Realistic lighting (sunlight) with Three.js?

I'm attempting to create a small 1st-person game using Three.js, but I'm having trouble with the lighting. Basically I want to simulate the sun and have it rotate around casting light on everything. I'm using THREE.DirectionalLight at the moment and it only lights up the one direction so sides of cubes remain black/dark.

Do I have to use multiple lights so everything is lit up? Or could I somehow reflect light off the ground/objects?