I'll make sure to add arrow key support.
Can you tell me what settings you were playing at? (I'm wondering what made the tutorial area so dark)
As you can see on my screenshot below, I was standing on that platform and couldn't see the target at all... had to search for a while...
! Keep in mind, the player is always attracted to light. Putting a big white tree there was a good idea but also the reason why I missed the platforms in my first playthrough. ^^ So if you want to guide the player to a location, just put a light there.
There were some unintended side effects with the brightness slider so it's disabled in the 1.31 build. As for the tutorial, it's okay if people are looking for a while, it's very empty, eventually you'll spot the target.
As for the cave, I agree that it's dark. That's why we added the torch you can equip by pressing T. (see lower right bottom/tutorial message)
Caves are still somewhat affected by the time of day outside which is unintended but the caves in game will be dark. That's why we added the torch. I hope to fix the brightness slider for the next build.
Luckily most people are in fact guided by the big god rays and lights placed around in the cave which do lead to the exit, like you said, players follow the lights ;)