Which lighting instrument serves as the main source of illumination for a performance?

The key light is the primary source of illumination for a performance. It is typically the brightest light and is often positioned in front of the subject or performer to highlight their features and create a focal point on stage. The key light sets the overall mood and atmosphere, establishing the primary illumination for the scene and drawing the audience's attention to where it is needed most.

Other lighting types, while important for achieving depth and balance in the overall lighting design, serve different functions. Fill light softens shadows created by the key light, top light adds dimension from above, and backlight creates separation from the background. These elements enhance the visual composition but do not serve as the principal source of light that defines the performance's overall illumination.