Mr. Electricity is your guide to saving energy in your home.

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How to save electricity on lighting

Lighting is is the third-biggest energy user in most homes.  But it's probably the easiest to save in. You can start saving a whopping 70% right away by siply screwing in new CFL lights. And if you're concerned about mercury if the bulb breaks, you can either use a CFL that has a plastic cover, or use an LED lightbulb instead.  You can also put lights on timers or motion sensors, and just be more diligent about turning off lights you're not using.  A single 100-watt bulb left on continuously will run you $11 a month (assuming 15¢/kWh).

Below are several strategies for saving money on lighting.

Use compact fluorescent light bulbs (CFL's).

If you know only a little about CFL's, you've probably heard that they save a little energy but they contain a lot of toxic mercury. But the truth is, they save a whopping amount of energy, and the mercury scare is way overblown. (The median exposure for a broken CFL is 0.07 mcg, while six ounces of Albacore tuna has 48 mcg -- 700 times as much. See this paper by LBL scientists for more.)

Let's start out by looking at the savings you get with CFL's. Right off the bat, you save 70% on energy as soon as you screw them in. Here's a calculator to demonstrate:

But there are still more savings to be had. Brand-new CFL's last 10 times longer than old-style bulbs, and they generate a lot less heat -- which means lower cooling bills.

I have a separate page which covers CFL's in detail, including pro's, cons, how to shop for them, and the real story behind the mercury warnings.

Install a skylight.

Using natural lighting saves a bunch of energy and produces a much nicer environment besides. Modern skylights are available which let in only the light and not the heat.

 

Use a motion sensor for outside lighting

Exterior security lights automatically shut off after 1-15 minutes, so you're not paying to run them all night. Fixtures start at $20 at home improvement stores like Home Depot. Do not that you can't use CFL's in security lights though, because the fixtures cycle a very small amount of voltage through the lights constantly which makes the CFL's die a lot faster.

Exercise: You buy a security light for $20. The light used to be on all night, for 12 hours each night.  Now it's on for about an hour a night.  You're using two 75-watt bulbs in the fixture.  How long does it take for the security light to pay for itself?  (assume electricity costs 15¢/kWh) (see answer)

Old way: 2 bulbs x 75W x 12 hrs/day x 30.5 days/mo. ÷ 1000 w/kW x $0.15/kWh = $8.24/mo.

New way: 2 bulbs x 75W x 1 hr/day x 30.5 days/mo. ÷ 1000 w/kWh x $0.15/kWh = $0.69/mo.

Savings per month: $8.24 - $0.69 = $7.55

Payback time: $20 / $7.55 = 2.6 months

What the hell are you waiting for?

Use a motion sensor for interior lighting.

If you can't remember (or can't be bothered) to turn off the lights throughout your house, a motion-sensor switch will shut them off for you automatically. You can buy motion-sensing wall switches for as little as $10 at a home improvement store.

Use the lowest-wattage bulbs for lights that are always on (e.g., stairways).

Replacing 75-watt bulbs with 15-watt bulbs reduces energy usage by 80%.  Replacing them with CFL's or LED lights saves even more.

Exercise: How much do you save in a year by replacing a 75-watt bulb with a 5-watt bulb, for a light that's on 24/7?  Use 15¢/kWh for the cost. (see answer)

Old way: 75W x 24 hrs/day x 30.5 days/mo. ÷ 1000 w/kW x $0.15/kWh = $8.24/mo.

New way: 5W x 24 hrs/day x 30.5 days/mo. ÷ 1000 w/kWh x $0.15/kWh = $0.55/mo.

Savings per month:$8.24 - $0.55 = $7.69   (93%!)

Put nightlights on photosensors.

You can get a simple screw-in photosensor for $4.50 ($8.50 for the outdoor version) which will automatically turn your light on at night and off during the day. You just screw the special socket into the existing light socket, then screw the light bulb into the special socket.

Exercise: How long does it take for one of these $4.50 devices (indoor version) to pay for itself, assuming you were using a 60-watt bulb, paying 15¢/kWh for electricity, and saving 12 hours per day of light use? (see answer)

Old way: 60W x 24 hrs/day x 30.5 days/mo. ÷ 1000 w/kW x $0.15/kWh = $6.59/mo.

New way: 60W x 12 hrs/day x 30.5 days/mo. ÷ 1000 w/kWh x $0.15/kWh = $3.29/mo.

Monthly savings:$6.59 - 3.29 = $3.30/mo.

Payback time: $4.50 ÷ 3.30 = 1.4 months

You can also make lamps or other devices go off during the day and turn on at night by using a plug-in light sensor ($6). You plug the appliance into the sensor, and then plug the sensor into the wall. If you're handy with electrical wiring, you can mount a light sensor to a wall (like you'd mount a light switch or electrical outlet). Wire-in sensors are around $10.

Turn off lights when you're not using them, even for just a few minutes.

The idea that lights use extra electricity to start up is a myth. You'll save electricity every time you turn the lights off, no matter how short the off duration, and whether they're regular lights or fluorescents.

You might have heard that you wear out your lights quicker by cycling them off and on, but that effect is so small it's not worth worrying about, and you can safely turn your lights off every time you leave the room, no matter how short the duration. If you feel you need to obsess over this (as evidenced from all the email I get about the subject) then see my answer about fluorescent cycling costs.

Replace fluorescent magnetic ballasts with electronic ones.

For long-tube fluorescent lighting (as opposed to screw-in compact fluorescents), an old-style magnetic ballast might use 100W to power two 40W tubes, while an electronic ballast might use only 60W. Also, the electronic ballast eliminates flicker and usually eliminates hum. They also generate less heat, which saves additional money on cooling.

 

Use LED holiday lights.

LED Christmas lights use 80-90% less electricity than standard holiday lights (which use 25 watts in a typical 50-bulb strand). LED lights also generate much less heat, so they're less likely to catch your Christmas tree on fire.  Another advantage is that the LED's are virtually indestructible -- they don't burn out like normal bulbs (not for about ten years, anyway), and they're not fragile like normal holiday lights. I actually unsuccessfully tried to crush one by standing on it on a concrete surface. I broke the decorative casing but was unable to break the LED bulb itself -- it still shone when I plugged it back in.

I put a few strands of LED Xmas lights on the ceiling and use it as mood lighting.  (Yeah, I know the packaging says not to use them for permanent installations, but that's just how I roll.)

Inirgee sells a nice variety of LED lights in a variety of colors: 120V holiday light strings, and 12V holiday light strings to be powered from a battery. Notably, most of the products carry a lifetime warranty.

We have a separate page about rewiring Christmas lights to run off batteries.

 

Use new LED lighting where appropriate

LED's are the wave of the future.  They use even less energy than CFL's, they last forever, and they don't have any toxic mercury.  (The mercury scare with CFL's is overblown, but still, no mercury is always better than a little mercury.)  LED is going to be the primary lighting method some day.

But LED's come with some big drawbacks, so they're not for everybody, yet.  The downsides are:

1. They're crazy expensive. We're talking $50+ per bulb.
2. They send light in only one direction, so bathing a room in light is impossible (unless you use lots of bulbs).
3. Most models put out a cold, bluish light, rather than the warm, yellowish light of a regular bulb.
4. Most models don't put out nearly enough light.  And those which do are the most expensive.  And manufacturers often exaggerate the output of their LED's. (source)  (When shopping, note that a standard 60-watt bulb is 850 lumens.)

Here's where LED lights currently make sense:

1. Christmas lights.  Just plug in a set of LED's and immediately save 80-90% over regular Christmas lights.  And regular Xmas lights are fragile, but a good set of LED's will last forever.  And at $15 for a set of 70, it won't break the bank.  I use LED Christmas lights as mood lighting when I don't need a whole lot of light.  I hung a couple of strands from hooks aroundthe perimeter of my ceiling. Yeah, the note that came with the lights said "This seasonal use product is not intended for permanent installation or use," but I guess I live on the wild side.
   
   
2. Landscape lighting.  Landscape lights don't need to be super-bright, so LED's work well here.  And they use so little energy they can be recharged by a little built-in solar panel.  Also, they don't need to be as bright as indoor light so the cost isn't prohibitive.
   
   
3. Always-on lights.  For lights that are on continously, 24/7, the energy savings will quickly pay for the cost of the light.  Even if the bulb costs $50.  As the table below shows, the sample cost for an always-on light for five years (including the bulbs) is $680 for incandescent and ~$175 for either LED or CFL.  (CFL's use more energy than LED's but they're cheaper, so the total cost comes out the same).
   
   
4. Installations with lots of bulbs.  Commercial users know that paying staff to constantly change dead bulbs is expensive -- especially when those bulbs are in hard-to-reach places.  But with a typical 25,000- to 50,000-hour life, the labor savings from not having to replace dead bulbs helps offset the labor cost.
   
   
5. Accent / Mood lighting.  If you like your light to shoot straight down (like a spotlight) rather than to bathe the room (like a flood), then LED's can work nicely, though they'll come with the hefty price tag.
   

Here's how the various lighting technologies stack up:

Types of Light Bulbs Compared
	Incandescent	CFL	LED
Watts	100	25	13
Life (hours, typical)	750-1000	4000-10,000 more on CFL lifespan	25,000 more on LED lifespan
No toxic mercury	✓		✓
Price	$0.50	$2.50	$50.00
Cost to run continuously (including replacement bulb costs)
One year	$136	$35	$67
Five years	$680	$177	$173
Ten years	$1360	$354	$345
Cost assumes 15¢/kWh.  Life varies per model. LED life is typically overrated. See How to Misquote this Website.

Color temperature refers to whether the light puts out an orange-ish or bluish light ("warm" and "cold", respectively).  Most LED's seem to be the less popular cold light, and many (most?) manufacturers don't even bother to tell you the color temperature, because if they gave you any clue as to how cold and harsh the light is you probably wouldn't buy it.  If you're shopping for lighting and you want warm light, look for a color temperature of 2700-3000K (not the 3600-5500K of cold light).

Most online stores don't even bother to tell you how bright their LED bulbs are, in either lumens or incandescent watt equivalents, because they probably figured that if you knew how dim these bulbs were there's no way you'd buy them. One exception is the EvoLux which is the first 100-watt equivalent LED light. Unfortunately the quality is just not there yet. The $85 bulb I purchased pointed the light straight down, rather than bathing the room in light like my CFL.

Another rare company to list their LED bulb output is C. Crane. Unfortunately, the biggest bulb in their catalog is only 520 lumens, compared to the 850 lumens you'd get from a standard 60-watt bulb (or a 15-watt CFL). Plus, the bulb costs a whopping $70, and it's a harsh cool white, not warm white.  They do sell a warm white bulb for $45, but it puts out half as much light as their already anemic 520-lumen bulb.

The Simple Dollar has a great review of LED light bulbs.

Related pages:

• Questions I've received and answered about how saving electricity on lighting
• Compact fluorescents -- pro's, cons, and the real story behind the mercury warning