Should I Switch to Dimmable CFL Bulbs?


Dear Pablo: We have 12 recessed light bulbs in our kitchen on a dimmer switch. How much money and energy we would save if we switched to dimmable CFL bulbs? They would have to be cost effective because cash is tight these days.
According to USA Today, in 2007, CFL bulbs held a 20 percent market share in the United States. While this is up 9 percentage points from the previous year, we've still got a long way to go. Aside from the obvious lack of awareness and the persistent stigma around the quality of fluorescent light, light fixtures that are on dimmable circuits may pose a barrier to even the most environmentally conscious households. The good news is that there are dimmable CFL bulbs, the bad news is that they are far more expensive than regular CFL bulbs.

The Story of CFL Bulbs

When CFL bulbs became publicly available they were bulky and dim, flickered, and produced harsh light. Since then, these curly bulbs have come a long way. Fluorescent bulbs are now available in different color temperatures, ranging from the cool white of an operating room to a warm white that mimics incandescent bulbs. You can even find yellow bug lights and black lights in specialty lighting stores. CFL bulbs now use a high frequency ballast that eliminates any visible flicker and some bulbs are now compatible with dimmer switches.

Replacing Incandescent Bulbs with CFL Bulbs: Looking at the Numbers

First of all, lights on a dimmer do use less electricity when the light is dimmed, almost proportional with the brightness. So a 100 Watt bulb turned down halfway will use a little more than 50 Watts. Keeping the dimmer turned down, or the lights off completely when not in use is a first step, but CFL bulbs will save you 75 percent on top of that.Let's assume that you use your kitchen lights for one hour in the morning before work, and three hours in the evening for cooking, eating, and clean-up. Let's also assume that you are currently using 100 Watt incandescent bulbs. This amounts to 4.8 kWh (kilowatt-hours) per day. Assuming your utility company charges $0.12 per kWh, you're spending $0.58 per day, or $210 per year to light your kitchen! Not only that, but you're also producing about a ton of greenhouse gas emissions per year (depending on where your utility's electricity comes from). The equivalent CFL bulbs use only 23 Watts so you will be cutting your daily electricity use to 1.1 kWh and your annual electricity expense to only $48--that's a $162 savings. Bulbs.com sells 23 Watt dimmable CFL bulbs for $8.99. At this price you can replace all of your bulbs for $108, with a payback period of 8 months.But that's not the end of it. I assume that a big reason your kitchen lights are on a dimmer in the first place is that 12 bulbs at 100 Watts each is a lot of light! So another option is to install non-dimmable CFL bulbs equivalent to a 60- or 75-Watt incandescent (look for CFLs with between 900 and 1,200 Lumens) and replace the dimmer switch with a regular toggle. A 60 Watt-equivalent CFL bulb uses only 15 Watts and costs about $3, or only $36 for your whole kitchen. Your annual energy use will now cost you only $32--an annual reduction of $178--with a payback period of just 9 weeks.

How to Calculate Your Savings When Switching to CFL Bulbs

To figure out how much money you'll save by swapping in a CFL in your home, first determine the wattage of your current incandescent bulb you'll replace. Next, find a CFL with equivalent wattage. Estimate the number of hours per day you use the light then check out the electricity rate on your latest utility bill. Finally, perform the following calculation using the wattage of the current bulb, and again for the new bulb. The difference between the two results will be your annual savings:
(Bulb Wattage x Hours per Day) / 1000 x Electricity Rate x 365



Ask Pablo is a weekly column that aims to answer your pressing eco-quandries. Want to ask Pablo a question? Simply email Pablo(at)treehugger(dot)com. Wondering why Pablo's qualified to answer? As the VP of Greenhouse Gas Management at ClimateCHECK, he helps major corporations measure and manage their greenhouse gas emissions.


Additional Resources on CFL Bulbs

Ask TreeHugger: Is Mercury from a Broken CFL Dangerous?
CFL Bulbs or Compact Fluorescent Light Bulbs: Energy Savings, Mercury, Recycling and More
CFLs Could Curb Global Lighting Demand by 40% - and At What Cost?
Recycle Your Compact Fluorescent Light Bulbs with Ease
TreeHugger Forums: New CFL Options
Green Basics: Compact Florescent Light Bulbs

Previous Ask Pablo Articles on CFL Bulbs

Ask Pablo: Mercury in CFL Bulbs
Ask Pablo: LED Light Bulbs
Ask Pablo: Should I replace my bulbs now or wait until they die?

Tags: Compact Fluorescent Light Bulbs | Electricity | Energy Efficiency

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