How to Convert HSL to LCH
Converting HSL to LCH is a significant upgrade. Both color spaces use a cylindrical model (Lightness, a color intensity channel, and a Hue angle), but LCH is built on modern, perceptually accurate math that completely outclasses HSL.
Why LCH is the Better Cylinder
HSL was invented in the 1970s to give computer graphics pioneers a faster way to pick colors without having to guess RGB values. However, it is mathematically flawed. In HSL, lightness is relative to the hue, meaning a "50% lightness" yellow is vastly brighter to the human eye than a "50% lightness" blue.
LCH (Lightness, Chroma, Hue) fixes this by basing its math on human vision rather than monitor hardware. In LCH, the Lightness channel is absolute. This makes LCH the ultimate tool for generating accessible, high-contrast color palettes, because you can guarantee the perceived brightness of a color just by looking at its L value.
Chroma vs. Saturation
In HSL, Saturation is a strict percentage from 0% to 100%. In LCH, Chroma represents the actual amount of color present. Because human eyes are more sensitive to certain colors, the maximum Chroma varies depending on the hue. A vibrant yellow might reach a Chroma of 130, while a vibrant blue might only reach 100.
The Conversion Process
To convert HSL to LCH, the color must be translated into RGB, linearized, converted to the CIE XYZ reference space, and then transformed into CIELAB. Finally, trigonometry is used to convert the a and b axes of Lab into the Chroma and Hue of LCH.