Differences between local illumination and Global Illumination

Local illumination (local illumation) simply refers to the illumination effect from the light source to the model surface.
Global illumination) simply put, Ray Tracing and Radiosity are used to calculate the global illumination of all surfaces and light sources in the environment, the effects and shadows of light passing through the glass, as well as the shadow generated by simulating precise Direct Illumination, Radiosity, calculate the amount of light emitted by each element on each surface, and save it to the mesh.
Basic Terms of Optics
1. Luminous flux: the number of light shadows that arrive, exit, or pass through the surface per unit time. The Unit is lm (lumen)
2. Illuminance: the luminous flux of a surface area. The Unit is lx.
3. Luminance: it is a reflection of light and shadows on one side of a surface. Unit: cd/㎡. Kandra/square inch