When using IES light, you will need to load an IES profile by clicking on the folder icon in the editor. As soon as you load the profile you will see the shape of the IES profile in the material preview. You will also see the shape in form of a mesh in the realtime window.
File This displays the name and location of the IES profile being used. Click the folder icon to change to a different IES profile.
Color Here, you can choose the color the light will cast. Use the Kelvin scale to select accurate lighting temperatures.
Multiplier Adjust the intensity of the light with this slider.
Radius Here, you can adjust the radius to control the falloff from shadows cast from this light.