What At night a lamp appears brighter to someone sitting near it than to an observer across the room. Which term describes this difference?

The term that describes the difference in perceived brightness of a lamp to observers at varying distances is "luminance." Luminance refers to the amount of light emitted or reflected from a surface in a given direction, and it can vary based on the observer's distance and angle relative to the light source. The phenomenon can also be influenced by the inverse square law, where the intensity of light diminishes with distance from the source.