The funny part of the story is that we were only about 50 feet from the trail and probably could have made it back if we had only known!
Now I always carry lights. Lots of lights. In my pack are a headlamp and a cap lamp which clips on to the brim of your cap or hat. I also carry a couple of those little keychain lights that realtors hand out. But wait! There's more. In my pocket I carry at all times a penlight powered by two AA batteries. It gives off usable light for about 24 hours. Then there is the flashlight on my cell phone, and also a little keychain light/tool kit I got at SWISS+TECH.COM which, believe it or not, actually got me down the steep side of Mt. Sanitas in Boulder one summer evening.
Lights are another one of those "effectiveness multipliers" that I mentioned in a previous post. Without a light you are just fumbling around in the dark. With a light you can see what you are doing in a medical emergency as well as give the victim, and yourself, a psychological lift.
One last thought: CHECK THE FREAKING BATTERIES before you leave the trailhead!