When you do the levada hikes on Madeira, you should check out the route before you go. When they mean good flash light they mean good flash light and that is what they say. Do it.
The batteries in our headlamps were relatively low and we had to change the batteries to get more power.
Without good light you do not see the wall or the ceiling that keep jumping in your way. Needless to say that the path goes along the levada edge a lot. Result: small balcony to walk on. With a side wall on one side that is all uneaven. And with a wall on the other side that is out of reach. But with a water edge you should not fall into.
We thought it was fun and a little adventurous. Some of the tunnels you were walking through for 15 minutes or longer.
Have a look at what the tunnel end looks like. The light reaches in for a few meters only. Then it is virutally dark.