Light Thoughts

So I mentioned in my last post that there are two main reasons LED are such a big change from way we have previously generated light for ourselves. I discussed the electric versus electronic issue. Now I want to introduce the second issue: directionality.

All of our previous methods of generating light have been omnidirectional. That means that the light is radiated nearly all directions more or less equally. If you picture a candle, the light shines above and below and all around it fairly evenly. Some light is blocked below the candle, but that’s actually a shadow. The flame is still shining light down on the top of the candle.

That means that we can take as single candle, stick it in a room, and illuminate the entire space. It may not be very bright, but the light goes everywhere. The same thing can is true for light bulbs. The design of a traditional incandescent light bulb is pretty much the same as candle. There is a filament providing the light, just like a flame, and there is a base for holding the filament in place, just like the candle. We have developed various shapes for light bulb since then, but the only real difference is if the bulb has sockets on two ends so the shadow is on two ends instead of just one.

All the different sources still have the same distribution property. Incandescent, halogen, fluorescent, compact fluorescent, mercury vapor, sodium discharge, metal halide… They all send the light in all directions. Often, we don’t want the light to go in all directions, we want to be able to control it. So we have developed reflectors and refractors to help send the light the ways we want it to go and stop if from going where we don’t want it go. Just for clarification: reflectors are things like mirrors that bounce the light back either toward where it came from or in another direction we intend; refractors are things like lenses that let the light pass through them to the other side, but while passing through the light changes direction.

Going back to our candle in the room example, if we stick the candle on the wall so it stays out of the way, there is a bunch of light shining on the wall where it isn’t very useful to us. So, we stick a mirror on the wall behind the candle and (most) of the light that would have landed on the wall is now bounced back into the room where we want it. If we want to get even more useful light out of it, we can use a curved mirror instead of a flat one so that we can start to bend the edges around the flame to catch more of the light that would have gone onto the wall further from the candle and use that too.  Finally, we can stick that entire thing into a lantern and use a lens on the side toward the middle of the room to catch stray light and refocus it across the room. We have created a lighting fixture, and we have been using the basics of reflectors and refractors to control omnidirectional sources for thousands of years. We’re pretty good at it.

Now, we can take those omnidirectional sources and make them directional. PAR lamps and MR-16 lamps that you buy at the hardware store are examples of lamps that have the reflectors built onto the source. The filament inside is still omnidirectional, but it is built into a solid unit that does some of the work of the fixture. That’s why you often see light coming out the back of such sources either through gaps or through what appears to be opaque surfaces when the lamp is off.

The big change with LED sources is that they are truely directional. The diode is made up of layers and the light is only emitted out of one side. If you stick an LED in the middle of the room you don’t get light everywhere. It only lights the part of the room that the LED is “facing.” The other side of the room remains dark.

It may seem  like a minor point, but it really is important. Think of lighting up a space a building an object. The old way was to start with everything, both good and bad, then take away the bad parts. The LED way is to start with nothing and just starting adding things. The question becomes, how much do you add? With the old way, once you take away the bad parts which is pretty much the light going where we don’t want it, whatever is left over is useful. With the LED way, someone has to decide whether or not to keep adding.

So far, much of the LED lighting development has been driven by the need to reduce energy consumption. That means that LED sources have been designed by people who want to stop adding as quickly as possible. The problem is that people have lighting needs that are established without regard to the source or energy consumption, but by whether or not they can see well enough for whatever is it that they are doing.

Return to the example of a light bulb in a room. If we want to illuminate the room with LED sources, we have to add LEDs pointing in all directions. To illustrate, let’s imagine we take the guts out of a light bulb and glue LEDs onto the outside. How many do we have to add? One every square inch? One every square half-inch? Do we have the cover the surface completely? Then, we have to address the point of the previous discussion of the LEDs being electronic but the power is electric. Can we fit all the electronic components and drivers inside that light bulb?

In summary, the directionality of LED modules means we have to rethink and re-imagine how to develop a light source. It doesn’t mean that these problems can’t be solved, or aren’t being solved, it just means it is more difficult.

After two postings about LED lighting and working on more, I have decided I didn’t like the way the series was developing. It was too much cart before the horse. I want these posts to be useful for everyone and I felt the LED discussion was getting too technical without explaining why any of it mattered. Therefore, I am going to start over with a new introduction to LED lighting.

LED lighting is a game changer, but not in the way most people discuss it. It is not because of the efficiency or size or whatever, but because it is so fundamentally different from the way we have created light for ourselves. This may or may not be the future of lighting. It seems to be direction everyone is traveling at the moment, but that doesn’t mean we won’t find another alternative before we fully adopt, and adapt to, LED lighting.

There are two main reasons LED lighting is such a huge change. This post will focus of the first of the two, which is that LED lighting is an electronic, rather than electric, approach.

Imagine for a moment you are back in the early days of electric lighting. Up until this time, light was generated by burning a fuel at the point where you wanted the light to be. You might have a whale-oil lantern or a wax candle, but in any case the location of the light had to have both a supply of fuel to be consumed and a flame. At some point, your fuel would be used up and you would need more.

Then this new technology arrives that promises to change everything. By using an electric light you separate the fuel from the light source. Previously, if you knocked over an oil lamp you had to worry about a fire breaking out. Now, if you break an electric light bulb it just goes out. You no longer had an open flame at every light source. Now, each incandescing filament is surrounded by a glass envelope. Granted, there were still plenty of fires started by bad wiring or things touching a hot lamp, but it was a safer than having flames and combustible materials everywhere. You could wake up at night and press a switch to turn on the light instead of fumbling around in the dark for your taper.

The electricity became the new version of the fuel. How much electricity you got determined how much work was done by your motor or light bulb. You could plug in a light bulb and if you kept giving it more electricity it would get brighter and brighter until it broke. Electricity was “power,” and the power means getting work done.

All of our lighting advances since then have gone along the same lines: electricity means power. Various circuits have been designed to take advantage of that power in different ways, and different lamps take advantage of those circuits in different ways, but it is still essentially using electricity to power a light source, and creating that light is the work we want done.

LED lighting is different because electronics are different than electrics. Electronics use electricity as the power source, but they also use electricity as the information source. I’ll use digital electronics as the example since analog electronics are a confusing middle ground.

In a digital circuit the idea is to use the current as the information. Imagine you want a digital light switch. The entire device will need two circuits: one circuit to figure out if it is supposed to be off or on, and a second to actually power the light. The two circuits can’t be shared, because if they were the result would be something like: “if the light is on, turn the light on, and if the light is off, turn it off.” That wouldn’t actually do anything useful. Instead, we have one circuit which is “smart.” It knows that if the current flows in a particular direction at a particular power, it is supposed to be “on.” If the current doesn’t meet those requirements, it is “off.” If the control circuit is “on,” it tells the work circuit to flow, turning on the light.

The point here is that diodes, like an LED, were and are designed to function as a part of the control circuit, not the work circuit. To make LED lighting work we have to design a control circuit act as a work circuit. That’s the point of including the stuff about circuit boards and drivers in my previous posts. Power is supplied from the power company in the work circuit form, which then has to be converted to a control circuit form to let the LED function. However, the LED has to function as a work circuit, and the only way that can be accomplished is by proper fixture design. That’s why we can’t just stick a bunch of LED modules on a wall and expect an efficient and effective lighting system.

LED lighting is a complex subject. It is new, and it is a game-changer. I’ll endeavor to make this all comprehensible.

Part of the problem is that LEDs are an electronic component, not a traditional lighting source. I believe that is the root of nearly all the confusion. We’re trying to shoehorn components that are meant to build things like computers and radios into a lighting fixture. LED stands for “light emitting diode.” We’re trying to take advantage of the “light emitting” part, but the component is still a diode. The traditional function of a diode is to control the direction of an electrical current.

LED proponents have a variety of claims for the advantages of LED lighting. The most common claims are that LED have higher efficiency and long life than traditional lighting sources. These claims are technically true in a laboratory setting, but in the real-life application the picture is much more complex. Development is taking place, and someday the full potential of the LED light may be realized, but that hasn’t happened yet.

Over the next few posts I’ll address issues surrounding LED lighting in what I hope will be understandable bite-sized chunks. I’ll address energy efficiency and lifespan, but also get into other factors such as color and light directionality that affect the use of LED in lighting but get less popular coverage.

As an aside, an OLED is an LED where the emitting layer is an organic compound instead of an inorganic compound. They are a newer development and less efficient at present, but one of the exciting aspects of them is that they can be flexible. Developers are looking at them for flexible displays and luminous cloth.