The Instagram effect added in February 2012 that lightens shadows and increases contrast is Lux.
Lux was introduced as a one-tap enhancement for photos that looked dull, underexposed, or low in contrast. Its processing was designed to reveal detail in darker areas while giving the image more tonal definition. Instagram also described it as darkening highlights, so the effect was not simply a brightness boost.
The feature arrived during Instagram’s early iPhone-focused period, when the app was known mainly for square photos and stylized filters. Lux was different from a conventional color filter: it adjusted the image’s lighting and contrast rather than applying a strong retro color treatment.
A common mix-up is confusing Lux with filters such as Ludwig, Crema, or Aden. Those names refer to later filter additions, while Lux was an enhancement tool introduced in February 2012. The name also suggests light: “lux” is a unit used to measure illuminance.