Maybe the passenger had had enough of flight attendants who insist on turning off your reading light when you're asleep, so he decided to make sure of light by leaving the shade up.

Some of us need to have some light all the time, not because we're afraid but because of our metabolism. I have slept with the light on for more than 20 years. I am never in the dark. This means that the secretion of melatonin which is triggered by the light-dark cycles normally never happens to me. (One the rare occasions when it does - thanks to the busybody flight attendants - I feel very sick.)

Quite apart from the beneficial effects on the pigmentation of my skin (I used to get sunburn without even going out in the sun), it also means that I have virtually no problems with jet-lag - ever. Quite important for someone who goes back and forth across the Atlantic regularly.