Either increase the power on the spot lights, mess with the range values on the spot lights, or add point lights to create low level ambient lighting.
I don't recommend using spot lights for general purpose lighting.. they are not good at providing smooth levels of illumination without several hours of fine tuning. Use point lights to get things close to where you want them, then save spot lights for creating highlights and making things interesting visually.
Doublecross is an excellent example of spot light use. Foundry is pretty good too.