Many electrical codes specify a cover over the bulb, to protect you from just such an occurance or the possibility the fairly common occurance of a bulb or tube that vibrates free and drops out.
If the metal portion remained in the socket, then what most likely happened was the bulb's seal failed and enough air mixed into the bulb, while it was off to cause the metal filiment to burn and explosively break free from the rest of the sealant and two thin wires holding it to the metal and feeding power to the filiment.
The two sparks you saw were probably bits of the wire that went through the base to the filiment.
Some other interesting things about light fixtures and lights.
A podium placed directly under a open light fixture is not a good idea
all the "hot air" uhm I mean the speakers voice directly below it tends to vibrate the bulbs out of
thier socket and cause them to drop on the speaker.
Ever wonder why many flourescent bulbs are bare in the fixture?
While Flourescent lights have a significant amount of
mercury and that makes it more important to have a cover in place, most flourescent bulbs will quickly overheat and die or reduce light output if they are
covered.
Those new flourescent curely cue replacements for edison's design are actually worse than edison bulbs by any practical measure, they aren't effective in bathrooms or any location where they need to be turned on and off constantly because that causes them to fail faster than edison's based designs and most standard light fixtures and covers on the ceiling trap the heat and that causes the electronic switching circuits in them to overheat and fail.
LED bulbs are incredibly great long lasting bulb, except all the light circuits where they are used need retrofitted with surge suppressors to gain the long life they claim for LEDs. All is not lost, many homes and business usually have at least one electrical outlet in the same circuit as the room's lighting so it can help to buy a bunch of hopefully cheap surge suppressors and plug them into every outlet to actually get the LED bulbs to last for a few years.
You should also remember that surge suppressors work by sacraficing themselves(thats why most have a pilot light) so you will need to inspect and replace those surge suppressor regularly. I actually personally recommend that any home needs a large number of surge suppressors just for different reasons.
One more thing, if you leave the cover off those curly cue flourescent replacements for edison's designe they can vibrate loose just l ike the edison based designs, but when they break they spread mercury around the room and the recommended procedure for that accident is to remove the floor covering or furniture that has been contaminated and take it to a hazardess waste dump. Naturally you need to follow HAZMAT guidelines when this happens.
Keep looking up
hmelton
Edit forgot to include a columbo joke(one more thing)
