What you should know about HBLEDs – and nobody will tell you – Part 1

Technology News | June 18, 2014

By eeNews Europe

Part 1: A Brief History of Light

Introduction

Over the past 7-8 years the introduction of useful white-light High Brightness Light Emitting Diodes (HBLEDs) has captured the fancy of not only the engineering community but also the financial community.

Press releases have described how these new devices will render obsolete the 140-year-old invention of Thomas Edison and that ”the future is now!.” In fact, there is a recently published book, by Jane Brox, on the history of artificial light. The book was summarized in an 8/1/10 Boston Globe article as “The Incandescent Lamp: An Obituary”.

The Internet today is packed with hundreds of companies offering HBLED products of one kind or another. Furthermore, many component makers and design consultants – for LEDs, lenses, power supplies, heat sinks, control circuits – have an agenda – nothing wrong with that – but they are unlikely to be an expert in all the companion elements and they certainly are not going to tell you things which might be limitations of their own products.

There is evidence that, because LED technology has evolved so rapidly, there are actually very few people who really understand all the technical interactions beyond a superficial level. Unfortunately, customers are also confused, whipsawed and otherwise befuddled by the various claims being made by the many firms now hoping to cash in on this increasingly evident technology.

There is extraordinary potential here for energy savings, new functionality, longer product life and greater reliability. However, in order to separate “the steak from the sizzle,” we need to look at some of the lesser-known physical principles and manufacturing technologies that make HBLED lighting possible and at some of the irksome issues not talked about.

Hopefully, the following commentary will put a few developments in perspective and provide an understanding for some of the aspects of the market that are not usually evident.

The Lighting Market: A Two-Part Equation

In a discussion of the lighting market and the potential for HBLEDs, it is important to make some fundamental distinctions. They will not apply to all market categories but can safely apply to over 95% of the areas of opportunity. First of all, we can divide the market into its two principle areas: Illumination and Indication. Even the hearty souls involved with the alpha-tests of fire as a light source made the made this distinction.

Illumination is that kind of light which helps us view our surroundings or perform tasks better. Indication is that kind of light which informs or alerts us relative to the status of something or otherwise provides us with information. They are as different as night and day and it is critically important to appreciate the difference.

Applications involving illumination fall into three subcategories: a) general area lighting, b) directed lighting and c) backlighting. The applications where light is used for indication include a) panel indicators and b) messaging.

Table 1 provides a way of looking at the HBLED market in a little more detail. The items marked with an asterisk (*) show where HBLEDs have enjoyed their principal successes. It’s interesting to note that until 2011 there was not much change in this makeup over the last 7-8 years but there has been accelerated movement since.

TABLE 1: The Lighting Market Broken Down by Application

General Lighting
Incandescent room lighting
Ceiling fluorescents for offices, factories, stores
HID lamps for factories, warehouses, streetlights, ballparks
Portable Lanterns
High Bay Lighting for warehouses/”big box” stores/factories

Directed Lighting
Track lights
Floodlights
Headlights
*Flashlights
Downlights
Studio Lighting

Backlighting
*Commercial signs
*Cell phone, camera, automotive and other large LCD displays

Indication
Panel Indicators
*Equipment status
*Operator Guidance

High Awareness Messaging
*Highway and Railway Traffic Lights
*Brake Lights
*Hotel/Theater Marquee signs
*Commercial & Highway Message signs
*Giant Color Graphic Displays,including TV’s
*Warning/Safety Notification

Each of these subcategories has its own unique performance, cost, and reliability expectations. It’s also worth noting that in some cases there are additional physiological and psychological nuances that have to be considered in the marketing of such items.

Up to now, the lighting industry has been represented by thousands of different types of incandescent lamps, developed over a hundred years in response to evolving market needs. Those needs are extraordinarily diverse and one might suggest that the chances for replacement of all these by a single super-efficient LED technology would be slim to none. Similarly, there have been hundreds of fluorescent lamp types developed over the last 50 years.

It does mean, however, that an increased appreciation of all the nuances of these categories can lead to more effective leveraging of HBLED technology by companies with new and exciting value-add technologies which are market and application driven.

In this pioneering market, the HBLED makers are saying: “Here’s my fantastic new LED…. please find a way to use it!.., and please give us feedback on how you got around the various limitations… because we haven’t figured that out ourselves yet!” As this paper is being written there is not yet a single, truly high volume application for LEDS in general lighting over 10 watts. Nevertheless, as LED prices have dropped significantly since 2013, LED bulbs and luminaires are increasingly finding their way into mainstream applications for legitimate reasons.. and that trend seems likely to accelerate.

Indeed, many lamp and fixture makers are collaborating with this or that government entity, on a subsidy basis, with a commercial entity to install LED lighting on a trial, promotional or utility rebate basis… so,until 2013 very few installations to date have happened on the merits alone…. but that has changed.

One must be careful in extrapolating the early pace of success of HBLEDs in some a very few markets toward inevitable success in most all other possible markets. Success in traffic lights (the most publicized HBLED success story) has been no surprise because of the dramatically better lamp longevity (eliminating the very high cost of highway department bulb replacement labor costs) and elimination of need for the red, green and yellow colored lenses which curtail light efficiency.

With traffic lights, it simply was obvious that conversion to LEDs was a foregone conclusions – virtually all plusses and no minuses. For supermarkets, malls, warehouses, streetlights, museums, sports and entertainment complexes etc, there still are many technical issues, beyond just lumens per watt that the industry is still learning to appreciate. Addressing these nuances will “separate the men from the boys”

Traffic lights were a real functionality and “return on investment” success story. High end automotive lighting for brakes or headlights has also been getting attention but that has been more style driven and does not represent a mainstream application

The contrast between Indication and Illumination is striking. The fact that there are some products being offered in every single category including Illumination simply confirms that there are some “early adopter” buyers for almost any high tech product, whether it’s a Segway vehicle (12 years ago), video conferencing (20 years ago), or the first generation Kindle-type readers (10 years ago).. At this stage of a developing market, it’s sometimes not clear whether an innovation is simply a solution in search of a problem or really the next big thing, but it is important to appreciate that it could be either.

A good example of the time lag between a technology’s introduction and its finding a home in the mainstream market is the energy-saving compact fluorescent lamp (CFL). Some major lighting companies, such as Westinghouse and Philips were making and promoting their first CFLs in 1983 but that did not mean either were ready for prime time. In fact, it took 15 years, for CFLs to get market traction. Gas/electric hybrid vehicles are also following a similar long adoption curve. Despite this caveat, it’s also useful to note that the mistakes or off-the -mark assumptions of the earliest product innovators are often a textbook for the next individuals or companies to ”get it right” from a pragmatic business standpoint.

Understanding the Popular Light Sources

Before we look at HBLEDs it’s probably a good idea to understand the competition. We’ll begin with a quick overview of two well-established technologies which cover over most of our current lighting needs: incandescent and gaseous discharge, before we take a look at newer solid-state solutions.

Incandescent

Incandescent lamps are the types we’re most familiar with. Whether they’re regular bulbs or their higher-performance halogenated brethren, all such lamps operate on the basic principle of heating a wire, within an atmosphere of selected gases such as argon and krypton, until that wire is white hot. In a very predictable time period, the material of the filament “boils off’ just like boiling water in a pot. Halogen lamps are essentially regular incandescent lamps but contain additional specialized gases under greater pressure, to allow the filament to burn hotter/brighter, without boiling off as fast. The principle is exactly the same as in grandma’s pressure cooker.

The filament gets thinner and then and finally breaks, at which time it acts like a fuse opening up. You often see the “blowing “ of this fuse, at the end of bulb life, as a sudden, momentary brightening of the lamp. There is always a momentary surge of current at turn on. That turn-on surge is always harmless except at that one time when the bulb filament is as thin as it can get. That one last surge blows it like a fuse and typically does a brilliant, fraction-of-a-second, “flameout”’

The basic design of these lamps has not changed much over the last 75 years, and neither has one of the primary design trade-offs which balances lamp temperature (how fast it boils off) against output color (whiteness). An incandescent lamp can be made more energy efficient (more light, or lumens. per watt) but its lifetime would be reduced significantly. Likewise, its life could be extended dramatically by reducing the lamp voltage 10-20% but the light would become more “yellow”.

It took nearly 50 years after Edison’s early work in the nineteenth century for the incandescent lamp to really become widely popular and even then most of lighting applications which now exist were not even imagined. In the 1930’s, folks had few light bulbs in the home, electricity was very cheap and the few bulb types needed could be bought at the general store. In fact, for nearly 50 years the 40, 60 or 100 watt bulb went a long way toward meeting 90% of America’s needs and light bulb manufacturers justifiably created a set of design guidelines as a common denominator for all needs. Today all those factors are quite different, but the bulb has remained the same, for volume manufacturability.

Gaseous Discharge Lamps

Gaseous discharge covers neon, low-pressure sodium, fluorescent and high intensity discharge (HID lamps). Within the HID category, there are Mercury Vapor, Metal Halide, Induction and High Pressure Sodium types.

For the sake of simplicity we’ll bypass a discussion of neon (known best for signs) and low pressure sodium (which has fallen out of favor because of its extremely poor color rendering (it makes everything look brown). All gaseous discharge lamps operate on the principle that a controlled “arc-over’ must be created across the length of the gas-filled tube. This “ignition” is facilitated by a ballast (which may be of either the autotransformer or electronic type) to create a momentarily high starting voltage. (Consider a gaseous-discharge lamp to be a fancy version of a sparkplug in a vacuum bottle)

The fluorescent lamp principles were discovered in the 1800’s but not refined into commercially useful form until the 1930’s and, early on, by GE. The fluorescent lamp is noted for its exceptional energy efficiency and long life. Generally having 5-6 times more lumens per watt than an incandescent, the fluorescent also can last 10-15 times longer. Unlike an incandescent, fluorescent lifetime is degraded by very frequent on/off switching and the attendant physical deterioration of the electrodes caused by that switching. A simplified explanation is that every time it is switched on, a microscopic amount of material gets knocked off the electrode.

Finally, fluorescent lamp lumen output is quite sensitive to temperature and even requires a higher ignition voltage to come on at all when temperatures drop substantially. But despite their shortcomings, the popular 4-foot fluorescent tube remains an extraordinarily cost-effective, energy efficient light source for larger indoor areas.

The high-pressure mercury vapor lamp was an extension of the basic fluorescent lamp. A much smaller arc, under high pressure and higher temperature, allowed a much more compact, higher power lamp to be created. Fifty years ago, the mercury vapor streetlight became commonplace, in spite of its less than desirable bluish tint. Like the fluorescent, it provided over 5 times the energy efficiency and 15 times the life of an equivalent incandescent bulb. Consequently, it’s no surprise that many municipalities and factories moved toward these lamps.

But, unlike fluorescents, mercury vapor lamps have a 5 minute or more warm-up period and when turned off, must first cool down before being receptive to turn-on again.

That delay, called the “re-strike” time, is caused by the very hot gas requiring a far higher ignition voltage than the ballast has been designed for. After some cooling, the required ignition voltage drops to where the lamp can operate.

The inconvenience caused by long warm-up and re-strike delays has dogged the HID industry for decades and has prevented these extraordinarily efficient, compact, long-life lamps from being used in far more places. The mercury vapor lamp also has carried the baggage of having that bluish tint, which has been an issue when good color rendering has been desired.

Metal halide lamps are an extension of the mercury vapor lamps and have a gas mixture to create emission more resembling daylight. These lamps have more complex chemistry in how the light is created and how the ballast must control the arc. The metal halide lamp has essentially replaced the mercury vapor lamp today wherever good color rendition is appropriate, as in a large new car lot or “big box” store environment where it is desired to accurately show clothing colors.

In fact the metal halide lamp is increasingly becoming the choice over high pressure sodium (HPS) for street and parking lot lighting.

The high pressure sodium lamp in the 90’s became king of the hill for streetlights, sports complexes, warehouses, parking lots etc. They exhibit unmatched energy efficiency (up to 10 times that of incandescent lamps and longevity up to 20 times more. They are available with up to 1,000 watt ratings and have been improved over the years so that the yellow tint is much less noticeable and certainly not even remotely as color unfriendly as low pressure sodium or neon light sources.

As with all HID’s, however, these lamps have a re-strike issue so they can only be used where they are always on or, as a street light, only get one cycle per day and are often being replace by metal halide.

Over the years some firm developed “instant re-strike” HID lamps whereby special ballasts and unique bulb designs could allow extremely high voltage to strike the lamp even when the gas was very hot, as just after turn off. Today, some low power (under 75 watt) versions are available with special electronic ballasts (circuitry) in order to turn the lamp back on, not instantly but to near full brightness in a faction of a minute… obviously still not fast enough for general lighting.

In recent years there has been some attention given to what are called “induction lamps” These are basically “electrode-less” HID lamps which the gas is ionized by RF energy rather than a direct electrical connection. The actual characteristics of these lamps have been well known for over 60 years. They basically are fluorescent lamps in which the internal gas is ionized by an external RF filed rather than by an arc between internal electrodes

Even personnel at military radar installations observed 50 years ago that fluorescent lamp tubes, left on the floor in a radar dome near a rotating antenna, would ionize and, even without an electrical connection, “light up” every time the antenna came around.

Introduced almost 20 years ago, induction lighting fixtures have never really gained significant traction because of cost and other limitations. With higher power, more versatile LED lighting on the horizon, it appears that induction lighting has missed its “opportunity window” and will less and less be a candidate for mainstream applications.

Solid State Lighting

There are several types of solid state lamps in use, with electroluminescent (EL) and light emitting diodes (LEDs) being most familiar, and the new LED structures called Organic LEDs (OLEDs). We will focus on the LED, and more specifically, “inorganic” semiconductor chip-based technology but it’s worth at least noting the other two because they fill some special market niches which their solid-state cousins may be less well-suited for.

Electroluminescent (EL) light sources have been around for well over 45 years but are related to special purpose indicators where power consumption is important but light intensity is usually not. Suffice it to say that the EL lamp is a kind of film capacitor that has its surface light up in proportion to the amplitude and frequency of a voltage impressed across it. Aircraft exit signs used this technology for many years.

OLEDs are created with a kind of thick film printing of crystalline substances. These devices, for now, relegated to low power large area applications but nevertheless destined for possible success in certain types graphic displays.

While OLEDs have received attention in academic and specialty areas, it has means there increasing awareness that their high cost and performance limitations means they can be used for select purposes but hardly will be the “next big thing” for mainstream illumination when compared against conventional “inorganic”LED product.