The electrical energy that is used by light bulbs is converted into about three different kinds of energy. They are light energy, heat energy and sound energy.
Light energy is what we want, so let’s focus on the other two.
Yes, sound from light bulbs is wasted energy.
Do you ever listen to your lights? When I say lights, I am including the fixture, ballast or electronics package, if any, along with the bulb.
When you hear a light that is making sounds, you are hearing wasted energy. The buzzing, humming or whirring noise from lighting equipment is not light energy. It is escaping sound energy.
Fortunately, for those of us who pay the electric bills the energy wasted from lighting as sound energy is very small.
Energy wasted as heat from lights is a big deal.
The really big waste of energy from lighting is heat. Heat is not light. Unless you want it, heat is wasted energy.
Old fashion Thomas Edison style light bulbs make very efficient heaters. These incandescent light bulbs convert about 95% of the electricity they use into heat. Big carbon foot print little light.
That explains why they are so effective at keeping pipes and well water pumps from freezing. You country folk out there know you keep a light bulb on inside your well pump shed to keep the water flowing during freezing weather.
If you need a space heater, in an emergency, plug in as many old light bulbs as you can.
When 95% of the electrical energy is converted to heat energy, it leaves only 5% that is converted into light energy.
The next group of light bulbs I’ll call the 80% heaters.
Light bulbs that operate at very high temperatures are about 80% or more efficient as heaters.
Halogen lights like the headlights on cars.
HID lamps (High Intensity Discharge) used in street lamps.
Mercury vapor lights, like some folks use as yard lights.
These light bulbs put out a lot of light. To do it they operate at very high temperatures. They are OK to use outdoors or in big buildings but not so safe in homes.
When they convert about 80% of electrical energy into heat, it leaves only 20% that is converted into light. Better than the incandescent bulbs but still not wonderful. They save money only because they last a lot longer than incandescent bulbs.
The surprise to many people is that LED light bulbs convert about 82% of the electrical energy into heat. They don’t get very hot because they are designed to cool quickly.
The long life of LED lights depends on keeping them cool. The electronics package hidden in the base of the bulb will melt down if it gets too hot. That is why you can’t use them in your oven. They would last a very long time as the light in a refrigerator.
When they convert 82% of electrical energy into heat, it leaves 18% that is converted into light. The good thing about LED bulbs is they give a lot of light for a small amount of power and last a longest of all, so far.
The other good thing about LEDs is they do not contain mercury.
So what kind of light bulbs are the worst heaters?
Fluorescents are poor heaters in that they only convert about only 30 to 50% of the electrical energy they use into heat. Did you ever try to keep warm by huddling around a fluorescent light? I didn’t think so.
Because they are such poor heaters, they save money on electrical bills two ways.
First, they put out the most light for the electricity used. This is why Compact Fluorescent Lamps (CFL) are so popular for home use.
Second, because they don’t create as much heat they also reduce air conditioning bills. The heat from lighting is part of the heat load that your AC works hard to remove from the building. Less heat load means lower air-conditioning cost.
I know some folks who use incandescent bulbs at home in the winter, when heat is a good thing. Then they switch to CFL bulbs in the summer when heat is not wanted.
They are right about the home heat loading.
Their bulb switch plan is good because it exercises your wrist muscles with all that twisting in and out of light bulbs. It is also good because you wipe away the dust that blocks some of the light from your bulbs twice a year.
I don’t do this because whenever I juggle light bulbs, some of them get broken.
Fluorescent lights are good because of their small carbon footprint, but they do contain trace amounts of mercury. Pick your poison. The amount of mercury in fluorescent bulbs has been minimized as they have evolved over the years, but it is still in them.
Disclaimer: The percentages given above are really well rounded off to keep this article short. Please don’t get lost in the numbers. Some science folks would argue that the light energy from electric lamps is converted to heat energy as it bounces around our rooms. So, all light bulbs produce 100% heat, eventually. I just put that in here to give you something to stew about.
by Birney Summers – 2009 All Rights Reserved