- Reflect light: Most of the objects we see around us are non-luminous and they appear visible because they reflect light from a light source, such as the sun, artificial lights, or even moonlight. The colour of an object depends on the wavelengths of light it reflects, while the brightness depends on how much light it reflects.
- Emit infrared radiation: All objects, even those that appear dark and non-luminous, emit some form of energy, including infrared radiation. While our eyes cannot directly detect infrared radiation, certain devices and cameras can, allowing us to "see" these objects in the form of thermal images or night vision.
- Create bioluminescence: Some organisms, like fireflies and deep-sea creatures, have the ability to produce and emit light through chemical reactions known as bioluminescence. This allows them to be visible in dark environments.
- Scatter or diffract light: Non-luminous objects can also be seen when light interacts with them through processes like scattering or diffraction. For example, fog or clouds appear white because they scatter sunlight in all directions, while rainbows are formed when sunlight diffracts through water droplets in the atmosphere.
