Using environment and sunlight

Iray considers the environment for illumination contribution. Good HDR environments are likely to contribute lighting information that results in very realistic final results.

When using environment lighting, it is important to consider the recommendations hereafter:

• When using sunlight, you can use the MDL function base::sun_and_sky as environment function. The correct settings to work with luminance values that are mostly consistent with those of real world sun and sky light on a clear day are:

      rgb_unit_conversion: color(1.0, 1.0, 1.0)
      sun_disk_intensity: 1.0
      multiplier: 0.10132
      physically_scaled_sun: true  // which is the default
  

• Avoid HDR images where the sun is not as bright as in real life. Otherwise the resulting image looks washed out. To determine whether the sun is bright enough, open the HDR with an image tool and take a look at the value of the sun. A sun of realistic size should be a few thousand times brighter than other parts of the image. If its intensity value is anywhere below ~1000 then the sun is too dark, and the resulting light simulation will look dull and lack the necessary contrast in the rendered image.
• Avoid low resolution HDRs, as the aliasing of small bright spots in the environment map will appear in the final picture and yield artifacts, especially in the shading/lighting of objects. Apply the optional blur settings to low resolution HDR images.

Figure 1. HDR with dull sun compared with compared with HDR with bright sun