This time of year my everyday commute is in the dark both ways. 1.5 hours in the morning and 1.5 hours at night. I invested in a dynamo hub to power my front main light. I also use a blinking light on my bars. I use 2 different blinking lights on the rear and 1 solid red light. I wear a safety vest and reflective straps on each leg. I use a bar mounted rear view mirror that still doesn't take place of looking back when merging crossing etc etc etc.
Even though I look like a lit up Christmas tree going down the road I ride like I am invisible. At first I was nervous riding in the dark but now with the right equipment and the confidence I am very comfortable at night.
The only time I have had close calls was during the day.
I think a helmet light is a very good idea.