> For the complete documentation index, see [llms.txt](https://docs.betterbuilding.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.betterbuilding.io/user-guide/workflows/daylight/surfaces.md).

# Surfaces

{% hint style="info" %}
Surface inputs are typically determined by a building code, guideline or rating tool in the early stages of design. Once materials have been determined, specularity, roughness, and reflectivity can be sought from your supplier.
{% endhint %}

<figure><img src="/files/CvhOdQTPJR2sAMQwZkj6" alt=""><figcaption></figcaption></figure>

In [Radiance](/support-and-training/other-support/testing-and-verification/radiance-v-5.2.md), specularity, roughness, and reflectivity are essential parameters used in the process of simulating how light interacts with materials and surfaces in a virtual scene. These parameters play a crucial role in determining the direction and intensity of reflected and scattered light rays, ultimately influencing the final appearance of the rendered scene.&#x20;

## Customised Surface

The Customised Surface options enable you to select a specific wall, ceiling or floor element of a space and set Reflectivity, Specularity and Roughness.

## Reflectivity

Reflectivity, or reflectance, represents the proportion of incident light that a surface reflects. It is the combined effect of specularity and roughness.

* Radiance calculates the reflectivity of a surface by considering both the specularity value and the roughness parameter.
* High specularity and low roughness contribute to higher reflectivity, leading to more focused and intense reflections.
* Low specularity and high roughness result in lower reflectivity, leading to more scattered and diffuse reflections.

## Specularity

Specularity refers to the ability of a surface to reflect light in a mirror-like manner, resulting in well-defined specular highlights. In Radiance, specularity is typically represented as the "specular reflection coefficient" or "specular reflection value."

* When a light ray intersects a surface, Radiance uses the surface's specularity value to calculate the direction of the specularly reflected ray. The calculation is based on the surface normal and the incident light direction.
* The specularity coefficient determines the intensity of the specularly reflected ray. Higher specularity values result in stronger and more focused specular highlights, while lower values produce weaker or more spread-out reflections.
* Specular reflections are particularly noticeable on materials like polished metals, mirrors, and glossy surfaces.

## Roughness

Roughness is a measure of how irregular or rough a surface is. Surfaces with high roughness scatter incoming light in multiple directions, leading to diffuse reflections and soft shadows. The roughness parameter is commonly used to represent this characteristic in Radiance.

* When a light ray intersects a surface with roughness, Radiance simulates the scattering behaviour of the light ray based on the surface normal and the incident light direction.
* The roughness parameter influences the probability of the light ray being scattered in different directions. Higher roughness values result in more scattering and less directional reflection, creating a softer appearance.
* Surfaces like rough concrete, fabric, and textured materials exhibit significant diffuse reflection due to their high roughness values.

## Shading Reflectivity

Shading Reflectivity includes attached, aspect, and site shading, presenting the proportion of incident light that these surfaces reflect. It is the combined effect of specularity and roughness.

* Radiance calculates the reflectivity of a surface by considering both the specularity value and the roughness parameter.
* High specularity and low roughness contribute to higher reflectivity, leading to more focused and intense reflections.
* Low specularity and high roughness result in lower reflectivity, leading to more scattered and diffuse reflections.


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