Here's a breakdown:

* Luminance: This refers to the brightness of a surface as perceived by the human eye. It's measured in units like candelas per square meter (cd/m²). Luminance takes into account how much light is reflected from a surface and how our eyes perceive it.

* Reflectance: This refers to the percentage of light that a surface reflects. For example, a white surface has high reflectance, while a black surface has low reflectance.

* Brightness: This is a subjective term referring to how bright something appears. While it's related to luminance, it can also be influenced by factors like contrast and adaptation.

In summary: While reflectance describes how much light is reflected, luminance is a more comprehensive measure that incorporates both the amount of light reflected and our perception of it.