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Lab is not energy linear, and if you're doing rendering/illumination, you won't want to use Lab (unless you're deliberately trying to stylize). It is designed to be a good model of human color perception, not the physics of light.

Lab color space is good for mixing colors in a way that behaves intuitively. E.g. "what color is 'halfway between' these two other colors?", mixing "paint" digitally, producing pleasing gradients, picking colors or creating palettes.