IES light profiles are standardized files that can be used to modify light sources in 3D applications to mimic real-world lights and their attenuation and falloff. The Illuminating Engineering Society (IES) are the authority on lighting design guides that sets the standards. All 3D applications and third party renderers will allow you to use IES light profiles to light a scene, giving you more realistic lighting results and much more interesting light shapes as it falls on objects in the scene.
Working with IES light profiles with redshift is as simple as anywhere else. There is a special light type, the Redshift IES Light, that will allow you to assign a profile to it. What’s cool about Redshift’s implementation is that it changes the light object in the viewport to reflect the shape of the light object in the scene. This makes it really easy recognize different lights within the scene.
Small Robot Studio walks through some IES Light examples, and offers a nice resource where you can download light profiles for your work.