What is the dual nature of light?

Answer 1

Because we don't know what light is exactly we use models to try and help describe light, given what we've observed.

There are two main models. Particle model and Wave model.
Both have their strengths and weaknesses, but both are essential when trying to describe different properties of light.

Particle Model predicts that light behaves like a particle. This can be seen in the way light reflects off a mirror, it behaves like a ball bouncing off a wall. It behaves like a particle.

However light diffracts around corners, this can only be explained by the wave model. Also explained by wave model is constructive and destructive interference caused when two different light sources overlap. The troughs and crests of the 'wave' of light interfere, causing light and dark patches on a screen, this is called and interference pattern.

So basically, the dual nature of light is that it behaves like a particle and like a wave.

Answer 2

Particulate and wave nature. Diffraction is a typical wave nature which cannot be explained by particulate theory and the photoelectric effect could not be explained by the wave model. Quantum theory came to account for both.