How is luminance defined?

Luminance is defined as the brightness of a surface as perceived by the human eye. It is a measure of the amount of light that is emitted, reflected, or transmitted from a surface in a particular direction. This concept is crucial in various fields, especially in imaging and display technology, as it relates to the effectiveness and quality of visual representation.

Understanding luminance involves recognizing that it is not just about the quantity of light present, but rather how bright a surface appears when illuminated. It is measured in units such as candelas per square meter (cd/m²) and is critical for ensuring that images are visible and interpreted correctly in applications such as radiology and fluoroscopy, where accurate visual information is paramount.

The other options focus on aspects of light that don't specifically define luminance. For instance, ambient light refers to general lighting within an environment, overall light level pertains more to illumination than surface brightness, and light absorption relates to how materials interact with light, which doesn't capture the concept of how bright a surface appears when viewed.