Worker with Flashlight
This one might seem an obvious one where a white 0201 SMD LED gets attached to a figure's hand. Except that raw LEDs make poor flashlights, which are highly directional. The ideal way to simulate a flashlight is with fiber optics, because fibers are highly directional. The neat thing about using a fiber is that it shines a very convincing glow on the object to which it's pointed.
In this case, I wanted a figure crouched in front of the relay cabinet for a railroad signal, using a flashlight to illuminate the dim interior. The figure I used is actually a painter from Preiser set 79176; the brush he's holding became the mounting point for a single 0.025" fiber, which I painted with black acrylic paint (solvent-based paints can attack the plastic fiber). The fiber ducks underground and is coupled to a warm white 5mm LED: I drilled a hole in the dome and glued the fiber into it.
I only wish the guy wasn't at the back of the diorama, but I didn't have much choice; still, he's only about 9 inches away.