Gausian blur on masks?

When making a light out of a mask I wish I could blur only the effect more than by using a radial gradient and feathering. For example, I use a radial gradient to light an area like a street light. Even on max feather the light can be harsh. How about a gausian blur that only works on the gradient, not the underlying image. I don't want a gausian blur that changes the image, just the light and the effect it has on the underlying image. Hard to explain but feathering isn't enough sometimes.