Since I am in a smaller boat that is easy to fall out of, when we are running at night I have everyone wear an inflatable PFD, with one of these Glo-Toob lights on it. I discovered them in my scuba days. They are waterproof to 11,500 feet and indestructible. They use an encapsulated LED, have a few flash patterns, and run for over 30 hours on one battery. There is also a power saver mode that will run for about a week. You can find them online for around $20 and they are about the size of your thumb. I always have one close by. On the steady burn mode you can use them for walking and they make a good tent light.
I buy a lot of stuff from the military and I got a huge case of expired Cyalume personal marker lights. The ones in the black tube with the handle that helps you activate it. I don't know the model number but they are the ones you always see on life jackets. Anyhow once they are more than 2 years expired there is a HUGE Difference in light output. Some of the ones that were 5+ years old, just glowed enough to barley notice them. So the advice on watching the expiration date is solid.
Bob