There are a number of stories on the web about the fear factor involved with climbing the cables. I think the story that best illustrates what to expect is
this one from 1999. The guy who wrote it really captured the experience. I recommend anyone going on this hike to read it first, although it's a bit long of a read.
More from my experience:
I made the mistake of wearing a waist pack. The hip mounted water bottles kept getting caught on the pack straps of the hikers coming down while I was climbing up. Another scary sight was someone above me losing their grip and being caught by another person. Then there was a "look out" shouted by someone above, which was soon followed by a water bottle tumbling past. So many people crowed together like a line of ants made progress slow. At some point I lost my fear of heights and could look off to the sides. My arms were weak and trembling from pulling myself up. I was very relieved to finally reach the top. I laid down for about an hour to recover. There is no shelter on top so basically I baked for an hour an 8800 feet. Strong sun screen is a must. After l looked around the top I started my decent. By this time it was approaching evening and I almost had the cables to myself. I had about two more hours of daylight remaining. On the trail back I ran out of water, and luckily I found a half full water bottle someone had dropped. I was really dehydrated. If I did this hike again I'd stash some water off the trail just below quarter dome.
In contrast, some other people just zipped up and down the cables with ease. Some impatiently going outside the cables where there are no log steps for footing.
Getting back on topic; just about any light will be fine for hiking down. The blue 3mm LED in the cheap laser pointer I had did the job ok. I just wish it had a constant on as I continually had the hold down the momentary button.