Light Emitting Diodes... LEDs - we interact with them on a daily basis and can be found in or on nearly every piece of electronics or electronic devices from SBCs (Single Board Computers) to street lighting and everything in between. The technology isn’t exactly new, in fact, they’ve been around since their modern inception in 1927 by Russian inventor Oleg Losev with no practical purpose in mind. Only decades later would they find function in communications, indicators, illuminators, displays, and machine vision systems among a host of others.
These tiny light-emitting diodes have come a long way regarding technology and come in many different kinds, types, and shapes, all of which are manufactured in different ways and for a myriad of applications. Advancements in LED technology have led to more efficient and brighter illumination, longer service life (25,000 hours or more) and lowered power consumption over their incandescent predecessors. With all these different parameters, it may be daunting or even overwhelming when deciding which type is right for a particular application. As such, this article will attempt to provide a brief overview of all things LED- from manufacturing, types and which are best for certain applications.
Types and kinds of LEDs-
Various types and sizes of LEDs. (Image credit Afrank99 via Wikimedia)
There are many types of LEDs current available on the market, which come in many different shapes and sizes. However they can be broken down into three separate categories- miniature, high-power and AC driven, two of which have subsequent sub-categories
1: Miniature- These are the most common types that can be found and are usually single-die LEDs and range in size from 2mm to 8mm. Although there are RGB versions of in this category, they’re usually available in a single color format and are widely used for indicators on devices such as calculators, cell phones and remote controls. These types are also common on circuit boards for use as status indicators such as power flow and diagnostic applications. There are three subcategories for this type-
A: They are often low-current and rated at 2mA at around 2V and therefore don’t require a separate heat sink to dissipate heat.
B: The Standard version miniature LEDs are usually rated at 20mA and range in voltage depending on the color- 1.9/2.1V (red, orange, yellow and green), 3/3.4V (pure green and blue) and 2.9/4.2V (pink, violet, purple and white.
C: The Ultra-High output versions are rated at 20mA with a voltage range of 2 to 5V and are outfitted with a suitable series resistor for a direct connection to a power supply (5-12V)
2: High-Power- Advanced diode technology has given rise to this version as they offer higher illumination output over the Standard series. These can be driven at currents ranging from hundreds of mA to an ampere, with some emitting over a thousand lumens. As a result, these must be connected to a heat sink or their bright life would be cut short (think seconds). These LEDs are commonly found in vehicle headlights, flashlights and industrial applications due to their high-lumen output.
3: AC Driven- These can operate on AC power without the need for a DC converter, meaning part of the LED is lit, and part of it is dark during each half-cycle, which is reversed for the other half. The benefits of this type allow it to function with a simple controlling circuit with low-power dissipation.
4: Surface Mounted- SMDs are a special type of LED that feature wire leads but instead, have a pair of tiny metallic contacts that can be soldered directly onto circuit boards. These types are typically smaller than traditional LEDs, making them perfect for space-limited boards and other electronics. SMDs are also highly robust as well, able to handle shock and vibration with negligible impact on performance. These types of LEDs are often found in mobile devices, RF and low-power applications.
Semiconductor materials, chemical elements, and impurities are required to manufacture LEDs. (Image credit Flickr)
While there are many different LEDs regarding size, shape, output, and color, they are all manufactured nearly the same way with differences lying in the materials used to create them. That being said, they all begin life in the form of raw materials, such as gallium, arsenic and/or phosphor, which are all mixed together inside of an enclosed chamber and forced into a solution. The solution is heated and usually covered with a liquid layer of boron oxide to keep it from escaping and mixing with the pressurized gas in the chamber.
A rod is then lowered into the solution and slowly removed, after which the solution cools and crystallizes as it’s removed from the chamber forming a crystal ingot, which is then sliced into thin (approximately 10 mils thick or larger) wafers. Impurities (also known as doping, usually with zinc, silicon, germanium, nitrogen, etc.,) are introduced (grown as additional wafer layers) during this process to create density for electrons to easily flow back and forth and make the LED function correctly. The semiconductor substrate and the impurities used determine the color of the LED being produced.
To complete the manufacturing process, wires are then introduced to the wafer, usually in the form of gold or silver as they bond to the substrate exceedingly well, making them ready for soldering into a circuit. The LEDs are then usually coated in a transparent polymer that varies depending on the optical properties required- diffusive, transparent, tinted can all be applied depending on the LED design and application needs. Of course, this is the simple explanation of how an LED is born but for those looking for a complete in-depth production process, complete with various analysis should look the Department of Energy’s Lifecycle Assessment of LED Products report.
Choosing the best LED for applications-
Choosing the right LEDs depends on the application. (Image credit Kevin Savetz via Wikimedia)
Choosing the right LEDs for any number of projects can be a daunting endeavor and essentially boils down to the application they are being used for. Does it need to be mounted to a circuit board, does that board have specific heat or voltage restrictions? What about power requirements, do you need constant current or constant voltage, then you will need a driver to provide variable voltage. Does the project require a single LED or a chain, how about color and lumen output?
Are the LEDs for industrial use, signage or displays? Perhaps your project is centered on communication and needs an IR bulb? These are just a few of the factors that will help you decide which LED is right for the application as there is no easy answer, outline or PDF that can guide you to the ideal solution from start to finish. It begins with your project goal, transitions to the requirements needed and then gives you a direction on what best to use.
Online help from a myriad of different companies can also help determine which is best for the application. Cree, Osram Opto Semiconductors, Everlight, and Samsung are a few leading manufacturers that have a wealth of repositories to help guide you in your search. They even offer data-rich information on the myriad of products they offer, further helping you to refine your choices. With that being said, it all boils down to your requirements and expected results, which is the first step in finding the right bulb for you.
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