In the real world single particle of light hardly ever arrive at the same place at the same time. A group of photons could arrive at the same place at different times or at the same time at different places. The true nature of light is to preserve the status quo of minimum energy for each single photon such that each has a unique location in spacetime.

This state of perfect symmetry of minimum energy configuration is properly called quantum vacuum. On the other hand without fluctuations the vacuum would remain in a state of total perfection. The effect of random fluctuations is to force light’s tiny arrows pointing in the same spacetime direction when they arrive at the same spacetime location. The convergent effect is the ability to add up each zero-point energy of every single photon. This is done in the science of linear optics by lenses and in the science of nonlinear optics by laser principle.