How to Convert CIELAB to HSL
Converting CIELAB (Lab) to HSL moves a color from an absolute, perceptually uniform space into a relative, cylindrical space. While Lab is mathematically superior for color accuracy, HSL is often required for legacy systems or specific design tools.
Perceptual vs. Relative Lightness
The biggest difference between these two formats is how they handle lightness. In Lab, the L channel is absolute. A lightness of 50 is exactly halfway between black and white as perceived by the human eye.
In HSL, lightness is relative to the hue. A pure yellow and a pure blue can both have an HSL lightness of 50%, even though the yellow appears much brighter. When converting from Lab to HSL, you will often notice that the lightness percentage changes drastically to accommodate the flaws in the HSL color model.
The Conversion Process
There is no direct path between Lab and HSL. The conversion requires translating the Lab color into the CIE XYZ reference space, converting that to linear RGB, applying gamma correction to get standard sRGB, and finally calculating the Hue, Saturation, and Lightness from those RGB channels.