In the first two parts, I gave a description of light sources and power distribution. Now I will give a little more of a description on the newest form of lighting, LEDs, and the technical hurdles that we'll need to mount to increase their market penetration and decrease their costs.
Light Emitting Diodes turn DC current into light. When first invented, they were limited to red, and then in time green, and amber colored light. Very poor in terms of lumens per Watt, they spent most of their first 35 years as either instrumentation, or a way to display information. As their efficiency improved, and their colors were broadened to blue and then finally white, their ability to produce light that did not change color with respect to intensity made them almost unique in terms of lighting technology. But they still have drawbacks which continue today, in terms of their being a part of mainstream lighting.
Why would you want to use LEDs?
Light output is measured in lumens . The efficiency of a lighting source can be measured as lumens/Watt )"lm/W", and the efficiency of a 100W incandescent bulb is about 17 lm/W. The bigger the bulb, the more efficient, but since most people don't use 1000 W bulbs (I do, but that's for testing switches) they pay a huge penalty. In fact a 40 W bulb is generally about 12.5 lm/W.
Some of the LED's I'm describing claim to have an efficiency of 160lm/W, which would permit you to (in a lossless system) use about 10% as much energy to achieve the same light!
- LEDs are semiconductors. So their "Current vs. Voltage" curve isn't simple like a light bulb, or a resistor- in order to get even the most microscopic amount of light out of them, you need to go beyond their initial operating voltage. For most LEDs, this is in the low 2 volt range, but some require as much as 4 volts before they turn ON. And once they are on, it isn't a simple equation, such as twice the voltage giving you twice the current and four times the output. Their current goes up disproportionately with respect to voltage. To put is simply, they operate on a very small range of voltages.
- Putting multiple LEDs in parallel, that is connecting them together where both leads are tied to each other, causes imbalanced light output. You will never get the same amount out of each, because one will always give off slightly more light than the other. In some cases, as when the batteries are dying on your LED flashlight, one or more "bulbs" might die out on their own, just because the voltage is too low for them "fire".
- So if you try to use them on household line current, you get a few little problems. First they'll burn to a crisp as the high voltage turns them from semiconductor to smoking heaps of melting plastic, possibly scattered all around the room. Second, they'll only conduct electricity half of the time. (That's not what the "semi" in semiconductor means, but in some ways it is an adequate description. They will only conduct in one direction, as long as their threshold voltage is met.) Now we can put two LEDs in series with each other, so the current flowing through one flows through both, and the voltage needed to make them work is twice as much as the earlier voltage. Put 50 LEDs in series (making sure they are all lined up in the same direction, and that they all work- like the old Xmas lights, one dead one prevents them all from working!) and you would be able to plug it into the wall socket, and see a flickering light.
Now there are ways to make them work. Remember in my earlier diary I discussed how you can turn AC voltages into DC; to recap, this is called rectification. The best way to do it is to take 4 diodes, arrange them in what is called a bridge and that will give you a choppy sine wave, with two positive half cycles, instead of one positive, one negative. Now the LEDs will turn ON 120 times a second, instead of only turning on 60 times a second, for 1/2 the time. But this is still not what you want- we still have to convert the ~173 Volts to a voltage low enough to keep the LEDs from melting. And we'd like some way to turn that sine wave into something easier on the eyes, a flat line.
To the rectifier we add a voltage regulator. This is now a ubiquitous device, inside of almost every device known to mankind. They come in several different electronic shapes and sizes, not to mention physical ones! Obviously, we want it to be small, and we want it to work for a very long time. And we also want it to be cheap- we're all unreasonable people here! I'll skip all of the variations and instead stick to the most popular and smallest, a switching voltage regulator.
This consists of a few small high voltage capacitors, an inductor, and a chip, along with a smattering of resistors. Capacitors store electrical charge, which is a good thing it you want to turn your sinusoid into a straight line. The inductor stores magnetic energy, and it doesn't like to have any changes in current. So we turn the current which passes through that inductor on and off a few tens of thousands of times a second, and have the resulting current try to keep the voltage on that capacitor the same, no matter how much we draw out of it.
I can see this being very confusing, so I'll try to make an analogy. The chip and the inductor act like a spigot and a hose. The capacitor is like a bucket, with a hole in it. Our load which in this case is the LED lamp, takes the power coming out of the hole in the bucket. The chip and the inductor try to make sure that the level of the bucket is the same at all times, to keep the flow going through the LED to be roughly the same.
The bigger the LED, the bigger the flow. Now if we want to build one big enough to replace a 50 watt bulb, you will need about 6 or 7 watts of LED light, which requires a power supply that can at least handle that much power. As of now, that's going to be bigger than 4 or 5 quarters stacked together. And you will need heat sinks to draw the heat out of the regulator (not to mention the LED, they aren't 100% efficient, and trying to generate that much light will also generate a lot of waste heat.)
So how do you do this, while permitting the LED light bulb to work in existing low-profile sockets and lamp holders?
I say, we don't.
Instead of using the standard light switch, the kind you buy at Lowes or Home Depot for $0.36 we design a new light switch. One that has the rectifier, voltage regulator, and heat sink built IN TO THE SWITCH. And since we want this fancy new LED to be dimmable as well, instead of a simple "ON/OFF" switch we'll use a rotary dimmer, or a sliding dimmer.
No more $0.36 light switch... I haven't done the pricing, but assuming that what I'm using in our 5 Watt devices doesn't go up too dramatically, it should cost about $6 to make it work for 20 Watts in serious quantities. Maybe more if we want to use a really good dimmer, with no dead spots and a good feel. So if it costs about $6 in parts to make in China, it would cost about $15 to $50 at the DIY store, depending upon how many people are willing to spend that much.
Now to get that much light you'll need an expensive LED, not a cheap little $0.05 job, and not even 100 of them. You'll need a killer, like the Cree XR-E (in fact, you'll need a few of them) for about $6 and change in high volume. Or you can use the Lamina NT-42D0-0426 (again, you'll need a few, but fewer than the Cree) and you'll need a radically different bulb architecture, more like a PAR parabolic reflective lamp than a round globe, and that too will require more money.
Hey, luxury and doing what's right for the planet ain't cheap. It will take you around $100 to replace that $1 light bulb. But it will last you for 20 years at least, so its $100 to replace $20 or more dollars in bulbs, plus for each year you'll save (assuming the bulb being on 4 hours a day) more than $10 a year in electrical bills.
Assuming $0.10/KWhour at 1460 hours a year, 100W bulb uses 146 KWhours per year, $14.60 per year, per bulb.
LED bulb and power supply will use about 20KWhours per year, maybe a little less, maybe a little more. That's $2. So that will save you about $13/year, add in the cost of the new bulb to about $14/year. Time to return on investment, about 7 years.
(Note: I'm currently paying about $0.18 KWH in the suburbs of NYC.)
In time, the costs will get cheaper, the return time smaller. But this is a start; we are on our way!