LEDs: Light Emitting Diodes

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Podcast Transcript

One of the most important inventions in human history was artificial lighting.

With the electric lightbulb, the night could be illuminated, allowing people to extend the productive hours in a day and to work in places that were otherwise difficult or impossible. 

While the incandescent bulb was a breakthrough, it wasn’t actually very efficient. It wouldn’t be until decades later that a radically more efficient way of producing artificial light would be developed.

Learn more about LEDs or light-emitting diodes and how they work on this episode of Everything Everywhere Daily.

Before I get into LEDs and how they work, I should first take a step back to address the history of artificial lighting and why there was a need for LEDs in the first place. 

In a previous episode, I covered the history of the incandescent light bulb, so I’m not going to belabor the point, but the incandescent light bulb was indeed a huge breakthrough. 

The phenomenon of incandescence has been known for thousands of years. Basically, when something gets hot, it will glow and throw off light. This effect can be seen with a metal rod that has been put into a fire or even with hot wood embers. 

Incandescence works and is simple to understand, so the development of a working, practical light bulb was more a matter of finding the right material to heat up and creating the right environment for it to incandece in. 

Eventually, filaments that allowed for a bright, glowing white light were discovered. They were encased in a glass container that either held a vacuum or some inert gas that prevented the filament from burning up. 

For over a century, these types of incandescent light bulbs were the overwhelming dominant form of artificial light.  This is the type of light bulb that most of you probably grew up with and are most familiar with.

However, these bulbs had a problem. They were extremely inefficient. 

Most of the electricity that went into an incandescent light bulb didn’t produce light, it produced heat and other non-visible wavelengths of electromagnetic radiation. 

Some of you might remember a toy called an Easy Bake Oven. The Easy Bake Oven was a children’s toy that could actually cook small cakes and treats. 

The Easy Bake Oven used incandescent light bulbs as its heat source, which should give you an idea of how much excess heat was given off. 

Only about 5 to 10 percent of the energy used by an incandescent bulb is actually converted into useful, visible light. 

Lest you think that this heat might be a good way to heat a house, I assure you it is not. There are far more efficient ways to heat a house and in many parts of the world, the last thing you want to do is make a house hotter. 

In addition to being inefficient, the nature of incandescent light bulbs gave them a finite lifespan. Once oxygen got into the bulb, they would burn out, literally burning. 

Many alternatives were developed to solve the inefficiency problem with incandescent lightbulbs. Most of these involved sending an electrical current through a gas such as mercury vapor. These types of bulbs, like fluorescent bulbs, are more efficient but still waste 65% to 75% of their energy as heat. 

The ideal light source would be one that simply produced visible light and little else. Something that could convert most of the electricity consumed as light. 

This is where LED’s come into the picture. 

LED stands for Light Emitting Diode. They should not be confused with the similar-sounding LCD, which stands for Liquid Crystal Display. In addition to the similar-sounding names, LEDs are often used in conjunction with LCDs.

A diode is a small electronic component that acts like a one-way valve for electric current. It’s made from a type of material called a semiconductor which has been treated to create two different regions within the diode: one that has extra electrons (called the N-type) and another that has spaces for electrons (called the P-type).

When electrons cross the regions of a diode, they can exhibit what is known as electroluminescence. In other words, the semiconductor will emit photons of light.

Electroluminescence was discovered in 1907 by radio engineer H. J. Round of Marconi Labs, who was experimenting with a crystal of silicon carbide.

However, the first true light-emitting diode was developed by the Russian inventor Oleg Losev in 1927. 

Losev’s discovery was published widely and known in many circles, but it was mostly considered to be a curiosity with no known practical purpose. 

There were experiments conducted on the diodes and electroluminescence for the next several decades

In 1961, James R. Biard and Gary Pittman of Texas Instruments developed an LED that emitted light in the near-infrared part of the spectrum with a 900nm wavelength.  

The first LEDs that created visible light were all developed independently by three different research teams in late 1961 and 1962. The teams were from the Philips Central Laboratory in Germany, Bell Labs in the United States, and the Services Electronics Laboratories. 

All three teams were working on totally different projects and arrived at somewhat similar solutions.  Many of the different approaches used different types of semiconductors made out of different materials. 

Here, I should note a problem with these early LEDs. The first problem is that they were all single wavelengths of light in the longer wavelength part of the spectrum. All of these first LEDs were some form of the color red.

It was simply easier to create lower energy photons from this part of the spectru. They emitted visible light, but it was far from white light that could replace general incandescent lighting. 

The second problem was that the light that was produced was very dim. 

That being said, there were uses for these early red LEDs. In 1968, the first mass-produced red LED indicator lights were commercially available. They were made out of Gallium arsenide phosphide by the Monsanto Corporation.

You’ve probably seen any number of electronic devices that had a simple red light to indicate if something was on or off. That was most probably an LED. 

They actually were the perfect solution for such simple lights. They used very little power, were cheap to make, and they almost never failed.

In 1969, Hewlett Packard introduced the HP5082-7000. It was a series of LED lights connected to an integrated circuit and could display simple letters or numbers. It was the world’s first digital display.

In the 1970s, the price of LEDs dropped to under five cents for simple red ones. Further advances in semiconductors resulted in the creation of yellow and green LEDs during the period. 

However, developing LEDs that produced shorter wavelengths of light towards the blue end of the spectrum proved to be difficult. There were weak blue-violet LEDs produced as early as 1972, but nothing bright and truly blue.

The big breakthrough came in 1993 when Shuji Nakamura of the Nichia Corporation in Japan demonstrated a bright blue LED using Gallium Nitride as the basis for the diode. Simultaneously, Isamu Akasaki and Hiroshi Amano of Nagoya University were also developed

The development of a blue LED was actually a huge breakthrough. Nakamura, Akasaki, and Amano were awarded the 2014 Nobel Prize in Physics for their discovery. 

Why was a blue LED such a big deal? Because blue is necessary to create white light LEDs. White isn’t a color, it’s a mix of colors. In particular, you can get it by mixing the primary colors of red, green, and blue. No blue light, no white light. 

That being said, just taking three different colors of LEDs didn’t produce a very good white light.  The better white LEDs were just blue or ultraviolet LEDs with a phosphor coating which created white light. 

The first white LED was released by the Nichia Corporation in 1995. 

These first white LEDs that were commercially released in the late 90s were expensive, not very efficient, and had a poor quality of light. 

However, throughout the first two decades of the 21st century, LED technology has continued to improve.

The brightness of LED light has improved dramatically, the color of white LED bulbs has improved, and the cost has come down. 

The initial argument in favor of LED bulbs was that even though they cost more, the reduced electrical consumption coupled with their longer lifespan made them a better deal than cheap incandescent bulbs. 

Even though that was true, many people balked at paying such a large amount for just a light bulb. 

However, within the last five years, prices have dropped to such a point that even the purchase of an LED bulb is a simple decision for most people. In my home, literally every lightbulb is an LED bulb today.  About 5 years ago, I made the switch and started to replace my incandescent bulbs with LED bulbs whenever they burned out.

A cursory check over on Amazon.com showed that the cost of white LED bulbs is now about the same as traditional incandescent bulbs. 

In fact, the only reason why LED bulbs are shaped like bulbs is because that is how incandescent blubs were shaped, and LED bulbs needed to fit into the older sockets. 

LED bulbs have a much wider range of shapes and form factors than traditional lighting. LEDs can come in strips, tubes to replace fluorescent lights or even flat panels. 

Not only can LED lights come in a variety of shapes, but it is entirely possible to have bulbs that can display a wide variety of colors. 

The efficiency of LED lights is remarkable. One of the measures of efficiency is the amount of lumens of light created per watt of power. A oil lamp produces 0.1 lm/W, an incandescent light bul produces 16 lm/W, a fluorescent bulb creates 69 lm/W, and a modern LED bulb creates 300 lm/W. 

The creation of efficient white LED lighting to replace incandescent lighting is not the end of the LED story. Not by a long shot. 

One of the next big uses for LEDs is what’s called MicroLED displays. 

Over the last several decades, enormous advances have been made in display technologies. In fact, it is probably worth an episode of its own at some point in the future. 

There have been plasma displays, LCD displays, OLED displays, and others. 

MicroLED displays have just begun hitting the market in the last few years. They consist of arrays of microscopic LEDs, 1/100th the size of a regular LED, that make up every pixel of the display. 

MicroLEDs have big advantages over other display technologies. For starters, they use significantly less power. That means less heat and less electricity to run a display, which is extremely important if the display is powered by a battery.

They are also thinner, which means they can take up less space and are lighter. 

However, perhaps more importantly, they have the potential for much better picture quality. They are much brighter, have more contracts, and have deeper blacks than LCD or OLED televisions. 

If all of that isn’t enough, this can be done on an otherwise transparent screen. Samsung Corporation just demonstrated a transparent MicroLED display at the 2024 Consumer Electronics Show in Las Vegas, just days before recording this episode. 

MicroLED displays are still new and are not yet widely available, but they should be one of the biggest technologies of the next few years. The barrier to wider adoption right now seems to be quality control in the manufacturing process. 

As with most technologies, the first MicroLED televisions will probably be incredibly expensive, and prices should fall rapidly afterward. 

It has taken a while, but the LED revolution is just getting started. The adoption of LED lighting is increasing at a rapid rate now that the price of bulbs has dropped, and MicroLED displays might soon become the dominant digital display technology. 

There might be a time when incandescent light bulbs and LCD displays are thought of in the same way as vinyl records and rotary phones.