I Thought I Had An Idea

Q: dear 100 board
i apologize for my absence, but i need an answer and i know of only one place to get the truth..... ok board a light bulb burns out, are we still using energy if the light switch is on even though our bulb has seen its last?... i appreciate your time oh wise 100!!

Pat

A: Oh Pat. Your absence is unexcused. The 100 Hour Board is aware of your departure and responsible for your light bulbs burning out.
The answer is yes and no. Or rather my favorite answer ever...it depends! Depends on what?
It depends on what kind of light bulb you have.

Light Bulb 101:

Light bulb technology is pretty intricate, cool and yet simple at the same time. Makes you respect Mr. Edison more.

Incandescent bulbs (old technology) work by sending a electrical current through a resistor, in this case thin tungsten coil filaments, that resist the flow of electricity and convert it into heat and some light. Only about 10% is visible which is why they are so inefficient. Normally the tungsten would catch on fire, so they fill the light bulb with argon or nitrogen. Over time the tungsten atoms fly off because the filament gets really hot - 4000 degrees! Like evaporation off water. The argon helps keep this from happening.

But over time, because of the tungsten leaving, and the constant on and off, rapid heating and cooling, the filament gets brittle and breaks. And your bulb burns out. Now an incandescent bulb can also fail because of vibration (filament breaks loose), glass breaking (argon leaves and filament catches fire), or the connection to the bulb and fixture is bad (that solder piece is deformed or the copper spring contact bends in - stemming from over tightening bulbs).

No matter which way it burns out, with incandescent bulbs, no electricity is flowing. The electrical circuit is broken. Like cutting your cord to the lamp. Which is why they are safe to leave in - no electric shocks from probing fingers.

BURNED OUT INCANDESCENT BULB = NO POWER

But fluorescent bulbs use a different principle to operate. A tube of argon coated in phosphor powder, is also filled with a little mercury. Electrodes at either end flow electrons through the plasma in the on tube and this causes gaseous mercury to release electrons and light. Although it releases ultraviolet light. The phosphor powder absorbs the UV and releases white light (or other colors depending on the powder). (I recommend looking at this page at How Stuff Works.)

These lights require a starting mechanism - usually what they call a ballast - that stores and releases energy at start-up. "Burning out" for fluorescent bulbs are less defined if they are not catastrophic (glass breaking) but can include issues with the electrodes, ballasts and leaks.

When fluorescent bulbs burn out it is possible to have electricity flowing through the tube but not igniting the mercury electron release. Also you can be sending electricity to the ballast all the time the switch is on. It could be a slow leak or even more to the ballast.

BURNED OUT FLUORESCENT BULB = SOME POWER

So not only do you need to worry about mercury spills and the EPA with a broken flourescent bulb, you need to worry about stray current! Oh my!
Hope that gives you some answers - or ideas to swallow for that matter:

100 HB
(Top photo courtesy of Josh Madison)