This seminar discusses the impact of a light source in six dimensions: Safety, Preference, Energy Consumption, Environmental Impact, Skyglow and User Health. Each of the six dimensions have a different level of importance based on the roadway type and the area surrounding the road. Similarly, the selection of the light level, light source spectrum and approach to adaptive lighting are all linked by performance to each of the dimensions investigated. As new data becomes available, including recent studies from the Department of Energy, the Federal Highway Administration and state roadway agencies are providing a clearer picture of how lighting impacts each of these dimensions, both positive and negative. Once the impacts are found, an approach to selecting the lighting specification is possible where the tradeoffs between impact and importance in each of the dimensions can be balanced. Managing this balance allows the roadway agency to approach the ideal light: a light source that maximizes the desired outcomes and minimizes the negative outcomes. This seminar discusses these issues. Examples of newer technologies can enable LED lighting to be used effectively and efficiently in roadway lighting will also be discussed.