backlight gradually fades away (the apple logo light) or it clicks off immediately. When the former happens, I can flip the computer back up immediately and sometimes it's like the laptop forgot I ever closed it; I can use it without it falling asleep. Other times I'm online and it falls asleep on me randomly.

Any ideas as to why two different things happen? I'm really curious.

No - well, the main question is, when I flip my laptop closed, the backlight either instantly clicks off or fades away, always one or the other, and both happen whether I'm plugged in or not. Laptops I see at the Apple store never "instantly click off" their lights - all of them do the fadey thing, but mine also does the instant clicky thing, and I want to know if it happens to anyone else and if there's an explanation.

No magnetic items nearby. When I say it falls asleep during use, I mean specifically that when my laptop does do that fadey thing when I close it, I can bounce the hinge right back up and the display will turn right back on instead of sleeping, and then I can use the laptop as normal. But sometimes when I try that, I use the laptop as normal for a little while and it goes back to sleep.

My keyboard backlight is always off, incidentally. Also it's a macbook air 2012 13in base model + 8gb ram