For many years I have been using those “soft white” bulbs that never seemed to give anything else than “dull yellow” light. The only reason I bought them was they were really cheap at Walmart….ok one more reason was that I was too lazy to check out those other lights on the aisle..and never made any kind of comparison.
I have finally managed to put some numbers to the cost of light from at least two different types of light bulbs. The results (along with some general knowledge stuff) are explained below. Make sure you understand the costs on the graphs below.
20W, 40W, 60W, or 100W? Which bulb will give me more light?
-Ok, first of all, that is a wrong question. The ‘W’ stands for “Watt” (after James Watt of the steam engine fame), which is a unit of energy consumption. It does not tell you how much “light” a light bulb will give you. It just tells you how much it will cost you to use the light bulb.
So how do I figure out which bulb will give me more light?
-Look for the value under the word “Lumen” or “Lumens”. Lumen is a measure of light intensity or light output. Higher Lumens value implies brighter light. This value is very clearly displayed on all light bulb packages. See the image below.
So what is the right way to choose a light bulb?
This is in fact written on most packages as something like this: “To save energy costs, find the bulb with the light output you need, then choose the one with the lowest watts”. Here is an image showing where this is typically displayed:
What kind of bulbs will give me more Lumens for less Watts?
This is a no brainer. Compact fluorescent (CF) lights (yeah those spiral ones) give a lot more light for much less wattage. Typically a 15W CF light is equivalent to a 60W regular light, a 26W CF light is equivalent to 100W regular light. When I say equivalent, I mean “gives almost the same Lumens value”.
But CF bulbs are damn expensive! aren’t they?
Yeah that’s what I thought, until I ran the numbers myself. In the graph below, I have compared the cost of using a regular bulb against a CF bulb. These calculations are based on a 15W CF bulb (900 Lumens) and a 60W regular bulb (850 Lumens). I am assuming a 4 hour per day use and 10 cents per kWh (kilo Watt hour). I have assumed the cost of the 15W CF bulb to be $5.58 and the cost of the 60W regular bulb to be $0.615 (yeah 61.5 cents). The buying cost of the bulb is reflected in the “year 0″ in the graph. One bulb of each kind is compared:
The graph shows that you will save about $2.13 per year per bulb by using the CF type bulb. If you have about 15 bulbs in your house, you will save about $31.95 per year. The step in the graph for the regular bulb between months 8 and 9 is because the bulb reached it’s rated life (usually 1400 hours) during that time and a regular replacement bulb was needed which resulted in additional costs. The rated life of most CF bulbs is about 8000 hours so you don’t need to change them for about 5~6 years.
Things become really dramatic when you consider the cost of using 15 bulbs over a period of 5 years. This is shown in the graph below:
For this graph, I have assumed that we changed the regular bulbs every year (you may need to change them more often). In, this case you will end up saving about $480 over 5 years by using CF bulbs. In 5 years, it will be time to change your CF bulbs; but by this time you will have saved so much that this additional cost will not matter much. Also, I am pretty sure that some bulbs get used for much more than 4 hours a day and some houses have many more than just 15 light bulbs
Btw, those cost savings numbers on the CF bulb packaging are not too stretched out; however, they do potray slightly higher cost savings because I don’t think they include the buying cost of the CF bulb in their calculations.
The other good thing I like about these CF bulbs is their “white” light; the “soft white” or yellow light of the regular bulbs is too depressing for me now-a-days.
So what are you waiting for ! Go ahead and get those CF bulbs for your homes right now and start saving money!