At this time Blender contains decomposition nodes only for HSV and RGB, but not for HSL color model. Because I find HSL color model very useful for color manipulations, especially the Lightness value, I created both Separate HSL and Combine HSL nodes, which enables to modify each part of this color model.
The both nodes are created using existing Blender nodes, not by OSL script. So, you can use my nodes for GPU rendering. I didn't use OSL, because it doesn't work with GPU rendering.
Yes, It would be nice if such nodes were part of Blender. But I needed them quickly and had no idea how to add them to official release. I guess they need to be compiled to bytecode as all other default nodes.
Hello Meshlogic, thanks for sharing it with us.