Boost Light brightens the image, increasing the illumination emanating from the Source Point.
In the three images above, we have Boost light with values of 0 (left), 7 (center), and 12 (right). As you can see, Boost Light offers an easy way to animate into or out of a completely white image, making it great for transitions. However, you may encounter situations (such as the images above) when increasing Boost Light no longer extends the illumination and fails to fill the layer. Using Boost Light with increasing Ray Length should fix this.