Phew! Thanks everyone, I feel a little better
I suppose leaving a small floor lamp on isn't as bad as if I had left my actual grow lights on, but you hear stories of people claiming things like "oh I accidentally cracked the door to my flower room while it was dark, and all my plants turned hermie."
These must be old wives tales but I now must admit I'm not sure what it would take to cause a plant to hermie? I suppose some sort of light leak would do it, but surely there must be a threshold right? I mean even in the wild, plants are still exposed to moolight, starlight, and in modern society, passing headlights, porch lights, flashlights etc.
My own flower room for instance has a few minor lights leaks because there is a window in the room which I've sealed with a piece of opaque black dropcloth. But if I sit in the dark for a minute and allow my eyes to adjust, I can see a few pinpricks of light coming through the duct tape. No matter how much tape I use I can never seem to get em all.