given that OP's story is that he WAS terrified, do you think that would make him more likely to turn them on than your clearly hard as nails grin DH?
The thing about turning a light on early on, is that it means any intruder can see you too.
These are just random thoughts, but you know the layout of your house, and are substantially better at navigating that than an intruder (assuming they haven't been there a number of times). If you turn on a light, you lose all that advantage.
But that's not necessarily relevant to the case here. I'm just saying, I can see why people instinctively keep the light off.
Actually, I remember a brilliant episode of 911 or somesuch US reality cop show. The 911 call was a terrified woman, cowering in her cloakroom, because she'd come home and found an intruder in the hallway. She was whispering in the phone replay, and deliberately kept the light off so she could hide. The police came in, called out, flashed a torch around, and discovered the dressmaker's mannequin that her mother had dropped around. They said she did exactly the right thing, and these things happen, so it's perhaps not that unusual, and perhaps there is an instinct to hide in the dark.
What I will say is that I find it utterly bizarre that the lights were still off at the point he's looking for his socks. I can't work out why he'd do that at all.
And, coming back to the intruder/layout of the house thing, given that Reeva hadn't stayed there all that often, I find it utterly bizarre that she didn't turn the bathroom light on, given that she didn't know the layout as well, and she had seen that Pistorius was already awake.
Stupid a point as this might seem, but I'd really like to know where the bathroom lightswitch was. How many times would one or the other of them have to walk past without turning it on? If it's on the passage wall, then the amount of time OP says it was dark is just strange. I can see it if the bathroom light is out by the bedroom door.