dev-libs/light provides almost same functionality as acpilight, though no fade and with incompatible interface. Imho this is still more that original xbacklight provides, so light could replace it just like acpilight - also enough fast to be used at high rates, like 10fps or more (e.g. handcrafted script, adapring backlight to ambient light). xbacklight wrapper could be added, but I'm not sure (yet), what scripting language is good to not cause as serious performance drop as with acpilight. Reproducible: Always
