Importance Sampling

Robust Monte Carlo Methods for Light Transport Simulation

the Academy Award-winning Ph.D. thesis by Eric Veach. It starts from bidirectional light transport algorithms and introduces multiple importance sampling and Metropolis light transport

Ray Tracing/Path Tracing
PBR/Light Transport
Randomness/Monte Carlo
paper
classic

What is direct lighting (next event estimation) in a ray tracer?

An explanation of direct lighting and next event estimation in ray tracers

Ray Tracing/Next Event Estimation
article