BACK IN 1999 I was taking part in a music video being filmed in the Orkney Islands. (Other groups might shoot videos on yachts in the Caribbean; we opted for a fishing boat in Scapa Flow.) I got into a conversation with the man steering the boat, the captain you might call him. It was a beautiful midsummer's evening, a prolonged dusk with the sun refusing to set: "the simmer dim" they call it in Shetland, maybe in Orkney as well.

I made a comment about how lucky he was to live among these islands. "It's hell in winter." He replied, an uncharacteristic bitter tone to his answer. It turned out that during the winter months, he was crippled by seasonal affective disorder - or Sad as it's commonly abbreviated - the absence of sunlight causing anxiety, lethargy and depression in sufferers. The Orkney Islands sit at 59 degrees north (the Arctic Circle sits at 66 degrees), so in the winter months, the islands can get as little as five hours of weak grey light a day, and if the weather's bad, which it often is, it can feel like constant darkness. The further north you travel, through the Shetland Islands on to the Faroes and Iceland, the light gets less and less until you reach the Arctic Circle and it's a full 24 hours of darkness in winter. If you're prone to Sad, this is not the place to be living.

How this otherwise-cheery captain suffered he didn't let on. It was hard to imagine. He and his wife seemed such a contented, accommodating couple: her in stars and stripes bandana making everyone tea, and him steering tourists around Scapa Flow in his boat, letting them meet the seals and ogle the shipwrecks poking out of the water, while entertaining indie bands from Edinburgh making music videos.

Down here in Glasgow and Edinburgh it's getting darker earlier, and today especially, with the clocks going back, it is really starting to feel like winter. There's still (cloud permitting) a good chunk of daylight to get out in though, so plenty of opportunities to boost the serotonin and vitamin D supplies. It's difficult to imagine not having any daylight at all. For months. Or suffering a serious disorder because of it. In the past I've tended to romanticise dark winter days, imagining life as an Arctic recluse: reading difficult novels by the fire, whittling wood, or using the time to learn to play the piano or speak Spanish. I realise the reality is more like never leaving bed unless it's to pour yourself another double brandy, or watching the shopping channel for 18 hours a day while gorging on chocolate bars in between sobbing fits. You're living life under an immovable dark cloud with a sense of doom saturating every day. Until spring, anyway.

My only experience of a day where the sun never properly rose and darkness prevailed was on holiday in Iceland in November a few years ago. But the icy cold dark days just added to the magical sense of the place, especially while soaking in the warm milky waters of the Blue Lagoon with the aurora borealis dancing overhead.

There's comfort to be found in darkness, but being denied the power of light is another thing entirely. You've got to think this relationship with light and dark - long summer nights and cold, dark, gloomy winters - has partly shaped the character of the Scots. It's certainly made its impact on the landscape. Glencoe in a midwinter storm is about as intense and moody as it gets, contrasted with the calm, gentle beauty of a midsummer's evening in Orkney.

Weather-wise the Scots never know what they're going to get, but are conditioned to expect the worst - Sad being the nastiest result of this inevitability. Even in the face of this, though, I still prefer it to living some place where the weather and the seasons stayed exactly the same, sunshine day in, day out. Apart from anything else, I'd have nothing to talk, or moan, about.