What physical property allows objects to be visible in the dark?

Luminance is the property that allows objects to be visible in the dark because it refers to the amount of light that is emitted, reflected, or transmitted by an object. When an object has luminance, it can either generate its own light or reflect light from other sources, making it possible for us to see it even in low-light or dark conditions. For instance, objects that emit light, such as stars or glow-in-the-dark materials, possess high luminance, allowing them to be seen without any external light source.

In contrast, thermal energy, reflectivity, and density do not directly contribute to an object's visibility in the dark. Thermal energy relates to temperature, reflectivity pertains to the ability to bounce light off its surface, and density refers to mass per unit volume, which does not inherently affect visibility. It is luminance that is crucial for visibility under low-light scenarios.