Light emitting diodes, or LEDs, have been heavily featured in the entertainment industry news recently. There's the lawsuit between Color Kinetics and Supervision, of course, and a proliferation of new fixtures are appearing, particularly in Europe. Everyone is getting excited, but LEDs have been around as light sources for over 40 years. So, why are they suddenly attracting so much interest?
LAMPS THROUGH THE AGES
To answer that question, we need to briefly look at the history of LEDs. You might describe LEDs as the only fundamentally new lamp technology to enjoy commercial success in the last 100 years. Incandescent lamps have been around since the 1830s, with the defining commercial moment being Edison's Menlo Park patent1 of 1880. Arc lamps are even older, dating back to the early 1800s. You might have thought that fluorescent lamps are a modern invention, but this is not so; although they weren't commercialized until the 1950s, the fundamental principles behind their operation were known in the 1860s, when Becquerel demonstrated them in Paris. Sulfur lamps were new in the 1990s, but so far, they haven't yet been a commercial success.
LEDs made the transition from the laboratory to commercial products in the early 1960s. The first devices were infrared only (no visible light), but they quickly found commercial use in sensors and scientific instruments. Their history since then has been a step up in frequency, from the invisible infrared to the visible, with red appearing in the late 1960s, green and yellow in the mid 1970s, and blue in the 1990s. Most recently, they've left the visible spectrum at the other end, and ultra-violet (UV) LEDs are now available.
Those early red LEDs quickly became ubiquitous as indicators — every electronic device adopted them to replace incandescent lamps. LEDs were smaller, easier to control, more robust, and looked cool. They were a perfect component for the consumer electronics industry that was experiencing huge growth on the back of the recently invented transistor and the brand new integrated circuit.
That's where things stayed for a while. We got green, yellow, and blue indicators, as well as red, and they got steadily brighter. Today, those indicators are everywhere. It's projected that every traffic light will be LED-based by the end of 2005, and auto manufacturers are rapidly switching to their use in taillights. Don't forget LED video screens — it's getting hard to remember what Las Vegas looked like before LEDs!
INDICATION, NOT ILLUMINATION
All these applications, however, are for indicators where you look directly at the light source, not for illumination where the light source shines onto an object. To do that, you need a much brighter source.
At the same time LEDs were climbing the frequency spectrum, they were also increasing in brightness. We have all heard of “Moore's law,” which predicts that the number of transistors you can cram onto an integrated circuit will double every 2 years. LEDs have their own law, dubbed “Haitz's Law” after Dr. Roland Haitz who worked at HP/Agilent/Lumileds. From examining the historical data, he showed that LEDs had been doubling in brightness every 18 months since they were first commercialized and that there seemed every expectation that this trend would continue (Figure 1).
Improvements over the last five years have meant that we have seen niche illumination applications open up. LEDs are now bright enough for museum lighting, accent lighting, outdoor path lighting, and other low-demand requirements. Of course, the whole entertainment lighting industry is, by definition, a “niche” market, and we always love anything new — it's fundamental to our business. We have become early adopters of the technology. However, entertainment lighting is a tiny market compared to general lighting so, although our uses are exciting, it's not the real goal. We are just a spin-off application, I'm afraid.
BRIGHTNESS ISN'T EVERYTHING
We talked above about Haitz's law and brightness, but just as important as the light output of a device is its efficiency — it's no good getting the required light output if it takes more energy to do it. For commercial lighting, the targets are the incandescent and fluorescent lamps, the current workhorses of the lamp industry. If you can replace those with more efficient light sources, you can achieve true energy savings, something governments are rightly very enthusiastic about — so enthusiastic, in fact, that in 2002, the US passed legislation, the “Next Generation Lighting Initiative,” supporting research into these technologies. At that time, the Department of Energy, working with the OIDA (Optoelectronics Industry Development Association), established the goals in Figure 2.
So far, we are pretty much following this path (Figure 3). Commonly available LEDs have overtaken incandescent lamps for efficiency but only just. That means they are achieving about 20 to 30 lumens/Watt. To put that figure in perspective, an HID lamp (such as the familiar MSR or HMI) pushes the bar up to about 80 lumens/Watt, and some current fluorescent lamps top the list at 100 lumens/Watt.
If these goals are achieved, and the government thinks they will be, commercial and domestic incandescent lamps will see serious competition in three years, fluorescents in five years, and LEDs will dominate the world by 2020. You can see why lamp manufacturers are taking notice. The benefits are obvious, not just in energy savings but also in reduction of mercury pollution (every fluorescent lamp contains mercury), savings in maintenance costs, and extended lamp life.
SO, WHY GET EXCITED?
At last, we are coming close to answering the main question: why are we getting excited right now? Well, three years is a very short time in product development. It really means you should be thinking about it today, or you won't be ready in time. In fact, two or three years before commercial acceptance is just about the time when the early adopters start to show niche products, and guess who's an early adopter? The entertainment lighting industry — that's who.
Of course, all this is still a projection, not reality, and we shouldn't take any of the developments needed to achieve these goals for granted. New discoveries, new technologies, and new techniques are needed to compete with incandescent lamps, never mind fluorescents. The humble MR16 lamp for around $1 is really tough to beat.
Assuming that these high power, high efficiency LEDs can be produced, there are still many problems to be solved. Our old public enemy #1 has still to be addressed: heat. LEDs are very sensitive to overheating. Not only does heat significantly reduce life and reduce output, it also changes the color of the light emitted. LEDs need a much cooler environment than an HID or a theatrical incandescent lamp will tolerate. That means more work and resources must be invested in cooling system design.
GETTING THE SAME COLOR MORE THAN ONCE
To make it even more complicated, different color LEDs change output and color with both temperature and age but at different rates. Imagine the difficulty of designing a unit with red, green, and blue LEDs where you are trying to mix a specific color and make it match between fixtures. Firstly, the three colors age at different rates — the blue might drop in output almost twice as quickly as the red so that, at 10,000 hours, the blue LED could be giving only 50% of the output it gave when new. Then, they have different temperature dependency — they all shift toward longer wavelengths (i.e., get redder) as the temperature rises but, again, by different amounts. The combination is mind-bogglingly confusing. The LED manufacturers are working hard to reduce these effects, and the latest high-power devices are much more stable than previous generations, but these are still serious issues that require innovative solutions.
These are tough problems, but none of them is insurmountable given the ingenuity in this industry. I'm looking forward to seeing some of the off-the-wall solutions in development.
We don't want LEDs just because they are efficient, of course. We want them because they have the potential for a stunning color range with dramatic and instantaneous color strobes; we want them because they give a cool, heat-free beam; we want them because they look good; and, perhaps most importantly, we really, really want them because they are new, and we thrive on novelty.
Interesting to note that Edison's Patent (# 223,898) not only discloses the electric lamp but also the coiled filament still used today.
OIDA, NEMA, Department of Energy Roadmap update - October 2002.
After an early career as a lighting designer, Mike Wood has been responsible for the technological strategy, R&D, standards, and IP in many different companies within the entertainment industry. He is the current president of the Entertainment Services & Technology Association (ESTA). Mike can be contacted through his company, Mike Wood Consulting LLC, at firstname.lastname@example.org.
|LED 2002||LED 2007||LED 2012||LED 2020||Incandescent||Fluorescent|
|Input Power, W/lamp||1||2.7||6.7||7.5||75||40|
|Lumen Cost, $ / 1000 lm||200||20||<5||<2||0.4||1.5|
|Lamp Cost, $||5||4||<5||<3||0.5||5|
|Color Rendering Index (CRI)||75||80||>80||>80||95||75|
This shows the basic structure of a generic LED chip. Fully solid state in construction, there are no filaments, no moving parts, and no glass components. Although the LED is based on a series of layers of semiconductor material, it behaves mechanically as a solid block of a very robust material. As a result, breakages in transportation or during assembly into products can be virtually eliminated. With proper heat management and good supporting electrical design, this rugged device should be able to achieve significantly longer life than other lamp technologies.
- Chris Bohler, PhD, Director of New Product Development, GELcore