Incandescent vs. CFL Bulb - Electricity Analysis


We have been analysing the electricity consumption of incandescent light bulbs versus CFL light bulbs in our apartment.

We are getting ready to do the same analysis again, this time using LED light bulbs. LED light bulb prices are coming down, but more importantly the LED fitting sizes, the requirements for light warmth and the ability to direct the light according to each locations application are finally available.

In our previous article - Incandescent versus CFL - we published a detailed graph showing the moment by moment difference in the amount of electricity used. In this article we are going to compare the actual electricity used by my wife and I each day. Monday and Tuesday were measured using the old incandescent light bulbs, Thursday and Friday were measured using the new CFL light bulbs.

It is one thing to say that the CFL bulbs use 75% less electricity. This data has allowed us to see how much electricity WE practically do save each day - and is it worth it.

Update: Jan 2012 - We are expecting to replace the bathroon CFL bulbs soon - they are turned on many times each day - see our post How Long Does a CFL Last - and are taking progressively longer to reach full intensity.

Here is the graph of actual electrical use for our light bulbs - measured using a watts up Smart Circuit 20

X Axis - Time
Y Axis - Watts

I believe we finally have accurate
data that we can depend on!

We are using half the amount of
electricity that we were using.

146 KWh saving per year

$48.94 saving per year
PG&E rate of 0.33518 KWh

CFL's do contain a trace of mercury, see The truth about Energy Saving (CFL) Light Bulbs where we write "but the mercury is sealed within the bulbs glass tube and is of little danger if the bulbs are disposed of correctly. The amount is less than four milligrams, about that required to cover the tip of a ball-point pen.

Individual CFL's have a Power factor of between 55% and 70% (the actual power factor on the circuit during the above testing was 100% for the incandescent bulbs and 85% for the CFL bulbs) If ever there was a confusing topic filled with FUD (Fear Uncertainty and Doubt) this must be high on the list.

See this summary for an explanation of real power, apparent power, reactive power and power factor. The article has a link to Wikipedia for those who want an even more detailed explanation.

CFL’s give off less heat than incandescent bulbs, for the same Lumens of light. This is why they use up to 75% less electricity. If you are in a cold climate, you could argue that the incandescent bulbs are no less efficient for their extra energy will be less heat to create - not sure about this - but worth mentioning!

The combination of a longer life, and the energy you will save justifies investigation into CFL lighting in almost all situations. This is particularly true for outside walkways and home entrance lighting. These bulbs are on for 8 hours each day and I can see no reason not to replace them.

We know that this is a lot to ask - but if you have installed a CFL bulb in your home - and have been using it for one year or longer - please can you share your experience with our readers.


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