Lightmap (Lightmap / Light baking) is a technical term that is extremely important in rendering and optimizing game graphics (technical art). Explanation of a technology that eliminates the light calculation load during runtime by calculating the gradation of light and shadow that hits the surface of a static object in advance using high-precision offline calculations and superimposing it on the model as a 2D texture.
Real-world analogy: Before the actors go on stage, the magic trick is to apply ``beautiful light and shadow gradation paint'' by hand perfectly on the white walls of the props
Lightmap is a method of precisely drawing in paint (texture) the light pattern itself on a prop (a static background object) in advance, such as ``Light shines into this place from a window, and a soft shadow falls behind this wall.'' When the game is running, the GPU does not need to calculate a single pixel of light. Simply pasting a "wallpaper texture with lights on it" onto the model and displaying it is a magical optimization where the load is completely "zero" even if there are hundreds of lights.
Diagram: An infographic that clearly illustrates the basic processing flow and mechanism of Lightmap (Lightmap / Light baking) in Japanese notation
Detailed mechanism and operating principle
Set the object and light Mode to "Static / Baked" and paste a high-precision Lightmap (Lightmap) in advance (image generation by pre-computation) and paste it, completely bypassing the real-time light calculation.