An IBL (Image Based Lighting) instance in your scene gives you the use of HDRI type environments for scene lighting. This can also be used as a background for your scene, or purely for lighting purposes.
An alternative is to use the built-in high dynamic range sun and sky system: Physical Sky.
To achieve realistic lighting results from a Spherical environment, it is important to ensure that the chosen HDRI or IBL has a realistic dynamic range. For example, HDRIs of exteriors often do not show the sun as being sufficiently bright compared to the rest of the image. The sun (unobscured by cloud) should be of the order of 100,000 times brighter than the surrounding sky. If the sun is significantly fainter than this, the final image may be unrealistic. Typical results are an overly blue tint to the scene (due to the relatively stronger contribution from the sky), soft shadows, and a general lack of contrast.
Adding a light
Create Panel ➤ Lights ➤ Dropdown ➤ IBL button
Parameters
Image:
Map Button: Use the map button (says ‘none’ when empty, and the filename of the HDRI when in use)
Intensity: Increases or decreases the contribution of the HDRI to the lighting
Mirror Image: Flips the attached map horizontally
Preview in viewport: Shows the HDRI in the viewport
Wireframe Preview: Shows the environment in wireframe form in your viewport
Shape:
Dropdown menu gives the option for Hemisphere or Spherical environments
Radius: Increase or decrease the size of the environment
Cam Height: Moves the HDRI up or down within the environment
Ground
Shadow/Reflections
Shadows: Toggle for shadow visibility on the ground plane of your environment
Density: Controls the strength (darkness) of the shadow
Reflections: Toggle for reflections on the ground plane of your environment.
Glossiness: Range is from 0 to 10,000,000 - 0 gives diffuse reflections and 10,000,000 gives perfect mirror reflections, with numbers in between giving varying degrees of glossiness
✱ Note:Iray+ Interactive renderer does not display varying degrees of glossiness — in general, glossiness will not be displayed except for values greater than 20,000, when perfect mirror is used.
Reflectivity: Adds a color tint to the reflection
Ground Height: Defines where the ground plane is on your model. Change this if the base of your model is not sitting on the ground plane correctly.
✱ Note: Iray allows one Physical Sky or IBL environment to contribute to lighting at one time, however you can add and keep as many inside the scene as your require. To choose the active environment, when there is more than one in the scene, use the Active Environment setting in Settings.
Create Panel ➤ 
Lights ➤ 
Dropdown ➤ IBL button
