According to quantum physics, light is composed of particles called photons, which are massless particles. Photons have energy and momentum but do not possess mass or weight as traditionally understood in classical physics.
The double-slit experiment is a famous experiment that demonstrates the wave-particle duality of light. When light passes through two slits and interacts with a screen, it creates an interference pattern characteristic of waves. However, when the intensity of light is reduced to a very low level, it behaves as individual particles or photons that create a pattern of discrete spots on the screen.
The fact that light exhibits wave-like properties in some experiments and particle-like properties in others can be challenging to comprehend. However, the conclusion is that light does not have mass or weight in the traditional sense, regardless of whether it behaves as a wave or a particle in different experimental setups.
As for the weight per square meter of surface area, since light has no mass, it does not have weight either. Weight is a measure of the force exerted on an object due to gravity, and since photons are massless, they are not subject to gravitational forces.