The building’s windows are slightly recessed, and when the sun hits the building at the end of the day at just the right angle, it lights up only the very edges of the window frames. The effect is to make it look like the building has been outfitted with a grid of light.
When it happens, it only lasts for about 5 minutes. I’ve been trying to capture it on camera for the last 10 years – but it usually happens just as I’m leaving for the day, and I don’t have time to grab a camera.
This year, because the time change now happens later than it used to, the effect happened as I was at my desk with a camera handy. It was a rush to snap these images – and I’m sure Junkii would have done a better job – but it will at least give you an idea.