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I used to convert to LAB for luminosity sharpening in Photoshop. However, this is already built-in in LR. It will concentrate the sharpening on the luminance channel therefore avoiding creating color artifacts. Remember that this is sharpening for the "screen". Before printing your photo, another sharpening step must be applied depending on the resolution and paper used. (Also excellent and built-in in LR)
When clicking on the option key on the Mac (Alt for PC) and moving the sharpening sliders, you will see a preview of the "Luminance" channel and how the sliders are affecting it. The detail and masking are very powerful tools.
You have to go beyond the default settings. Here are a few starting points:
1) Landscape photo well exposed shot with very low noise and lots of fine detail:
Amount: 45, Radius 0.7, detail 65 and Masking 0
2) Landscape photo with minimal noise (introduced in post production) and lots of fine detail:
Amount: 40 Radius 0.8 detail 30 and Masking 0
3) Portrait & High ISO photos:
Amount: 34, Radius 1.4, detail 20 and Masking 85
BTW: Lightroom has built-in sharpening presets for scenic and portraits that are already excellent.