Illumination model used in the "Raytracer in a weekend" series
It’s a “naive” Monte Carlo sampler so it’s too dumb to send rays toward lights— it shotguns.   But the light is just a hemisphere (like a cloudy day) so you don’t get punished with too much noise.   Cloudy days look pretty good in real life.   But if you try to add a small light it will work but get very very noisy.   The third book in that series uses one method to address this (basically sending more rate where lights are rather than shadow rays per se)