Unity 3D Developer Interview Question:

Explain why deferred lighting optimizes scenes with a lot of lights and elements?

Submitted by: Muhammad

During rendering, each pixel is calculated whether it should be illuminated and receive lightning influence, and this is repeated for each light. After approximately eight repeated calculations for different lights in the scene, the overhead becomes significant.

For large scenes, the number of pixels rendered is usually bigger than the number of pixels in the screen itself.

Deferred Lighting makes the scene render all pixels without illumination (which is fast), and with extra information (at a cost of low overhead), it calculates the illumination step only for the pixels of the screen buffer (which is less than all pixels processed for each element). This technique allow much more light instances in the project.
Submitted by: Muhammad