The best rulers are made from light! From gravitational wave interferometers to surface diagnostics, to the definition of the meter, optical interferometry is at the heart of precise measurement. Generally one improves interferometer precision by increasing the light brightness and trying to calm the many technical sources of noise that can perturb the mirrors or optical path. However, at extreme levels of light strength where radiation forces are significant, a new and interesting disturbance should appear – the quantum shaking associated with random arrival of individual photons at a mirror of the interferometer. This quantum backaction of light has been long foreseen in gravitational wave searches and played a formative role in quantum optics theory. In this talk I will discuss experiments in which we use a particularly compliant micro-scale, vibrating mechanical element to finally observe this effect in an interferometer. In this strong-light limit, interferometer mirrors can also be used as a nonlinear medium to manipulate light – for example to make squeezed light. We are also pursuing ways to translate more complex quantum states into light by coupling superconducting elements to an interferometer mirror.