A Little to the Left

You can earn this achievement by completing a level two different ways. Not every level can be completed multiple ways, so the earliest you can get this achievement is Chapter 1 - Level 7.

Arrange the books on the shelf from tallest to shortest. This will give you one star and finish the level. Restart, and now arrange the books from thickest to thinnest. This will give you your second star for the level and unlock the achievement.

On a level that has 2 stars, you need to complete the twice using 2 different solutions. The first opportunity you get to do this is in Chapter 1, Level 7 (with the coloured books).

This guide will help you through all puzzles and all achievements in the game - Seeing in a New Light solutions can be found at 3:30 (first 2 star level). This didn't pop for me on that one for some reason, it popped on the second 2 star level at 10:04

A Little to the Left Walkthrough & All Solutions/Achievements