For the layman – How 3D Rendering Works. Part 7: Lighting

[ about a 20 min. read ]
Part 1: 3D models
Part 2: Materials & Shaders
Part 3: Textures
Part 4: Projection mapping & UV mapping
Part 5: Camera
Part 6: Composition

In the previous articles I discussed Camera & Composition. In this article I want to discuss light and lighting techniques in 3D scenes. Now composition and lighting are of course very intertwined. As in the previous article I discussed some key aspects in lighting with regards to composition. But in this article I will address more what methods 3D artists have available to illuminate a scene.

1. What is 3D lighting?

3D lighting is the complete collection of tools and techniques available to a 3D artist to simulate the concept of real world light in a 3D scene.

3D lighting normally consists out of 2 parts: Direct lighting & Indirect lighting. This is because in the real world our surroundings are illuminated by a combination of direct and indirect lighting.
There is a giant star in the sky, know as the sun, which shoots out rays of light in all directions. But because we as a planet are so far from the sun, its light rays seem to arrive as parallel lines. This is what we call direct lighting. But area’s that are not directly lit by the sun are not completely dark. This is because the direct lighting from the sun bounces around off of objects and indirectly illuminates those areas. This lighting is what we call ambient lighting or indirect lighting.

So the modern rendering software packages are attuned to generating a high quality simulation of this combination of direct and indirect lighting.
But what are the precise tools and techniques that we have available to generate such a high quality light setup? Well there are the following tools and techniques, which I will be discussing one by one below:

  • Skydome
  • Global Illumination
  • HDRI
  • 3D Lights
  • Emissive lights
  • 2. Skydome lighting

    Skydome lighting replicates the sun and sky setup as we see it in the world around us. It does this by placing a dome around the scene replicating the sky, and by placing a point on the dome that represents the sun. This provides the combination of direct and indirect lighting. The Skydome in the software looks like this:

    And if you render that scene you get this:

    3. Global Illumination

    Global illumination is not really a stand alone technique, but it is more an algorithm that render software packages use to calculate and crank up indirect lighting. I wanted to mention this separately, because it is a very common term in 3D lighting. We actually already used global illumination in the SKydome example above. Below you can see what Global Illumination added to that render:

    4. HDRI lighting

    Now instead of a standard Skydome, we can also use the dome and assign a so called HDRI texture to the dome. HDRI stands for High Dynamic Range Image. It is basically a panoramic image of a real world location, that is able to store the lighting of the location where it was made. A render software can translate these images and use them as light sources.

    Below you can see an HDRI example of a country road during daytime. The image seems like it is distorted. But if you remember the UV map article (you can find it here), this shape is actually what you get if you unfold a sphere into a planar form. This HDRI map thus fits perfectly on a dome.

    An HDRI produces very high quality lighting:

    5. 3D lights

    Point light

    A point light is a 3D light source that is a single point in space from which an equal amount of light shines in all directions. The closer an object is to the point light, the brighter it is illuminated. A real world equivalent of a point light is something like a light bulb.

    Area light

    An area light is a planar light source that has a specific shape or size. Often it is rectangular. An equal amount of light shines from every point on the plane. A real world equivalent of an area light is something like a window.

    Spot light

    A spot light is a light source that emits light in the shape of a cone. The spot light illuminates brighter the closer you are to the source and it illuminates brighter near the center of the cone. The shape of the cone, and the falloff of the light intensity towards the edges of the cone, can all be controlled by the 3D artist. A real world equivalent of a spot light is a flashlight.

    IES light

    The Illuminating Engineering Society (IES) created a file format that describes a light’s illumination behavior from a specific light source. They did this by measuring real world illumination data of lamps. The file accounts for a light’s light bulb shape, reflection of the light fixture, light intensity, etc. What this basically means is that IES lights are lights that have a real world illumination pattern. It adds an extra layer of realistic lighting effect. Below you see 3 different IES lights next to each other. Each has a distinct illumination pattern.

    6. Emissive materials

    In my article on Materials & Shaders I addressed different types of materials. Now there are also materials that, if assigned to objects, they make the object emit light. These are Emissive materials. You can change color and light emission intensities of the material according to your preferences. Emissive lights are more for accentuating purposes, and do not emit a lot of light. An application for emissive materials would for example be small LED lights in a 3D model, or maybe a television screen.

    7. 3-point lighting setup

    Now you can make all kinds of combinations with the 3D lighting tools mentioned above. But there is 1 Basic lighting setup that I want to mention. That is 3-point lighting. Because this is a lighting technique that is very commonly used to lit a subject. And it is good to be aware of how such a lighting setup is made.

    3-point lighting consists out of 3 lights that illuminate the subject:

    The Key light: This is the main light. It Illuminates the object from the front and a bit to the side.

    The Fill light: This is the secondary light. It is less bright than the Key light. It is placed on the opposite side relative to the Key light. In this way this light “Fills”-up the hard shadow area’s created by the Key light, and overall softens the lighting on the subject.

    The Rim Light: This is placed on the back side of the subject. It can be placed on either side of the subject, depending on the preference in the final shot. The Rim light illuminates the back rim of the object to highlight contours and separate the subject from the background.

    And if we put them all together, we get a 3-point lighting setup like this:

    Now in my example I also placed a backplate in the image that was not completely black in the center. This also helped to separate the subject from the background.

    Now If you want to go a little crazy, you can also add some color to the different lights and create a more artistic style:

    Or reposition the lights, adjust their intensity and add some HDRI lighting, to get some more dramatic lighting like this:

    That is it for 3D lighting. As always, let me know if you have any questions or comments below.

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