The theories of sensory ecology remind us how much we have forgotten to reconnect our senses to our ecosystems. Heliot is a heliosensor, a low-tech measurement tool to understand our luminous environment. Showing solar variations is a way of having a more sensitive relation to our daily lives. The device works with photochromic smart inks. Imperceptible solar fluxes are translated by colour variations in order to measure the qualities of the ambient light, without resorting to digital technology.