A Tale of Two Light Bulbs

Incandescent or Fluorescent?? The story behind them represents the dilemma faced by renewable and efficiency proponents in today’s marketplace. You will be faced with an energy quiz almost everyday for the rest of your life. This tale is an example of one of the choices you’ll be asked to make. What kind of light bulb should I buy?

Background of Energy Use in Lighting Technologies  Amount of light given off by a light bulb is measured in lumens. One lumen is equivalent to the light given off by one candle. A watt is the amount of electricity a light bulb uses to produce light – it is not an indication of brightness. This is important to note because a 13-watt compact fluorescent produces as much light (lumens) as a 60-watt incandescent bulb. Using only a quarter of the electrical energy.

Incandescent or Fluorescent?  On this side we have a 100-watt incandescent bulb just like we all have in our houses.  It’s what we use to light our houses.  This light produces 1,690 lumens of light.  On this side we have a 23 watt compact fluorescent bulb.  It is similar to the tubular fluorescents in most classrooms, but it kind of “twisted” into a smaller package and it screws into a standard socket.  This light bulb produces 1500 lumens of light.

Let’s find out! So what exactly is the difference between these bulbs? How could a 100W incandescent bulb produce about the same amount of lumens as a 23W fluorescent? Incandescent or Fluorescent?

Incandescent…  very thin tungsten filament that is housed inside a glass sphere.  come in sizes like “60 watt,” “75 watt,” “100 watt”  Electricity runs through the filament, since the filament is so thin it offers a good bit of resistance to the electricity.  This resistance then turns electrical energy into heat.  The heat is enough to make the filament white hot and the “white” part is light.  The filament literally incandesces because of the heat.  Heat is not light and the purpose of the light bulb is light, 90% of the energy is spent creating heat.

Fluorescent…  In fluorescent bulbs there are electrodes at both ends of the tube and a gas containing argon and mercury vapor within the tube.  A stream of electrons flows through the gas from one electrode to the other.  These electrons bump into the mercury atoms and excite them.  As the mercury atoms move from the excited state back to the unexcited state, they give off ultraviolet photons.  These photons hit the phosphor coating inside of the fluorescent tube, and the phosphor creates visible light.  The phosphor fluoresces to produce light.  A fluorescent bulb produces much less heat, so it is much more efficient.  Fluorescent bulbs are 4 to 6 times more efficient than incandescent bulbs.

Would you pick one of these up off the ground??

Of course you would! Changing your light bulbs to fluorescent bulbs is the same concept. How? – Well let’s do the math.

Here’s the details… Incandescent (Standard) vs. Compact Fluorescent Light Bulbs (CFLs) Bulb Type 75W Incandescent20W CFL Lumens Produced 8301,200 Purchase Price $0.75$5.00 Number of Hours Burned per Day 4 hours Life of the Bulb 750 hours or ½ of 1 year8,000 hours or 5.5 years Number of Bulbs Needed to equal life of 1 CFL/Total cost of those bulbs ~11/$8.251/$5.0 Total Cost of Purchasing Bulbs $8.25$5.00 kilo-Watt hours (kWh) over the 5.5 years 75W x 750 hrs = 56,250 Whrs 56,250/1000 = kWh kWh x 11 = kWh 20W x 8,000hrs = 160,000Whrs 160,000/1000 = 160 kWh Total Cost of Electricity for 5.5 years (8 cents x kWh) $49.50$12.80 Total cost over the 5.5 years $57.75$17.80 Total Savings using a CFL compared to an incandescent bulb: $39.95

Environmental Concerns  A single 20W compact fluorescent lamp used in place of a 75W incandescent bulb will save 550 kilowatt- hours over its lifetime.  If the electricity is produced in a coal-fired power plant. The savings represent 500 pounds of coal not burned, which means 1,300 pounds of carbon dioxide and 20 pounds of sulfur dioxide will not be emitted into the atmosphere.

In conclusion…  The savings are well worth the initial expense for buying a compact fluorescent.  So, talk to your parents about the cost savings of switching from incandescent light bulbs to compact fluorescent light bulbs, it is well worth it in the long run.  There is much less waste by using compact fluorescent bulbs in terms of energy waste, actual waste and emissions into the atmosphere.