The complexity of light interactions differs between real-time and offline rendering primarily in computational detail and realism, constrained by their speed and performance needs.
Real-time rendering prioritizes interactivity (e.g., games, VR), using simplified light calculations: baked lighting, approximated shadows, or screen-space effects to maintain high frame rates.
Offline rendering, unburdened by real-time speed limits, simulates complex light behaviors (e.g., ray tracing, global illumination, multiple bounces) for lifelike reflections, refractions, and indirect lighting, used in movies, animations, or high-quality product renders.
In summary, real-time uses simplifications for interactivity; offline uses detailed simulations for photorealism.