I can't understand LC and CL tools

It’s long time I want to post something about this. There are two controls in the “Lab adjustments” panel that I can’t understand. All others (LH, CH and obviously HH and CC) work as I expect, but LC and CL don’t make sense to me.
For example, how I have to change the curve if I want to desaturate low values for luminance?
A tool that make sense to me for CL, would be an horizontal zero level of variation that works on different zones of luminance. Same behaviour of the CH where I can vary the saturation for different values of hue.

A picture that could show better than my poor english.

The simplest way is that you move the left endpoint toward the right.

Perhaps the next simplest way: make a point on the diagonal so that saturation is not changed for that luminance value and brighter, then move the left endpoint toward the right.

If these methods work for you, then you will see how to do the job with more sophistication.

I have figured out how to use the LC and CL tools as RTCharles has described, but I second support for the change bluc suggests, as CL and LC would be a lot more manipulable and intuitive as an equalizer. Davinci Resolve has similar curves that are in equalizer form, and I find that to be much more user friendly than an in/out curve. Resolve example shown below.

First of all, let’s agree that some parts of the user interface should be corrected (e.g., the left bar, because its lower part shouldn’t be white, but gray as in a real desaturation), the documentation should be clearly improved, and there should even be a better tooltip for each curve.

But a completely different thing is that any other interface is more intuitive, obvious or user friendly, just because different people think differently, and what is intuitive for you, may not be so much for me. Let me explain:

In your Davinci example, me as a user tend to think that I will get a huge transformation in the leftmost part of the shadows, and it will be increasingly moderate up to about 25% of the graph. Good!

It means that I will have an impressive desaturation of black (red arrow), and a bit less impressive in the green arrow grey. How much? I’m not sure…

On the other hand:


Here the red arrow vanishes, just because black can’t be desaturated (as explained in the other thread), and the green arrow tells me how much from the current colour values of that luminances the hues could be desaturated. If I drag the curve (the line) down to around the middle of that free space, those colors will become about half desaturated.

To me (again, to me) that’s more intuitive, but probably it all depends on what you are used to, or which software you come from, but not how wrongly is this interface designed.