id Software explains why DOOM: The Dark Ages moved to ray-traced global illumination
DOOM: The Dark Ages uses Ray-Traced Global Illumination, and id Software has now shown why that change was needed. During a SIGGRAPH 2025 presentation, which has just gone public, the studio compared the game against the older global illumination system used in the idTech 7 era. According to the slide, using the same older baked GI approach could have required up to 110GB of lighting data and up to 68 days of processing time.
Baking means the lighting is calculated before the game ships or before a level is finalized. The developer runs an offline process that checks how light hits walls, floors and objects, then stores that result as data. This can make runtime performance easier to manage, but every major map change can require another bake. For large games, this can turn lighting into a storage and production problem.
Source: id Software
Ray-Traced Global Illumination works differently. Instead of relying only on precomputed lighting, the engine traces rays in real time to estimate how light bounces through a scene. This helps with indirect lighting, darker corners, color bounce and moving objects. It also means lighting can react better when something changes in the scene.
Fun fact: DOOM: The Dark Ages uses Ray-Traced Global Illumination. If it had used older baked GI tech instead, the lighting data could have required up to 110GB and taken up to 68 days to bake 👀
From: https://t.co/Xo74fE97Mz pic.twitter.com/HnmTcRxvvX
— Jacob Freeman (@GeForce_JacobF) May 5, 2026
Global Illumination, or GI, is the general term for indirect lighting. It describes light that does not come straight from a lamp, sun or fire, but bounces off surfaces first. RTGI is one way to do GI. Baked GI is another way. The difference is that baked GI stores the result ahead of time, while RTGI calculates much more of it while the game is running.
Keep in mind that the slide is a rough developer-side estimate for older lighting data and production time. It does show why id Software moved to a more dynamic system for larger levels, more complex geometry and modern lighting requirements.
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