Also,
- Open the map.
- Select a brush that is not a part of an entity
- Press "n" and you should see that it is a the "worldspawn" entity
- In that window that opened, add "_minlight" the the key field
- Add "15" to the value fileld
- The makes the minimum light level 15 in your map. I found that 15 still allows for good shadows, but makes it so everything is fairly visible. You will still need to add light entities to your map. If you want a brighter looking map like dm_dry, then increase the lighting to 50 or something.