The switch to Daylight Savings time has dramatically altered the ride to and from work. Prior to last weekend, I was running my powerful lights in the morning and rode home in low sun. It's now reversed; low sun in the morning (or dawn, depending on when I get moving), and darkness on the way home.
After a close call or two last year, I run lights if the sun is at all low on the horizon. At night, lights are obviously necessary, but I think they are even more important in low sun. I generally use the "flash" setting front and rear at dusk and switch to steady beams after dark. The trick in twilight is to catch the attention of drivers and pedestrians; at night it's more about being visible and being able to see.
As I have said earlier, there is something magical about riding a bike in the dark, even if it is in rush hour traffic.