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
Parameters
Image:
Map: use the selected HDRI file (says ‘none’ when empty.)
Intensity: increases or decrease the contribution of the HDRI to the lighting.
Mirror Image: flip the attached map horizontally.
Preview in Viewport: show the selected HDRI in the viewport.
Wireframe Preview: show the environment in wireframe form in the viewport.
Shape:
dropdown menu gives option for Hemisphere or Spherical environments:
Radius: increase or decrease the size of the environment.
Cam Height: move the HDRI up or down within the environment.
Ground
Shadow/Reflections
Shadows: toggle for shadow visibility on the ground plane of your environment.
Density: control the strength (darkness) of the shadow. The higher the value, the darker the shadow.
Reflections: toggle for reflections on the ground plane of your environment.
Glossiness: control the strength of reflections in the ground plane. The range is from 0 to 10,000,000: a value of 0 gives diffuse reflections; a value 10,000,000 gives perfect mirror reflections; values in between give varying degrees of glossiness.
✱ Note: the 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 a perfect mirror is used.
Tint: add a color tint to the reflection.
Ground Height: define where the ground plane is in your scene. 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 you 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
