You can use a night map and not sacrifice the benefits of a lighter map. If you have your overall light source, that will create more-or-less a flat plane of light for vision (ie, the street lamps). Then, using of point_spot and light_spots you can point out entrances/exits and highlight more important features if your a bit creative with your lighting.
Also, subtle adjustments in the lighting color can help too. Those street lamps should eventually give off a bit of a yellow light (like a brown bulb) where as a spot light would be more closer to white. When the white is shown on the yellow, it'll easily highlight whatever is needed.