If you take a closer look at a real-world light source, whether it’s a light bulb, neon tube or candlelight, you will see that light is always emitted from a certain shape or surface. An Omni light, and in a lesser capacity a Spot light, can only emit light in an approximate shape. In the image below, the sphere at left is illuminated by an Omni light and the sphere at right by an Area light. Both the distance and intensity of each light are the same.
An Area light disperses its light across a large area. The brightness of the illuminated objects will be reduced slightly, becoming more even and lessening in contrast. Applied correctly, this light can be used to light objects more realistically and create more precise lighting setups.
The Area light’s Detail tab parameters
Contrary to the previously described lights, the Area light can assume various shapes. In the Details tab’s Area Shape menu, various default shapes can be selected, e.g., Disc, Rectangle, Line or even Hemisphere, among others. You can even assign a polygon object or Spline curve by selecting the Object / Spline option.
Size and aspect ration can be adjusted using the Outer Radius and Aspect Ratio values as well as the Size X, Size Y and Size Z values. The many available shapes make it possible to create innumerable types of light shapes. The Hemisphere shape can even be placed above an entire scene to illuminate it with a diffuse light.
How Area Lights Emit Light
The emission of light from an Area light can be compared to numerous Omni lights emitting from the surface. These virtual lights emit perpendicularly from the surface of the Area light. Light is also emitted peripherally. How strongly the emitted light should be dispersed is defined by the Falloff Angle value. The strength of the light will decrease as its angle to the surface increases. This is demonstrated in the image below. At top left is a simple scene setup with a Rectangle Area light between two spheres. To the right of the scene setup, the Falloff Angle value is decrease in increments of 30° from 180° to 90° in the bottom image. As you can see, the illumination of the spheres changes only slightly.
This additional fine-tuning option makes Area lights very versatile. For example, a rectangular Area light can be fitted into a window frame to simulate sunlight passing through a window. Using the Falloff Angle option you can define precisely which areas of the room should be reached by the light.
Area Lights’ Visible Properties
The Show in Render and Show in Reflection options can also be very useful. With them, an Area light can also be used in the form of illuminating geometry. The Area light can, for example, be used as a reflective foil or soft box for photography. The Area light’s shape can be made to either reflect on surfaces or appear as a colored surface in the camera view. This can be better explained using the image below. On the left is the test scene we used in our previous example with the Rectangle Area light between two spheres. By enabling the Show in Render option the light’s plane itself will be made visible. The brightness with which this plane is displayed can be defined separately from the light’s brightness using the Visibility Multiplier. In addition, or instead, the Show in Reflection option can also be enabled, which will also reflect the light source in the objects (this can be seen in the image on the right). To emphasize this effect, each sphere was assigned a chrome material.