When light hits a surface, it will either be reflected or absorbed depending on the colour it meets. White surfaces reflect the entire spectre of light, while black surfaces absorb it instead. Knowing how surfaces respond to lighting will help you strategically place light sources depending on the effect you want and the function they serve.
Because white walls reflect light, they are ideal for illuminating a room and making it optically larger. You can create a calm and indirect light by pointing the light towards the wall with a dull surface; a blank surface could blind people. Always go for adjustable lights as they will help you control the direction of the light and the spread.