HSLuv is a human-friendly alternative to HSL.

Here you can see CIELUV, a color space designed for perceptual uniformity based on human experiments. When accessed by polar coordinates, it becomes functionally similar to HSL with a single problem: its chroma component doesn't fit into a specific range.

HSLuv extends CIELUV with a new saturation component that allows you to span all the available chroma as a neat percentage.