You got all that math to translate RGB to HSL. Should be understandable with the links that HenryPK gave.
The Hue that the effect takes as value is in the range 0-100.
The calculated (and standard) H is in the range is in the range 0-360
Normalised this means ...
Value to bring into the effect for Hue = (H / 360) * 100
The Saturation that the effect takes as value in in the range 0-100
That is also the range for the calculate S, so no prob here.
Value to bring into the effect for Saturation = S
The Luminosity that the effect takes is in the range 0-200.
Calculated L is the range 0-100.
But the plugin wants to 'adjust'. So, if there is already a value 50 present, it needs to be able to adjust (relative) that to zero.
This means that the plugins value effectively has a range 0-100, but (absolute) is using an offset of 50.
Luminosity value to bring in the effect = L + 50
All that makes the values that you feed to the plugin absolute, although its working is relative. But only if you start with a sprite that is pure red. Pure red = zero degrees in the colour wheel, has 100% saturation, and a luminosity of 50.