Ray Tracing is a rendering method that accurately simulates the behavior of real-world lighting by calculating and tracing the paths of light rays as they interact with objects in a scene. This results in lifelike shadows and reflections, drastically enhancing photorealism and fidelity of visualizations. 

1. Here's how to use it:

In Lumion, the Ray Tracing   engine is enabled via an Effect in Photo or Movie Mode.

The Effect can only be enabled if your PC has a Ray Tracing-capable graphics card. Please consult section 1.6 for compatibility:

• Knowledge Base:  Which graphics card do you need for Lumion 2024?

Also, Windows must meet at least minimum requirements, preferably fully updated.  See:

• Knowledge Base:  What kind of computer does Lumion 2024 need?

If your graphics card supports this technology, simply add the Effect to a Photo or Clip to enable the Ray Tracing engine. You can find it in the Featured or Lighting categories:

You'll instantly notice a great improvement in shading, reflections, and overall ambient lighting:

Other benefits of using Ray Tracing :

• Area Lights and Emissive Materials now cast shadows. 
• All light sources interact better with Subsurface Scattering.
• You get perfect Reflections without the need to manually add Reflection Planes.
• Glass casts shadows and can now be used with Depth of Field.
• No screen-space effect, which means Emissive surfaces that are not facing the camera still cast light.
• More natural colors.

Since Ray Tracing takes care of emulating how the light behaves with greater precision and realism, the following Effects will get disabled when the Ray Tracing Effect is applied to the Photo or Clip. 

• Global illumination Effect. (Lumion 2023 only, this Effect has been deprecated (no longer available) for Lumion 2024)
• Hyperlight Effect.
• Reflection Effect.
• Skylight Effect.
• Shadows Effect.

2. The Effect's settings:

In Lumion 2024, there are now 6 adjustable options in the Ray Tracing Effect :
 

2.1: Quality Presets

The Ray Tracing comes with 4 different preconfigured Quality   settings. The Samples , Bounces , and Fully Ray-traced Glass  toggle will change depending on what preset you choose:

Photo Mode:

Movie Mode:

The preconfigured settings are different in Movie Mode because videos use a different Denoiser that renders faster while requiring fewer Samples .

Changing any setting will set the Quality   preset to Custom .

2.2: Samples

This slider adjusts the number of rays shot per pixel per frame to control the accuracy of light: the bigger the Samples value, the higher the number of rays shot and intersections calculated, which results in greater rendering accuracy and level of detail:

Note that a higher Samples value will boost quality but will also result in longer rendering times, so increase it only when necessary, for example, on low-lit indoor scenes (which usually produce more noise).

However, for well-lit interior environments and exterior scenes, (or quick draft renders), a low number of Samples (around 16) usually does the job. Example below:

So, if you don't see much of a difference when increasing Samples , you might as well reduce the setting to save valuable rendering time. 

This is especially the case in Movie Mode , as it uses a different Denoiser that can produce usable videos even at 1 Sample .

2.3: Bounces

The number of Bounces   simulates the interaction of light with non-reflective objects. When a light ray hits an object, it is randomly deflected in a certain direction and the result is a converged image with smooth 'blending' between different surfaces in the rendering whose colors affect each other. 

The higher the value, the better the global Illumination:

You will usually need more Bounces   in indoor scenes, where you want to have as much realistic light bounce as possible.

2.4: Denoiser

Noise commonly occurs in Ray-traced   renders due to the complex calculations involved in simulating light behavior. The Denoiser is a crucial tool used to reduce the amount of graininess in Photos and Movies , and it works by analyzing the noisy image and intelligently smoothing out these imperfections while preserving important details, resulting in a cleaner and more visually pleasing final render. 

By effectively removing noise, Denoisers help enhance the overall quality of rendered images, making them appear more polished and professional. An unneeded high number of Samples may not require denoising if the lighting conditions are right, however, it will result in longer rendering times.

2.4.1: Movie Mode Denoiser Options
In Movie Mode , you'll notice there's an additional option to select between two Denoisers : 

• OIDN: This is the Denoiser used in Photo Mode . It employs sophisticated denoising algorithms that achieve high-quality results but may require more computational resources and time to process. When time is not a concern, consider trying OIDN as it might produce better-quality reflections.
• NRD: This Denoiser is optimized for efficiency and speed, leveraging techniques such as hardware acceleration and neural network inference to deliver fast denoising performance while keeping a good framerate, so it might not be as sharp as OIDN but is well suited for real-time rendering and rendering videos quickly. 

2.4.2:  How the Denoiser options work

1. When the Denoiser is ON in Photo Mode: Preview is denoised with NRD // final output is denoised with OIDN.
2. When the Denoiser is OFF in Photo Mode: Preview is denoised with NRD // final output is not denoised.
3. When the Denoiser is ON in Movie Mode (i.e. something is selected in the Denoiser dropdown): Preview is denoised with NRD // final output is denoised with the Denoiser that is selected.
4.  When the Denoiser is OFF in Movie Mode (i.e. nothing is selected in the Denoiser dropdown): Preview is denoised with NRD // final output is not denoised.

2.4.3: Summary of Denoiser Options:

• Preview:  NRD is used all the time.
• HQ Preview: OIDN is used all the time.
• Final Render - Denoiser On:
  • Photo Mode default Denoiser: OIDN.
  • Movie Mode: option you select (NRD or OIDN).

2.5: Firefly Filter

In Ray-traced   renders, fireflies are small, bright, unwanted artifacts that appear as isolated, high-intensity pixels scattered throughout the image. These fireflies often result from the complex interactions of light rays with surfaces and materials in the scene and typically appear in low-light scenes, on reflective surfaces, or when there are extremely bright lights. 

To tackle this, Lumion has a Firefly Filter   feature:

The Firefly Filter will take a pixel and look at all its neighboring pixels. If the difference between the neighbors and the current pixel is too large, then it will be replaced with the avarage color of its neighbours, resulting in a cleaner image, even in the Ray-traced Preview :

Notice how the fireflies in the ground Material, poles, and trees are reduced when turning on the filter. 

2.6: Fully Ray-traced Glass

Lumion 2024 introduces Fully Ray-traced Glass . Enabling this setting will cause Glass to have additional properties for the index of refraction and reflection, which results in a more authentic look and eliminates certain limitations that regular Glass has.

• Knowledge Base: The New Glass Material for Lumion 2024 and the Glass setting for Ray Tracing

5. Technical Limitations:

The Ray tracing Effect  will display an incredible increase in the quality of the rendered output. However, there are certain limitations in its usage described in the article below: 

• Knowledge Base: Transitions: From prior versions to working with the new Lumion 2024

See Also: 

• Knowledge Base:  What does the message 'Low VRAM detected' mean?
• Knowledge Base: Why is the Raytracing Effect blocked on my PC?
• Video Tutorial:  Lumion 2023: The Raytracing Effect