It's basically your vision. Include all things relevant to completing it.
This is straight out of the link given, which I hope you read. If not, here:
At some point prior to producing the actual 'lighting design', the designer must form a LIGHTING CONCEPT. Typically, this is a statement of what the designer hopes to achieve with the lighting design, and how he hopes to achieve it. It may be written, or verbal only, but the concept must exist, at the very least in the designers' mind.
The concept should be fundamental. It should capture the intrinsic qualities in the play and relate and describe them in terms of light. If properly developed, the concept will assist the designer with every step of the lighting design process. It will be used constantly to justify the designer's choice of style, lighting methods, directions of light, use of intensity, distribution, color and movement, etc.
Often the concept may become clear after the first meeting with the director and the other designers. At other times, the concept may develop slowly over a period of weeks and may not become evident until the designer has had the opportunity of watching several rehearsals.
The lighting concept is generally based on the emotional qualities developed by the playwright and indicated by the script. The concept will also be influenced by the directors' and the other designers' interpretation of the script. Everyone must be on the same page at the same time, when it comes to the design concept.
The lighting concept may sometimes be as simple as: 'to provide a feeling of warm, muted, sunlight over the entire stage, with a strong dramatic sense of motivation from stage left'.
Often the concept will be far less simplistic and will relate more to the production on various emotional or metaphoric levels. As the designer analyzes the play, he will often find; contrasts, conflicts, juxtapositions, metaphors, symbolism, irony, and other dramatic devices. How he relates these images to the physiological of design, is an important part of the design process, and is usually defined as part of the concept.
Example: A stylized play about a couple that are diametrically opposed to each other and are always fighting - might be seen as a 'cat and mouse game'. So the designer will use 'cat and mouse colors' (maybe pink from one side and gray from the other). He may show the contrast between the two characters with contrast in the lighting. The 'cat' may be illuminated with sharp, threatening lighting, while the 'mouse' may be sympathetically illuminated with soft warm light. So every thing regarding choice of intensity, color, direction and movement of light, can all be justified by the concept.
Good lighting can and often does exist, without a concept. However, the lighting designer that takes time to develop a strong overall concept is ultimately better equipped to make rapid design decisions, as there is now complete justification and direction for all of his choices.
