Amount to darken the unilluminated area by. Value of 0.0 results in no
darkening; value of 1.0 makes unilluminated area black.
Remarks
This method creates a reduced size preview for the Spotlights method effect. It accepts the same parameters you would use for the full size image, so you don't have to recalculate them to account for the reduced size of the preview.
The spotlights effect darkens the image and highlights selected areas as if they are illuminated with a spotlight or sunlight.