What is SSL technology?

Solid-state lighting (SSL) technology is the broad term for a light source, using semi-conducting materials to convert electricity into light.

What Does L.E.D stand for?

Light-Emitting Diode

What Does O.L.E.D stand for?

Organic Light-Emitting Diode

What Does P.L.E.D stand for?

Polymer Light-Emitting Diode

What is an LED?

An LED is a semi-conducting device that produces photonic energy when an electrical current flows through it.

What is the difference between LED’s and other traditional forms of lighting?

The difference is in the fundamental way the lamps produce light.

LED Lighting - When an LED is forward biased (switched on), electrons recombine with electron holes (missing electron in an atom or atomic lattice) within the device, releasing energy in the form of photons (light). This effect is called electroluminescence.

LED’s are small and produce very little heat compared to other traditional forms of illumination. LED’s also do not have large amounts of hazardous substances such as mercury and have much less impact on the environment.

Incandescent Lighting - A tungsten filament is heated by an electric current until it glows or emits light. As the lamp is used the filament evaporates shortening the life of the lamp and eventually “burns out.” Fluorescent Lighting - Electric energy excites mercury vapor, which emits ultraviolet light that reacts with the phosphor coating on the inside of glass tubes causing it to fluoresce. These fixtures require a ballast to regulate the current going through the lamp. The lamps contain mercury vapor which is a hazardous chemical.

Combustion Lighting – Otherwise known as an open flame where fuel is burned producing light such as a candle, or kerosene lamp. Light output is low and temperature is high. It is not considered a viable source of light except in accent lighting or certain mood effects.

How does an LED work?

An LED consists of a chip of semiconducting material treated to create a structure called a p-n (positive-negative) junction. When connected to a power source, current flows from the p-side or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers (electrons and electron holes) flow into the junction from electrodes. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon (light).

When were LED’s invented?

LED’s were first developed in the 1960’s but were used only in indicator applications until recently.

The electronics industry has used LED technology for several decades as indicator lights for various electronic devices. In more recent years, LED technology has progressed to the point where it is viable for general lighting applications.

Why LED's?

As a rule, LED bulbs use 90% less electricity than standard bulbs. They have an unparalleled even spectrum of light and have a lifespan beyond ten years. LED's provide us the most efficient way to save energy and conserve our natural resources. If LED's were implemented right now, universally we would not need to build another power plant. LED’s would actually eliminate the need for over 30 existing power plants!

How do LED’s emit different color?

The specific wavelength or color emitted by the LED depends on the materials used to make the diode. Red LEDs are based on aluminum gallium arsenide (AlGaAs). Blue LEDs are made from indium gallium nitride (InGaN) and green from aluminum gallium phosphide (AlGaP). "White" light is created by combining the light from red, green, and blue (RGB) LED’s or by coating a blue LED with yellow phosphor.

What are Low Power LED’s?

Low power LED’s commonly come in 5 mm sizes, although they are also available in 3 mm and 8 mm sizes. These are fractional wattage devices, typically 0.1 watt, they operate at a low current (~20 milliamps) and low voltage (3.2 volts DC), as well as produce a small amount of light, perhaps 2 to 4 lumens.

What are High Power LED’s?

High power LED’s come in 1-3 watt packages. They are driven at a much higher current, typically 350, 700, or 1000 mA, and—with current technology—can produce 40-80 lumens per 1-watt package.

Where have LED’s been used in the lighting industry?

LED’s are commonly used in aesthetic, effect, or specialty lighting applications, including architectural highlighting. Most traffic lights and exit signs, for example, now use red, green, or blue LED’s.

Have LED’s always been used in general illumination lighting?

No. Early attempts to apply LED’s in general illumination lighting failed because they did not meet the lumen-per-watt output or color requirements. Technology has advanced however, to the point where using LED’s for general illumination is now viable. Lighting industry experts are now gaining a better understanding of how to capitalize on that technology.

Why have past attempts to create general illumination LED’s failed?

Conventional approaches to developing general illumination LED’s often involved retrofitting existing fixtures to house the new LED technology. Instead of investigating the benefits and challenges of LED’s, many early attempts simply used traditional lighting standards and housings. The problem was that LED technology breaks all traditional rules, and it quickly became apparent that old thinking could not be applied to this new technology. Long-term research and development goals call for white-light LED’s producing 160 lm/W in cost-effective, market-ready systems by 2025. In the meantime, how does the luminous efficacy of today's white LED’s compare to traditional light sources? Currently, the most efficacious white LED’s can perform similarly to fluorescent lamps. However, there are several important caveats, as explained below.

Why do LED’s not function as efficiently in traditional fixture housing?

An LED module may physically fit into an existing housing, but that housing does not leverage the inherent qualities of the LED’s. Standard housings cannot handle the challenges of LED thermal management, which is vastly different than thermal management for traditional incandescent or fluorescent lighting. Also, the optical design used in most traditional fixtures doesn't maximize the LED's efficiency.

What are the advantages to using LED lights?

LED’s bring several advantages to the lighting industry, including high efficiency and durability, and, with superior life over other lamp sources; their required maintenance is greatly reduced. This translates into energy savings, maintenance savings and an overall reduction in cost of ownership over the product's lifetime.

Do I have to replace LED diodes?

An LED does not burn out like a standard lamp, so individual diodes do not need to be replaced. Instead, the diodes gradually produce lower output levels over a very long period of time. If one LED fails, it does not produce a complete fixture outage.

What is Phosphor Conversion?

Phosphor conversion is a method used to generate white light with LED’s. A blue or near-ultraviolet LED is coated with a yellow or multichromatic phosphor, resulting in white light.

What is luminous efficacy?

Luminous efficacy is a typically used measure of the energy efficiency of a light source. It is stated in lumens per watt (lm/W), indicating the amount of light a light source produces for each watt of electricity consumed. For white high-brightness LED’s, luminous efficacy published by LED manufacturers typically refers to the LED chip only, and doesn't include driver losses.

What is CCT?

Correlated color temperature (CCT) is the measure used to describe the relative color appearance of a white light source. CCT indicates whether a light source appears more yellow/gold/orange or more blue, in terms of the range of available shades of "white." CCT is given in kelvins (unit of absolute temperature). See more information in the Color Quality section.

What is CRI?

Color rendering index (CRI) indicates how well a light source renders colors of people and objects, compared to a reference source.

What is the difference between efficiency and efficacy?

Efficacy is a term normally used in cases where the input and output units differ. In lighting, we are concerned with the amount of light (in lumens) produced by a certain amount of electricity (in watts). On the other hand, efficiency is a term that is typically dimensionless. For example, lighting fixture efficiency is the ratio of the total lumens exiting the fixture to the total lumens initially produced by the light source. "Efficiency" is also used to discuss the broader concept of using resources efficiently.

What is lumen?

The SI unit of luminous flux, the total amount of light emitted by a light source, without regard to directionality, is given in lumens.

What is luminaire efficacy?

The total luminous flux emitted by the luminaire divided by the total power input to the luminaire, expressed in lm/W.

What is general illumination?

General illumination is a term used to distinguish between lighting that illuminates tasks, spaces, or objects from lighting used in indicator or purely decorative applications. In most cases, general illumination is provided by white light sources, including incandescent, fluorescent, high-intensity discharge sources, and white LED’s. Lighting used for indication or decoration is often monochromatic, as in traffic lights, exit signs, vehicle brake lights, signage, and holiday lights.

What is energy efficiency?

Energy efficiency of light sources can be characterized in several different ways. Luminous efficacy indicates how much light the source provides per watt of electricity consumed. This is stated in lumens per watt (lm/W). Another measure of energy efficiency is the total watts a device consumes in providing the intended service. Both measures are important to consider. For example, an LED-based refrigerated display case light has lower lumens per watt compared to linear fluorescent systems, but uses about half the total watts to provide the necessary lighting.

What is lighting quality?

Lighting quality is a subjective term, but generally includes color quality (including appearance, color rendering, and color consistency); luminance levels (the amount of light the light source provides on a task or surface); photometric distribution of the light source in a fixture or luminaire; lifetime; ease of maintenance; and cost.

What is a driver?

Fluorescent and high-intensity discharge (HID) light sources cannot function without ballast, which provides a starting voltage and limits electrical current to the lamp. LED’s also require supplementary electronics, usually called drivers. The driver converts line power to the appropriate voltage (typically between 2 and 4 volts DC for high-brightness LED’s) and current (generally 200-1000 milliamps or mA), and may also include dimming and/or color correction controls.

What is driver Loss?

Currently available LED drivers are typically about 85% efficient. So LED efficacy should be discounted by 15% to account for the driver. Fluorescent and high-intensity discharge (HID) light sources cannot function without ballast, which provides a starting voltage and limits electrical current to the lamp. LED’s also require supplementary electronics, usually called drivers. The driver converts line power to the appropriate voltage (typically between 2 and 4 volts DC for high-brightness LEDs) and current (generally 200-1000 milliamps or mA), and may also include dimming and/or color correction controls.

How do you evaluate LED products?

Lumen output is only part of the story and can be misleading. To fully evaluate an LED product one needs to review the overall system efficiency, optical control, thermal management of the LED’s, and know at what point in time the fixture will reach 30 percent lumen depreciation. Products with good optical efficiency and thermal management will be able to deliver more lumens, on average, than traditional HID products. As the Department of Energy concluded in its Solid-State Lighting Commercial Product Testing Program: "Until the field of SSL technologies and supporting knowledge matures, any claims regarding performance of SSL luminaires should be based on overall luminaire efficacy (i.e., from testing of the entire luminaire, including LEDs, drivers, heat sinks, optical lenses and housing), to avoid misleading buyers and causing long-term damage to the SSL market."

How do you evaluate LED products?

A full evaluation of an LED product includes: reviewing the overall system efficiency, optical control, thermal management of the LEDs, and determining at what point in time the fixture will reach 30% lumen depreciation. Products with good optical efficiency and thermal management will be able to deliver more lumens, on average, than traditional HID products.

As the Department of Energy concluded in its Solid-State Lighting Commercial Product Testing Program: "Until the field of SSL technologies and supporting knowledge matures, any claims regarding performance of SSL luminaires should be based on overall luminaire efficacy (i.e., from testing of the entire luminaire, including LEDs, drivers, heat sinks, optical lenses and housing), to avoid misleading buyers and causing long-term damage to the SSL market."

How are LEDs able to outperform HIDs?

In contrast to traditional HID luminaires, super-bright white LEDs have the advantage of minimal lumen depreciation, better optical efficiency and high lumens per watt. LEDs also have a vastly longer life span than traditional lamp sources.

The fixtures must be designed to leverage these inherent advantages of LEDs. Therefore, A Total Systems Approach is needed for an LED product to bring all of these features together.

Additionally, LED fixtures have an environmental advantage over traditional light sources as they contain no mercury, last longer, produce less waste, and are made from fully recyclable materials. Furthermore, the extruded aluminum heat sink is manufactured using 77% post-industrial recycled material.

If an LED fixture has a lower initial lumen output than a traditional HID light, how can LEDs claim to deliver lumens more efficiently than HIDs?

It has been showed that an LED light outperforms a 400-watt MH lamp operated in a horizontal position on average in a time period of 60,000 hours. (60,000 hours represents three full life cycles of the HID.)

THE MH’s lumen depreciation, as well as optical and ballast losses, quickly reduce output of the HID system. Note that there are three relamps (lamp replacements?) over 60,000 hours.

Conversely, LED has significantly better lumen maintenance and a more efficient driver. Also note that the LED fixture typically doesn’t need relamping (lamp replacements?) for zero to 60,000 hours.

Combine this with Beta’s exclusive NanoOptic and LED outperforms MH over the course of the life the fixture. The result of the test was that LED’s averaged 74% higher lumens than HID over 60,000 hours.

How do you compare LED sources to traditional light sources?

Energy efficient proponents are accustomed to comparing light sources on the basis of luminous efficacy. To compare LED sources to CFLs, for example, the most basic analysis should compare lamp-ballast efficacy to LED + driver efficacy in lumens per watt.

Data sheets for white LEDs from the leading manufactures will generally provide “typical” luminous flux in lumens, test current (mA), forward voltage (V), and junction temperature (Tj), usually 25 degrees Celsius. TO calculate lm/W, divide lumens by currents time the voltage. As an example, assume a device with a typical flux of 45 lumens, operated at 350 mA and voltage of 3.42 V. The luminous efficacy of the LED source would be: 45 lumens/ (.35 amps X 3.42 volts) = 38 lm/W

To include typical driver losses, multiply this figure by 85%, resulting in 32 lm/W. Because LED light output is sensitive to temperature, some manufacturers recommend de-rating luminous flux by 10% to account for thermal effects. In this example, accounting for this thermal factor would result in a system efficacy of approximately 29 lm/W. However, actual thermal performance depends on heat sink and fixture design, so this is only a very rough approximation. Accurate measurement can only be accomplished at the luminaire level.

What is application efficiency?

While there is no standard definition of application efficiency, we use the term here to denote an important design consideration: that the desired level of illumination and lighting quality for a given application should be achieved with the lowest practical energy input. Light source directionality and intensity may result in higher application efficiency even though luminous efficacy is lower relative ot other light sources.

How does ambient temperature affect LED efficiency?

LED fixtures must be designed with junction temperature thermal management as a key component and use the correct LEDs. These products will then be robust enough to operate in most ambient temperature applications. Unlike fluorescent sources, cold temperatures do no t impact the performance of LEDs.

What is junction temperature?

Junction temperature is the temperature point at which an individual diode connects to its base. Maintaining a low junction temperature increases output and slows LED lumen depreciation. Junction temperature is a key metric for evaluating an LED product’s quality and ability to deliver a long life.

The three things affecting junction temperature are: drive current, thermal path, and ambient temperature. In general, the higher the drive current, the greater the heat generated at the die. Heat must be moved away from the die in order to maintain expected light output, life, and color. The amount of heat that can be removed depends upon the ambient temperature and the design of the thermal path form the die to the surroundings.

The Department of Energy advises: "Heat management and an awareness of the operating environment are critical considerations to the design and application of LED luminaires for general illumination. Successful products will use superior heat sink designs to dissipate heat, and minimize junction temperature. Keeping the junction temperature as low as possible and within manufacturer specifications is necessary in order to maximize the performance potential of LEDs."

Why is the life span of an LED measured through lumen depreciation?

The life span of an LED is vastly longer than that of incandescent, fluorescent or HID lamp sources, generally lasting 50,000 hours or longer. Because the LED never really burns out, product life span is measured by lumen depreciation. The Illuminating Engineering Society’s (IES) current standard for calculating the life of an LED is that its lifespan is over at the point when the LED reaches 30% lumen depreciation.

Remember, a 100,000-hour rating is not equivalent to lamp life rating. LED life is rated where it has reached 30% lumen depreciation. At 100,000 hours an LED would still be operating, but at a decreased lumen output.

How long is 50,000 hours?

Based on how long a fixture is illuminated per day, here's what 50,000 works out to:

50,000 Hours of Operation is:

24 hours a day= 5.7 years

18 hours per day =7.4 years

12 hours per day= 11.4 years

8 hours per day =17.1 years

Do LED light bulbs contain mercury?

No. LED bulbs do not contain mercury. They can actually be recycled as they do not contain hazardous substances and are manufactured without hazardous substances.

What is an OLED?

Organic light-emitting diodes (OLEDs) are based on organic (carbon based) materials. In contrast to LEDs, which are small point sources, OLEDs are made in sheets which provide a diffuse area light source. OLED technology is developing rapidly and is increasingly used in display applications such as cell phones and PDA screens. However, OLEDs are still some years away from becoming a practical general illumination source. Additional advancements are needed in light output, color, efficiency, cost, and lifetime.

Light and Color Basics

Light-emitting diodes (LEDs) differ from other light sources, such as incandescent and fluorescent lamps, in the way they generate white light. We are accustomed to lamps that emit white light. But what does that really mean? What appears to our eyes as "white" is actually a mix of different wavelengths in the visible portion of the electromagnetic spectrum.

The diagram below illustrates visible light as one small portion of the overall electromagnetic spectrum.

Electromagnetic radiation in wavelengths from about 380 to 770 nanometers is visible to the human eye. Incandescent, fluorescent, and high-intensity discharge (HID) lamps radiate across the visible spectrum, but with varying intensity in the different wavelengths. The spectral power distribution (SPD) for a given light source shows the relative radiant power emitted by the light source at each wavelength. Incandescent sources have a continuous SPD, but relative power is low in the blue and green regions. The typically "warm" color appearance of incandescent lamps is due to the relatively high emissions in the orange and red regions of the spectrum.

SPDs for fluorescent and HID sources are provided for comparison. These sources have "spikes" of relatively higher intensity at certain wavelengths, but still appear white to our eyes. Unlike incandescent, fluorescent and HID sources, LEDs are near-monochromatic light sources. An individual LED chip emits light in a specific wavelength. This is why LEDs are comparatively so efficient for colored light applications. In traffic lights, for example, LEDs have largely replaced the old incandescent and colored filter systems. Using colored filters or lenses is actually a very inefficient way to achieve colored light. For example, a red filter on an incandescent lamp can block 90% of the visible light from the lamp. Red LEDs provide the same amount of light for about 1/10 of the power (12 watts compared to 120+ watts) and last many times longer. However, to be used as a general light source, "white" light is needed. LEDs are not inherently white light sources.

What is lumen depreciation?

All types of electric light sources experience lumen depreciation, defined as the decrease in lumen output that occurs as a lamp is operated. The causes of lumen depreciation in incandescent lamps are depletion of the filament over time and the accumulation of evaporated tungsten particles on the bulb wall. This typically results in 10% to 15% depreciation compared to initial lumen output over the 1,000 hour life of an incandescent lamp.

In fluorescent lamps, the causes of lumen depreciation are photochemical degradation of the phosphor coating and the glass tube, and the accumulation of light-absorbing deposits within the lamp over time. Specific lamp lumen depreciation curves are provided by the lamp manufacturers. Current high quality fluorescent lamps using rare earth phosphors will lose only 5-10% of initial lumens at 20,000 hours of operation. Compact fluorescent lamps (CFLs) experience higher lumen depreciation compared to linear sources, but higher quality models generally lose no more than 20% of initial lumens over their 10,000 hour life.

Lumen depreciation in LEDs varies depending upon package and system design. The primary cause of lumen depreciation is heat generated at the LED junction. LEDs do not emit heat as infrared radiation (IR) like other light sources, so the heat must be removed from the device by conduction or convection. If the LED system design has inadequate heat sinking or other means of removing the heat, the device temperature will rise, resulting in lower light output. Clouding of the epoxy encapsulant used to cover some LED chips also results in decreased lumens making it out of the device. Newer high-power LED devices use silicone as an encapsulant, which prevents this problem. LEDs continue to operate even after their light output has decreased to very low levels. This becomes the important factor in determining the effective useful life of the LED.