Why can light appear as a wave in some experiments and a particle in others?

The idea that light must be exclusively either a wave or a particle is a classical misconception. According to the Copenhagen interpretation of quantum mechanics, which was developed by Niels Bohr and Werner Heisenberg, light exhibits different characteristics depending on the experimental setup used to observe it.1

This concept is known as the complementarity principle. It posits that wave and particle aspects are complementary descriptions of an underlying reality that cannot be fully captured by either classical model alone.21

• Wave-like behavior: Experiments such as the double-slit experiment demonstrate interference patterns, which are characteristic of waves.2
• Particle-like behavior: Phenomena such as the photoelectric effect show light interacting as discrete packets of energy, or photons.23

Rather than light "switching" between these states, quantum mechanics reveals that these are simply different ways of observing the same phenomenon, both of which are necessary for a complete physical description.21