We have all heard of lectures that leave you in the dark, but never quite as completely as at Trinity College, Dublin. Not that the lecturers were at fault - despite its Anglicised image, Trinity usually manages standards of delivery that are all that you would expect of an Irish institition. The villain of the piece is an ingenious device introduced to stop lights being left on all night in some lecture rooms.
If sensors detect no movement for 20 minutes, lights are switched off automatically. All very simple if sensors were trained on the front of the room, where even the least-animated lecturer might be expected to twitch occasionally. Instead they are focused on the audience and the aisles. Fine, if the hall is full, or if anybody chooses to leave. Not quite so good if you have a small, passive audience concentrated in the wrong section. This leaves lecturers with a straightforward, if uninviting, choice - either running up the aisle three or four times per session, or being periodically plunged into darkness.