Real-time rendering simplifies light source calculations to prioritize speed, while offline renderers use complex, physically accurate simulations for higher quality.
Real-time rendering often employs approximate techniques like shadow maps or ambient occlusion to reduce computational load, enabling instant visual feedback in applications such as video games. Offline renderers, by contrast, use methods like path tracing or global illumination to accurately simulate light bounces and interactions, resulting in more realistic lighting but requiring longer rendering times, common in movie CGI or architectural visualization.
For quick previews or interactive experiences, real-time rendering is ideal; for high-fidelity, detailed lighting effects, offline rendering is better suited.