LEDs come in a number of shapes and forms (including the organic LED and polymer LED), but the basic LED is a semiconductor. They are small, long-lasting, and power efficient. They are made of a semiconductor material in order to produce the desired color tones.
How LED works is not particularly complex from a scientific point of view, but it’s quite far removed from the purchase and usage of LED lighting. Lots of information is available if you’d like to dig deeper into the physics and chemistry behind semiconductors, but it should suffice to say that an LED is a diode—a device that allows electricity to pass through it in a single direction—that emits light. That light can range from infrared (non-visible) through the color spectrum, depending on the semiconductor material that is used. For example, a red LED might use aluminium gallium indium phosphide (AlInGaP) and a particular voltage drop (from one side of the diode to the other) to emit the desired color.
White light is the combination of all of the colors in the visible spectrum. Because of this it can result in a number of shades, and producing it is not as easy as just using a particular semiconductor material. There are a number of different methods for producing white light, some of which are more energy efficient than others, and some methods are patented by particular companies. Once you factor in this information and secondary facts, such as the blue LED light is cheaper to produce than white light, then you can start to understand why LED lighting is such a scientific enterprise.
It’s worth understanding that there are a few factors that make LEDs an excellent light source. One major strength is lifespan; not only can most LEDs last for tens of thousands of hours, but LEDs don’t immediately die. Rather, LEDs experience lumen depreciation, which is a fancy way of saying they lose brightness over time. A well made, properly cooled LED might only lose 5% of its brightness over 20,000 hours of operation. However, this drop off will depend on the cooling and power consumption—LEDs can get more power pushed through them to produce more light (think of this as overclocking it), but it will shorten the life. Heat also has a major role in LED lifespan. LEDs that run in high temperature settings will not last as long as they otherwise would. This is why cooling is so important and many LED bulbs have large, metal heat sinks.
It’s interesting to note that while LED bulbs get less bright over time, this lumen depreciation happens in all lighting. In incandescent bulbs, tungsten loss over time means a decrease of about 10%–15% over the 1,000-hour life of the bulb. In CFLs, there can be as much as a 20% loss over a bulb’s 10,000-hour lifetime.
Other strengths of the LED include quick start up times, the ability to cycle on and off frequently without damaging the light producing parts, and ruggedness (these are solid-state gadgets, after all).
And the weaknesses? Currently, LEDs are expensive (though that’s changing quickly), they are greatly affected by their operating temperature, and, as stated before, they can produce low quality (that is to say, low CRI) or overly blueish light if measures are not taken to correct for this. Finally, LEDs are directional, so manufacturers must ensure that the lamp’s housing can direct the light if necessary; while consumer bulbs are often omni-directional, other types, like PAR and MR bulb shapes, are highly directional.
Interestingly, the companies that sell LED bulbs aren’t always the companies that manufacture the actual LEDs. LEDs are generally made by companies like CREE, Nichia, Osram Opto Semiconductors, and Philips Lumileds. Manufacturing is important because it can affect pricing, which is the single most important factor in consumer lighting. Companies like Switch Lighting are manufacturer-agnostic, so they can buy LEDs based on who offers the best deal at a given time and whose product fits their specifications and quality requirements.
Despite their extended lives, all LEDs eventually die out. As stated before, LEDs don’t stop suddenly, they lose brightness over time. So then, you might be wondering, how companies evaluate their lifespan. LED manufacturers and the US Department of Energy typically use the 70% brightness mark (L70) as the point where the “useful life” of a bulb is spent. The amount of time it takes to get to this point will vary based on the conditions in which a bulb is used, how well it’s cooled, and how the parts, particularly the electronics, hold up. After all, just because the LEDs can last a long time doesn’t mean that the power supply and other electronics can last that long. This is one reason why lamp design is much more complex than simply providing power to a few tiny circuits.
Example 3-1. DIY LEDs
One of the best ways to learn about LEDs is to put down the books and try them out for yourself. While there is all sorts of interesting science involved and bulbs are quite complex, the basics of LEDs are right out of a high school science class. There are pre-made kits available online that will give you all the parts and instructions you need in order to start tinkering with LEDs, and to understand them at a basic level.
The most basic LED kit you can build is an LED throwie. It’s nothing more than an LED and a power source—in this case, a battery (usually a CR2025 or CR2032). The best about this project is that you only need to know two facts: the sides of the battery and the sides of the LED. Each of the components has just two sides. The LED will have two wires coming out of it: the short one is the cathode (the negative side) and the long one is the anode (the positive). The same is true with the battery, where the flat side is the positive and the smaller, inset side is the negative.
To construct an LED throwie you simply need to match the positives and negatives, creating a circuit. (Usually there is a magnet involved so that it will stick to metal objects, like a refrigerator.) Pretty simple, right?
If you’re at all familiar with the basics of electronics—maybe you’ve put together an kit or two—then you might know that a simple LED circuit usually has a resistor in place. The resistor limits the amount of current that goes to the LED from the power source. By using the correct resistor, you’ll ensure the longest possible life for your LED and prevent any possible damage to it. Basically, what it comes down to in this case is that you could use a resistor, but you probably don’t have to. The LEDs will operate along a curve where more current means less lifetime, and since LEDs and batteries like these are cheap, they are easily replaceable.
If you want to stick with the DIY angle, and learn more about the circuitry, switches, and resistors try out a kit like those from Maker Shed, LittleBits, or Sparkle Labs. Maker Shed’s Mintronics: Survival Pack is a cheap way to get started: it includes a mini breadboard, some LEDs, resistors, and other components such as a 555 timer chip, which can blink LEDs.
If you want to take things to the next level, you could seek out the MinM. This little gadget combines a programmable LED with a bit of silicon. It’s smarter than the typical LED bulb, but it’s ripe for all sorts of experimentation with computer languages, wearable electronics, and soldering.