LED technology is a huge step forward in lighting, primarily in dependability. For all practical purposes, you can forget about spare bulbs, and you will get much longer run times from LEDs, compared to incans. This means that batteries, and hence, lights, can be much smaller and still be practical.

When caving back in the days of incandescent lights, I would follow the standard directive and have three separate sources of light, all of which were fairly bulky and not really all that reliable. Nowadays, I often routinely EDC at least three sources of light - a AAA keychain light, a small AA on my belt, and at least one photon style clipped somewhere on my backpack or briefcase. All of them together are less bulky and lighter than just one of the C or D powered incans I used to carry, are more dependable, just as bright, and have longer run time. I wouldn't hesitate to use either the AAA or the AA on an all night hike, if necessary.

There are improvements in batteries and the build qualities of the lights themselves,so that lights now are light years ahead of those available only a few years ago.

LEDs are replaceable with some difficulty. There is a whole section of flahlight "modding" over at candlepower forums, well
worth a visit. There are also retrofit LED modules for upgrading popular incans,like Maglites. These are the ones with the two pin connectors. They are often a practical way to upgrade a favorite old light.

There are several different types of LEDs on the market and it is a rapidly changing technology. The newest offerings are considerably brighter with the same run time than what was available only a few years ago. The candlepower dudes track and discuss these developments endlessly. They are just as compulsive as we are.