Light Up My Life

October 19, 2009

Old house
Creative Commons License photo credit: Tony Wan Kenobi

Having recently moved, I found myself thinking about all the stuff we accumulate through our lives. And all the time and effort it takes to box everything I own and move it a few miles, just to unpack it all. All good things must end and some things are left behind. I thought of all the things I would be leaving behind, such as the refrigerator, microwave, washer and dryer, and light bulbs. Then I got to thinking about how much energy and money I could save if I had only energy efficient light bulbs.

Light bulbs are not the most important things in the world. Few of us move them from house to house, or even think about them as long as they work, but we have all made pilgrimages to the store solely to satisfy our light dependent needs. Lighting makes up  8% of a household’s electric bill. So what are the different light bulbs available? Which one uses the least energy? Or produces the most light?

Light Bulb
Creative Commons License photo credit: Jeff Kubina

First is the incandescent light bulb. It is the one that most people use.  This is much the same as when it was invented by Edison. It works by running an electrical current though a filament. When the filament gets hot enough, it produces light. It comes in lots of shapes and sizes (and appears over your head when you have a good idea) and uses different amounts of electricity.

Compact Fluorescent lights (CFLs) are fluorescent lights that have been created to be used in light fixtures that use incandescent bulbs. They work by running an electrical current from the ballast (the part that has the circuit board and transistors) and through the mercury vapor which emits ultraviolet light. When ultraviolet light goes into the tube it creates visible light. These create a lot more light at lower wattage and last longer then the incandescent bulbs

Creative Commons License photo credit: Myself248

The third type of light is the light emitting diode (LEDs ). They work by using the principle of electroluminescence in which a semiconductor diode has an electrical current run through it and the electrons are able to recombine with the electron holes to produce light. If you’re like me and don’t understand that, when the switch is turned on, the light also comes on. The LEDs use less power then the other two and will last much, much longer (possibly 100 times longer then an incandescent bulb), but they also cost a lot more.

So now its math time!

A 60 watt incandescent bulb will emit 890 lumens (a measurement of light ) for 750 – 1000 hours and costs $0.75 a bulb.

A 15 watt CFL will emit 900 lumens for 6,000 – 15,000 hours and costs $3.

A 13 watt LED will emit 900 lumens for 25,000 – 100,000 hours and costs $50.

That means a CFL will use 1/4th of the electricity of an incandescent bulb and last at least 12 times as long (6,000/750=8; 15,000/1000=15; 6,000/1,000=6;1 5,000/750=20; 8+15+6+20=49; 49/4=12.25,) so for every 12 incandescent I have to buy one CFL (12*.75=9.) I would save 6 dollars from not having to buy more light bulbs.

Does the same hold true for the LED? Lets find out.

The LED uses 2 watts less then the CFL and lasts 5 times longer (25,000/6,000=4.16r; 100,000/15,000=6.6r; 25,000/15,000=1.6r; 100,000/15,000=6.6r; 4.16+6.6+1.6+6.6=18.36; 18.36/4=4.59.) So I have to buy 5 CFLs for each LED (5*3=15.) I would be losing 35 dollars if I bought just the one LED.

So how much energy can I save?

An incandescent bulb can use 52,500 watts or 52.5 kilowatts over its life time.

A CFL can use 157,500 watts or 157.5 kilowatts over its life time.

A LED can use 780,000 watts or 780 kilowatts.

So if one CFL is equal to 12 incandescent then I would use 157.2 kilowatts instead of 642 kilowatts.

And with electricity being $0.14 a kilowatt hour in Texas (see my previous post ) then I can save (642*.14=89.88; 157.5*.14=22.04; 89.88-22.04) $67.85 in electricity by buying the CFL over the incandescent.

Since one LED is equal to 5 CFLs I could use 780 kilowatts instead of 787.5 kilowatts. I would be saving $1.05 in electricity.

So does this mean the CFL is the perfect new light source? Nope. CFLs use a very tiny amount of mercury (3-5 mg) vapor in each lamp. Most countries have a recycling program set up to help safely dispose of them (in the United States Home Depot offers a recycling program.)

Now that you have read the blog (and become a light bulb expert) which light bulb will you choose?

Authored By Daniel Burch

An inveterate punster, amateur chef, and fencer, Daniel B has a double degree in History and Museum Science from Baylor. He currently serves as the Assistant Program Coordinator for the Wiess Energy Hall and Adult Education at HMNS.

One response to “Light Up My Life”

  1. pgepps says:

    I’m going to stick with incandescents. Flourescent lights, in addition to having various toxic chemicals, give off an unpleasant light and flicker. Fractional cost differences aren’t worth headaches and difficulty reading.

    I use LED flashlights, though, when battery life is the issue.

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