Chapter 14. Architectural Lighting

Developing clean, accurate, realistic lighting is essential for creating visualizations. The interplay of lights, shadows, reflections, and materials brings worlds to life, creating depth and telling stories. In this chapter, you learn how to set up great-looking Global Illumination (GI) lighting using Lightmass.

Unreal’s high dynamic range rendering pipeline combines with effects like auto-exposure and bloom to create a realistic, warm, and dynamic lighting environment. Getting your lighting right using these techniques can be tricky, but using some baseline settings you should be able to get great results quickly.

In this chapter you learn how to adjust Level and Static Mesh properties and settings to achieve great lighting with reasonable lighting build times.

The chapter also shows how to use post-processing effects like vignette, color grading, and depth of field to create a more photorealistic image (see Figure 14.1).

Finally, you learn how to place Reflection Capture Actors into the Level to improve lighting and help mirrors look more accurate.

Because of this, you cannot separate the two completely. This chapter and the next are intended to cover both topics individually; however, to get the best results you’ll use the techniques from both chapters in parallel.

Lightmass calculates the light hitting the surface of each Static Mesh in your scene using a photon-based, Global Illumination solver like Mental Ray. It then records this data to several Textures, called Lightmaps and Shadowmaps. This process is referred to as building your Static Lighting. Upon completing the lighting render, the Textures are automatically imported and applied.

As the name suggests, you cannot move or modify objects lit with Static Lighting or the lights used after you build them. If you add, remove, move, or otherwise modify the Static Lights or Static Meshes in your scene, you will break the lighting and must rebuild it.

Note that you can add lights to an already-built lighting scene. Although you will need to build your lighting again to see the GI contribution of these newly placed lights, the existing static lighting will remain. This can be helpful as you add more and more lights to your scene.

Lightmaps and Shadowmaps are stored in a special BuildData UMAP Level file (the custom file format UE4 stores Levels as) alongside your saved Level. This file and your project will grow significantly as you add more Assets because each one increases the memory overhead of the Lighting Textures.

The three main light types or classes in UE4 are Point, Spot, and Directional. Point and Spot lights radiate from a single point in space. They are great to use for nearby lights like lamps, fixtures, and spot lights. They are not great for the sun, which from our perspective here on Earth radiates light in parallel. For this, you need a light that simulates the light coming from a single direction instead. Enter the Directional Light Actor class.

Like most Actors, you can easily place lights into your scene by dragging and dropping them from the Class Browser into the Viewport.

You can place the light anywhere in your scene because it does not radiate from that point; only the rotation is important. I put mine where I can easily find it again.

Find a pleasing or realistic rotation for your light. The dynamic shadows act as a preview and give you a good idea where the static shadows will land (see Figure 14.2). Take a look around as you do this. UE4’s dynamic shadows provide a good approximation where the baked shadows will land in your scene.

The Details Panel shows the various options available for the selected light (see Figure 14.3). You need to adjust several settings to get the best quality and performance from this Light Actor.

Note that changing the Intensity does not affect the GI lighting because that is baked into Static Textures.

UE4 features an atmospheric light scattering fog system that simulates earth’s atmosphere. This is driven using an Atmospheric Fog Actor and the Directional Light Actor. Just drop an Environmental Fog Actor into your scene. If your Directional Light Actor has Atmosphere Fog Light enabled, it will orient a sun disk and set the sky colors based on the sun’s position, creating a simple but effective skybox.

In this example, let’s just capture the scene.

Place this light somewhere in your scene where you can find it easily. You will also want to ensure it is not enclosed within any geometry so it can capture the unoccluded sky. The Sky Light Actor has some settings to tweak to get optimal results (see Figure 14.4).

Setting Mobility to Static bakes all the indirect sky lighting into the Lightmaps and Shadowmaps generated by Lightmass, avoiding some of the inaccuracies that the stationary pipeline can introduce, such as light leaking or inaccurate lighting.

To build lighting, click the Build button in the Editor’s toolbar. You can click on the arrow next to it to see the settings. The most important is the Lighting Build Quality setting. This lets you quickly go from a fast preview build to a great looking but slow-to-render production quality build (see Figure 14.5).

Lightmass offers several presets for lighting quality from preview up to production. Production lighting builds can take orders of magnitude more time than preview builds, but lower quality builds can introduce artifacts and inconsistencies that can be hard to distinguish from actual issues with geometry or lighting.

Figure 14.6 shows a comparison between preview and production lighting builds. You can see that accuracy is greatly reduced with the preview build, but the lighting time was significantly reduced.

As you can see, even using production quality, the lighting still isn’t very good. Shadows are undefined, blocky, and low-res, and errors exist on the baseboards and in dark areas. By making a few adjustments, you can have this scene looking a lot better in short order.

The settings for Lightmass are stored on a per-Level basis and can be modified in the World properties options. The Lightmass panel offers a lot of settings (see Figure 14.7). Thankfully, UE4’s defaults are very good for most circumstances. Each setting has a dramatic effect on build times, so always starting small and working your way up is a good idea.

You should not adjust any other settings until you have disabled this setting. The noise it introduces will make your lighting unsuitable for architecture visualizations and no amount of tweaking can eliminate it.

Using uncompressed Lightmaps comes at the cost of memory. Uncompressed Lightmaps take up significantly more disk space than compressed Lightmaps. They also use more video memory when running in-game.

If your Level is very large (a stadium or an entire building) or you are targeting lower-end hardware (laptops, mobile devices, and so on), you might want to use the Compressed Lightmaps setting to allow these Levels to load into RAM.

Finding the balance can be challenging, but here’s one way to set Lightmap resolution in UE4:

1. Enable the Lightmap Density visualization by choosing View Mode > Optimization Viewmodes > Lightmap Density (see Figure 14.9).

When you first enter this mode, you will see something like Figure 14.10—lots of grids of varying sizes and colors with no lighting information. What you’re looking at is a visualization of the Lightmap pixels on each object in the scene. This helps you adjust the resolution quickly and interactively.

Blue indicates that the Lightmap resolution is too low and red indicates that it’s set too high. You should aim for green to orange on all your surfaces for the best quality with reasonable build times.

2. To adjust individual Mesh Actors in the Level, select each Mesh in the scene one by one and adjust the Overridden Light Map Res setting in the Details Panel.

After they’re adjusted, the Lightmaps should be much more even in density and higher resolution, as shown in Figure 14.11.

You do not need to set the resolution to a power of two (64, 128, and so on), but you should not go too big. Resolutions more than 1024 are supported but should be used sparingly. The higher the resolution, the longer the build time, the larger the Level on disk, and the more memory it takes up. Keeping it as low as you can without unacceptable artifacts is best.

Adjusting the Lightmap resolution on Props is different, so you adjust them at the Asset Level. This ensures that each one in your Level will have the proper resolution because the changes you make to the source Asset will be reflected by any scene Objects that reference those Assets.

Be aware that any changes to the Static Lighting settings for the Mesh Asset will break lighting in any Level that has the Asset referenced.

You can also adjust the density of Props on a per-Object basis in your Level using the Overridden Light Map Res property in the Details Panel. I sometimes give my Props (especially if they have a lot of detail or organic shapes) a higher relative density than Architecture Meshes, as shown in Figure 14.12, which makes them appear to be rather reddish in color.

Be careful; repeated Props can quickly generate a lot of high-resolution Texture data.

This is also a good time to save your work.

Getting the lighting brightness right is an art. It is affected by the number of lights in an area, the brightness of the sunlight, and even the color of the materials it’s reflecting off of. Brightness has a dramatic effect on the final look of your lights.

You need to iterate and adjust your lights to find a suitable balance for your scene and tastes.

Locking the exposure using the View Mode menu in the Viewport ensures the lighting brightness does not adjust as you move from light to dark areas, and more easily allows you to balance your lighting.

Place these Actors on your windows and other openings and loosely adjust the box to fit. You don’t need to be terribly exacting; it’s just a helper for the photons and doesn’t need to be precise.

Although you can get away without placing these around your Level, you do achieve much higher quality with them.

The two types of Reflection probes are Sphere and Cube. Simply put, for square-shaped areas, use the Box Reflection Capture Actor. For all other areas, use the Sphere. As you can see from Figure 14.14, a mixture of both kinds is useful to fine-tune the reflections in the scene.

Box Reflection Capture Actors expose a 3D Scale value. You should adjust the Scale of the box until the corners of the box shown in the Viewport fits as closely to the corners of your room as possible.

It’s also worth noting that Box Reflection Capture Actors have a higher performance impact than the Sphere Reflection Capture Actors.

When you create a new Level in UE4, default post processing settings are applied to the scene automatically. These settings are a good start, but you’ll almost always want to adjust them in each of your scenes to match its unique lighting and to achieve the look and feel you are after.

To access these settings, you need to add a special class of Actor to your scene: the Post-Process Volume.

You can adjust Volumes by setting their Brush settings. You can define the shape of the volume, as well as the size. You can also scale, rotate, and move them like any other Actor.

To access the settings, simply select the Post-Process Volume in the Level and look in the Details Panel.

The following are the settings you will be adjusting most often, and the ones adjusted for this example.

It’s important to note that only properties that have been manually overridden (by selecting the checkbox to the left of the property in the Details Panel for the overlapping volume) will be applied. This is a great way to adjust only a single property without having to ensure all the other settings match.

The default settings are often too contrasted, making shadowed areas very dark. This is a very filmic look, but it can be too dark for arch-viz where it might be preferable to have very dark areas.

These settings are very sensitive, so small adjustments go a long way.

Vignette adds a dark gradient to the edges of your image, which can allow you to increase the overall brightness of the image—the only fully bright pixels are in the very center of the screen.

Fringe simulates the chromatic aberration effect of light passing through a camera’s lens, separating the colors closer to the edges of the image.

Grain adds animated noise to the image. Grain Intensity controls the Noise Texture overlay’s opacity while Grain Jitter controls how much the grain displaces the image. Use these sparingly as they can become overbearing quickly.

UE4 reads the difference between the baseline image and the modified LUT and applies that delta to the scene. This is a great way to bring your existing color correction pipeline into UE4. You can find more information about LUTs and some LUT files for download on the companion website for this book at www.TomShannon3D.com/UnrealForViz

The default Bloom and Lens Flare settings in UE4 are a little aggressive and can decrease the contrast and clarity of scenes if used too much. Decreasing the Intensity or increasing the Threshold are good ways of reducing the overall amount of Bloom and Lens Flare in the scene.

You can also adjust the size of the effects. Larger sizes will have a more significant impact on performance.

I will often disable Lens Flares in scenes completely or turn them down so far as to only occur with extremely bright pixels.

This system can help create dynamic, engaging lighting interactions as your player moves from one area to another and sees the exposure adjust in response, much like the human eye or a camera with auto-exposure. It can also make setting up your lighting quite challenging.

I recommend setting up your lighting with Auto-Exposure disabled, then enabling it as-needed for your scene. You can disable this effect either through the Exposure Settings in the View Mode dropdown in the Viewport, or by setting the Min and Max Brightness parameters in the Post-Process Volume to 1.0. You can then use the Exposure Bias to manually set the exposure of the camera.

After your lighting is set up, begin to play with Min and Max Brightness to allow the camera’s exposure to adjust. To allow the camera to overexpose, brightening dark areas, set the Min Brightness to a value below 1.0. To allow the camera’s exposure to be reduced when in bright areas, increase the Max Brightness above 1.0.

To increase the blurring effect, reduce the Aperture F-Stop parameter’s value. Lower settings will produce more blurring (see Figure 14.16). It’s important to note that this is a realistic effect, so you might not notice the effect until you get very close to an object.

For an interior scene, you will want to ensure your Focal Distance is set to around 300–500 (3 to 5 meters) and the Aperture F-Stop is fairly large at 4–8.

The following example scene shows the result of enabling the Ambient Occlusion, Vignette, Grain, and Depth of Field settings. Each improves the look of the image, adding the imperfections and other effects one expects to see from a photograph.

As you can see, the settings in the post-process volume have a dramatic effect on the look of the scene. Even the subtle settings used here significantly changes the look and feel of the scene (see Figures 14.17 and 14.18).

This interaction between light, color, and Materials is familiar to visualization artists and is where technology diverges into artistry. Through practice you will learn to understand your instrument and begin to craft warm lighting effortlessly in UE4.