Using the dual LED flash as a torch may well suck your battery and may well get the LEDs too hot and kill them, I suspect that they are being driven past their normal operating voltage/current to output such a bright light.
I also suspect it will be difficult to get them to stay on in a software program as Nokia probably doesn't like you to use them like this.

As an interim solution I suggest:
Why don't you open the browser in fullscreen and go to a blank page.
You could do this with a bookmark.
It won't exactly light your way but it might help you find the lock to get your key in the door.

If you really want to see in the dark may I suggest you get a Petzl LED headtorch. I always have one in my jacket pocket, very useful on a dark winters night, bright, small, virtually indistructable (even been underwater with it) and batterys last forever.