In the framework of quantum mechanics, light can exhibit both wave-like and particle-like behavior. This duality is often referred to as wave-particle duality. The specific instance at which light behaves as both a wave and a particle simultaneously is not well-defined.
The behavior of light depends on the experimental setup and the way it is observed or measured. In some experiments, light exhibits wave-like behavior, such as interference and diffraction, where it demonstrates characteristics of a propagating wave. In other experiments, light behaves as discrete particles called photons, such as in the photoelectric effect, where it interacts as individual particles.
The outcome of an experiment depends on the measurement being performed. If a measurement is designed to observe wave-like properties, such as interference patterns, the results will reflect wave-like behavior. Conversely, if a measurement is designed to detect particle-like properties, such as the detection of individual photons, the results will correspond to particle-like behavior.
It's important to note that the wave-particle duality is not unique to light but is a fundamental aspect of quantum mechanics that applies to all particles, including electrons and other subatomic particles. The behavior of particles is context-dependent, and their wave-like or particle-like nature is revealed through the interaction with the experimental setup and the act of measurement.