Add lights in other places?

Yes, it is going to be dark without lights.. That's how world works. If there are no light source, it will be dark.

K. I won't.

You're using lightenvironment the wrong way then. Lightenvironment works as sky light. If you have properly used skytextures and added the light_environment in the map with correct parameters, you'll have nice light. Of course, if you make a dark light (low light) value adding normal to specific places with specific parameters could make just that place under the light post look like the light of the lamp post without affecting the whole map. I suggest you start looking up tutorials but don't copy what they say to do literally. Try to learn how lighting works in Source.

... dont listen to them.

The reason your map becomes all dark when you add the light environment is because you have not added the skybox texture, secondly the ambient light settings are more then likely on default, 20. change this number to 80+ this will bring the shadows out of the dark.