Tone Mapping allows us to map certain light energy which is beyond the viewable range to a viewable range. Although not completely useful for this scene, we initially thought that it will allow us to control the luminance of certain regions near the lights which are over-exposed.
The method used is the one described in the paper by Drago et al. This method gives a bias variable which allows us to control how strong the effect is. Values farther away from 0.5 means more intense the tone mapping.