I get a lot of milage by setting up an object's materials like this, below, and then adjusting Emission, Color, and especially EmissionStrength. Also following is an example of using this for getting light from a Wall Lamp. You can get a starting setup by copying it from the Wall Lamp (looks like this one!) and editing its materials. You'd probably want EmissionStrength a lot lower. Oh, and make sure that the Properties of object has Light Emitter checked.