Unreal Engine 5 is finally out and ready for production. This release will be a significant step forward for the gaming industry. UE5 came with a lot of changes and upgrades on board. It also introduced a few completely new features like lumen and nanite. Lumen is a software-accelerated form of ray tracing, and it does the heavy work of tracing the paths of individual light rays at a much lower resolution, and then upscales the output to the native output. This reduces the system load by a huge margin. But, how good is this software accelerated form of ray tracing, and how does it stack up to the classic hardware-accelerated results?
Lumen vs Ray Tracing – Comparison
Both lumen and ray tracing mean almost the same. It is like comparing Call of Duty to first-person shooters. Thus, instead of comparing lumen and ray tracing, we will look at lumen versus hardware-accelerated ray tracing. To start things, let us understand how they work, briefly.
As discussed above, Lumen takes any given screen and renders a very low-resolution model of it. Light’s behaviour in this low-res mode is then recorded, and a rough lightmap is created. This lightmap is then used to trace the path taken by every ray in the scene. Then, the output lighting is upscaled and displayed as a cube map. All the heavy lifting is done by the engine, and Lumen does not affect the assets put together in a scene. Thus, it is an innovative solution to the extremely intensive hardware-accelerated ray-tracing method.
Hardware-accelerated ray-tracing relies on specific high-performance cores called RT cores found within graphics cards. These cores are dedicated to the job of calculating the path taken by each ray in a scene and lighting up the scene accordingly. Thus, the more RT cores a graphics card has, the better it performs in ray tracing scenarios. Also, this method involves no upscaling, and all of the renderings are done in real-time. This makes them light up pretty much as they would do in real life.
Thus, you can tell that hardware-accelerated ray tracing is much better than Lumen. Lumen also has some other down points. Since the technology uses upscaling, it causes shimmering issues on higher resolutions like 1440p and above. Also, since the lighting technique involves converting the scene geometry to low-resolution models for recording the lighting, most of the details in the models are lost. Although big and flat models like walls are not affected by this, intricate assets like chandeliers lose significant detail. This results in unlit bugs in scenes. Also, walls less than 10 Unreal units thick are unaffected by Lumen.
The technology is nowhere near perfection, but the results are quite convincing.
Thus, in a tussle between Lumen and hardware-accelerated ray-tracing, the latter will always win. This comparison is much like the one between rasterization and ray tracing. Hardware-accelerated ray-tracing is a very intensive workload, and it requires some cutting-edge technology for perfect execution. Thus, the industry is always on the look for software-accelerated lesser intensive alternatives. Lumen is another such alternative, and even in its finest form with all forms of optimizations, it will still trick the human brain to think that the scene is ray traced, while it will never be. Thus, it can never match the level and quality promised by hardware-accelerated ray-tracing.