light:change the overall brightness of the output. this is the reciprocal lambda parameter of the weibull distribution
contrast:contrast of the output. this is the k parameter of the weibull distribution
bias:offset to add to black pixels. use to lift for low contrast renders and to correct elevated raw black level
colour:how to reconstruct colour after applying the curve to the brightness channel. darktable ucs has in general better colours, but hsl is more robust for edge cases near black. munsell is data driven and navigates brightess by munsell coordinates.
