I’m building a new house right now and one of the areas of concern is electricity cost. We use Green Mountain Energy which is 100% wind power. (Yes, I know my electricity comes from the Texas grid which has gas and coal and nuclear plants. However, my money goes to the wind farm, not to the other power sources.)
I’ve been thinking that I want to go pure LED (light emitting diode). There are several reasons. The first is that the run cooler than any other light bulb. At night, in Texas, in the summer, sometimes the temperature almost drops all the way to 90ºF. Believe me, there is a difference between sitting in a room with incandescent bulbs and one with CFLs. The second is electricity cost. The third is using less electricity (related to cost). The final point is that LED lamps tend to run at a higher color temperature. This last may need a bit of explanation.
There’s a concept in physics called a ‘black body’. I won’t go into details, but the frequency of radiation (light) emitted by a black-body depends directly on the temperature (in degrees Kelvin) of the body. So a black body radiator that is at a temperature of 2,000K emits an orangish light, while one at 10,000K emits a bluish light.
Incandescent bulbs emit light between 2,000K and 3,000K. So the light looks orange or yellow to us. These are called ‘warm colors’. It’s an artist thing about how the light makes you feel when looking at it. Yellows and oranges make you feel warm. Contrast that with a light emitting a bluish light which makes you feel cool, like a compact fluorescent bulb. These can range in temperature from about 3,000K to 6,700K.
Sunlight is filtered and scattered in our atmosphere, but a clear day with sun overhead is roughly equivalent to a 6,500K black body. While if you look towards the pole (perpendicular to the sun) on a clear day, you might get all the way up to 15,000K color equivalent.
I live with an artist, so true color is psychopathically important in our house. LEDs and compact fluorescent (and some other fluorescent bulbs) can reach the 6,500K mark. Look for ‘daylight’ bulbs. They are pretty popular now, but make sure it has the color temperature on the label. Some places are selling 3,000K bulbs as ‘daylight’. Here’s a hint, people who grow things that need actual daylight (indoor gardeners and reef aquarium keepers) use lamps at a minimum of 6,700K and all the way up to 20,000K . And, I just prefer cooler light… again that may be just living in central Texas.
Now, how does this apply to light bulbs. The house is LEEDS certified and Energy Star and all that stuff. Some of the LEEDS certification comes from building efficiency, more efficient HVAC systems, better plumbing, more insulation, etc. But part of it is a reduction in the used electricity.
According to several sources, a modern home (within the last 5 or 6 years) will cost up to half as much to operate (heating, cooling, electricity, water) as a house built just ten years ago. Lights are a small part of the improvement.
Think about the room you use most often (kitchen, office, whatever). In my current bathroom, there are 6 60-Watt incandescent bulbs providing light. They are in use about 4 hours per day (me, wife, kid bathing and dressing). That’s
6 * 60-Watts = 360 Watts
* 4 hours = 1440 Watt hours per day
or /1000 = 1.4 kilowatt hours per day.
Times 365 days = 525.6 kilowatt hours per year
at $0.10 per kWh = $52.56 per year in electricity… for that ONE room.
It also makes the room quite warm, which for the 8 days a year that it’s cold in central Texas (and I mean anything below 50°F is cold)*, otherwise it’s just more to cool off. At least one source says that a 100W incandescent bulb hits 375°F. I haven’t tested it, but it seems reasonable to my burned fingers. Compact fluorescent and LEDs just don’t get that hot. They don’t convert electrical resistance to light like a incandescent bulb does. Resistance generates heat. Up to 90% of the electricity going into an incandescent bulb is turned into heat instead of light. For that 100W bulb, you’re getting 10W worth of light and 90W worth of heat.
I haven’t mention halogen bulbs (or any of the other weird bulbs like High Intensity Discharge or metal halide) because they are either way too hot (metal halide and halogen) or need special UV coatings (HID) or they are just not appropriate for home use (sodium vapor). I’ve seen both halogens and metal halides in home use and, no doubt, they pump out light. But they are just so hot.
Let’s talk about light for a second. Light is measured in lumens. A lumen is the total amount of visible light emitted by something. I won’t go into candelas and steradians here. But you can get more at Wikipedia if you like.
When every lamp was an incandescent, it didn’t really matter how they were measured. A 75W bulb was less bright than a 100W bulb. But now that we have all these super-efficient bulbs it makes sense to talk about how much light is actually produced by the bulb.
Now, the industry is using lumens to measure how much light the bulbs produce. A 60W incandescent lamp may push 800 lumens, while a CFL only needs 15W and an LED only needs 10Ws. A 10W incandescent is a night light.
If you are thinking about changing, look at your space and decide if you want more light, about the same, or less light. Then decide if you want warmer light or cooler light. If you have 6 60W bulbs in your bathroom, that’s about 4800 lumens. About 6 10W LEDs will produce the same 4800 lumens.
One note about this. LED lights have two properties that need to be taken into consideration.
The first is that LEDs are highly directional. Unlike incandescent and CFLs, they only emit light in one direction (usually a hemisphere). Even incandescent spot lights emit light in all directions, just some is reflected back by a coating on the glass part of the bulb. So LEDs tend to act as spot lights and, in a certain area, may be brighter than you expect while everywhere else tend to be dimmer than you expect. They are really good for task lighting (and they don’t get as hot).
The second is that LEDs are point sources not diffuse sources like the other light bulb types. You can get some strange effects in water, reflections, and the like with LEDs. If you’ve ever been underwater and seen the shimmer effect that the sun makes in the water, you know what I’m talking about. LEDs do that. It can be unsettling when you first realize it, but you get used to it.
Let’s say that I replace those 6 bulbs in my bath room with CFLs. I need
6 * 15W bulbs = 90W
* 4 hours = 360Wh or
/1000 = 0.36 kWh per day
* 365 days per year = 131.4 kWh per year
* $0.10 per kWh = $13.14 per year
A difference of almost $40 per year in electricity savings. A good CFL will set me back about $4 per bulb (for a really top of the line one). The electricity savings alone pays for the bulbs in less than a year.
Using LED bulbs is roughly the same. You save an additional $4.00 per year, but the bulbs themselves are much more expensive. The prices are coming down though. And they are rated to last 50,000 hours, while CFLs are rated for 10,000 hours and incandescents are rated for about 1,000 hours. To give you an idea, 50,000 hours is 17 years running 8 hours per day. I’ve been in our current house for five years and never replaced the CFLs that came with the house, but I’ve replaced every incandescent bulb at least 3 times.
Here’s my plan for our new house.
The first thing will be to replace whatever lights that are incandescents with either CFLs or LEDs, depending on the function of the light. Bathrooms and general light will be CFLs while task lighting, pendants, etc will be LEDs. As the CFLs need to be replaced, in 5-6 years, I can changes those to LEDs.
The can lights in the ceiling will be replaced with LEDs immediately. First, they need to be spot lights rather than flood lights. Second, can lights run hot anyway and need to be cooler. Third, they are a pain in the ass to replace and I never want to do that again after the first time.
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* Scoff if you will all you Yankees and Canadians and other people who shovel snow. I’d like to see you survive 30 days of 110ºF+ in a row.
