This question has been asked many times. Essentially, a lighting consultant will be qualified enough to address all of the aspects of quality lighting design and specification. This includes safety & security, mood lighting, comfort, acuity, functionality, energy efficiency, client budget considerations, verification of fixture, design prediction, and fixture maintainability. These qualifications are achieved through both education and lighting industry experience.
Lighting consultants use their ability to design with light and paint an infinite palette of mood. This begins with a knowledge of how light works within an environment. Harsh lighting is not suitable for a professional environment, but the kind of lighting you have at home may not suit your office cubicle.
Lighting consultants know all the tools in their toolbox - the best lighting products, how to effectively use them and so on. They stay abreast of current market trends and regulations. Most lighting consultants work together with architects, builders and interior designers. They ensure that a high standard of quality is always achieved in all projects they are involved in. As for existing buildings, they often encounter structural limitations and work to find creative yet functional lighting solutions.