How to Calculate the Savings from using Compact Fluorescent Light (CFL) Bulbs

Compact Fluorescent Light (CFL) Bulb

When I was doing the research for our Ultimate Guide to Compact Fluorescent Light (CFL) Bulbs, I put together a short section on calculating the savings for each CFL bulb you installed. In order to make it easier for our readers to find this work, I’ve summarized it here in this post.

Compact Fluorescent Light (CFL) Bulbs will save energy and cut your electric bills. They cost more initially, but will last as much as 10 to 15 times as long as regular light bulbs.

CFL bulbs only need 20-25% of the energy of a normal light bulb, so you’ll save money on electricity. How much money you’ll save depends on how high your bills are already. If your electric bill is $200/month then on average you could save $10-15/month by switching most of your lights to CFL bulbs.

Switching to CFL bulbs is a simple way to play a part in helping slow down global warning. You can save money and feel good while you’re doing it.


According to OSRAM’s on-line catalog, CFL lights can last between 6,000 and 15,000 hours of normal use. That’s over 10 times as long as the expected life of a normal light bulb which is only 700-1000 hours.

How much will you save?

A normal 75 watt bulb priced at an on-line discount website cost 79 cents per bulb. A 6-pack of similar CFL bulbs was available from an on-line discount website for $15.16, or just about $2.50 apiece. Electricity costs are assumed to be about 10 cents per Kw-Hr (you can find your actual electricity cost on your most recent power bill).

Purchase cost per bulb:

  1. Normal Bulb = $0.79 USD (or 79 cents)
  2. Equivalent CFL = $2.50 USD

Electricity cost to use over life time:

  1. Normal Bulb: 75 Watts * 1000 Hrs * 10c/Kw-Hr / 1000 = $7.50
  2. Equivalent CFL: 20 watts * 12000 Hrs * 10c/Kw-Hr / 1000 = $24.00

Cost per year:

  1. Normal Bulb: $7.50 lifetime cost * 1.5 bulbs / year = $11.25 per year
  2. Equivalent CFL: $24.00 lifetime cost * 1/8 bulbs / year = $3.00 per year

In other words, a normal bulb costs $11.25 per year while the CFL costs only $3 per year. Switching to a CFL bulb will pay for itself in under 6 months.

Switching the top 10 lights in your home to CFL bulbs could save you $80/year on your electric bills.

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13 thoughts on “How to Calculate the Savings from using Compact Fluorescent Light (CFL) Bulbs

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