Researchers from NVIDIA and the Visual Computing Lab at Dartmouth College created ReSTIR, a new algorithm capable of rendering dynamic direct lighting and shadows from millions of light sources in real-time. The algorithm is discussed in detail in this paper (PDF) and WCCF Tech offers a summary over here. The new approach is anywhere from 6 to 60x faster than previous techniques, like the Dynamic Many-Light Sampling for Real-Time Raytracing by Moreau et al., 2019.
In the impressive video demonstration embedded below, this raytracing algorithm managed to do all this while tracing 8 rays per pixel at most, rendering scenes containing up to 3.4 million dynamic and emissive triangles in under 50ms per frame. The GPU used was a GeForce RTX 2080Ti, with the exception of the Amusement Park scene, which according to the researchers had higher memory requirements and thus required using a Titan RTX graphics card instead.
Overall, this approach is 6-60x faster than the previous state of the art methods (such as Dynamic Many-Light Sampling for Real-Time Raytracing by Moreau et al., 2019) when using an unbiased estimator and 35-65x faster when using a biased estimator (which further reduces noise at the expense of some image darkening and energy loss). Another major takeaway, according to the researchers, is that denoising and filtering do not have to be restricted to post-processing once rendering is done, as with the ReSTIR raytracing algorithm denoising is part of the core renderer and filtering handles PDFs (probability density functions) instead of colors.