I was running late for work this morning. Very late. As I arrived at the station I was reminded why I prefer to be in work for 8 a.m. rather than 9 a.m. The platform was thronging with people and it seemed unlikely that I would be able to get on the next train, let alone find a seat. Following a sleepless night and a queasy breakfast my journey into work was resembling more a test of endurance than its usual ten minutes checking emails and twenty minutes reading The Economist. There was an instant, I admit, when I contemplated turning on my heel, walking back to my flat, and cocooning myself in my duvet. But I didn't. I waited three minutes for the next train.

To my surprise, and doubtless that of every other person waiting, the next train that rolled in was half empty. I sat down, tried to ignore the unpleasant amalgamation of stale sweat and last night's alcohol emanating from the gentleman sitting next to me, deleted a writeup, and replied to my brother's email reminding me to book tickets for a concert in September. And then it went dark. Not the-sun-has-disappeared-behind-a-cloud dark, not my-eyes-must-adjust-to-being-in-the-tunnel dark, but we've-just-entered-a-tunnel-and-nobody-has-switched-on-the-lights dark.

Not one light was burning in the train.

No one groaned, no one sighed, no one muttered. There was no jostling, no fidgeting, no pushing. The train was in a state of perfect calm. A few people did attempt to read by the backlights of their mobile phones, or to illuminate the small area of the train where they were sitting or standing, but soon stopped. Maybe they sensed it was futile, or maybe they realised that there was a rare moment of peace to be enjoyed on the London Underground. Then, the only light came from the streaks thrust into the blackness by the occasional train passing in the opposite direction.

At Liverpool Street the driver was notified that he had forgotten to illuminate his carriages. The lights flickered on, ushering us back into our over-crowded, overheated, over-irritated normality. But those of us who had enjoyed the darkness retained a precious filament of tranquility. It didn't matter that I was late, or that I was tired, or that I dislike the new office; I'd experienced something unusual and my day was brighter for the black.