LED's (or Light Emitting Diodes) are bright, but use very little power compared to ordinary bulbs. They produce very low amounts of heat, are impact resistant, and their average lifespan is around 100,000 hours - much longer than ordinary bulbs. In recent years the costs have come down as well, so they are also now cheap enough to use for normal domestic lighting.
One thing I did notice with the ST1100, was that the instrument panel lighting wasn't that good. I therefore purchased some high-powered blue LED 501 bulbs and installed these (they were a direct fit, no modifications were required). The instrument panel now produces a blue glow making the instruments very easy to read at night. And in my opinion it looks good as well!
LED bulbs are also available as stop-and-tail lights (see High Level Brake Lights ) and even indicator bulbs. However, if you are replacing your standard turn signals with LEDs, you may need something called a load equaliser to prevent your turn signal from flashing too quickly - unless your LED bulbs have a built-in equaliser, of course.