As I wrote in the previous post, my accountant notices that the ZonnenBoxen® on her office windowsill get moved when she is not there. This post contains the photo which shows the little wall-like structure she built and the one---yellow---block that got shifted by the unseen hands. Note how the boxen are glowing in this photo : that is indirect north light about 4 pm . No lights were on in the office. They do seem to use the light around them.