TAM L I T E LI G H TI N G
LED lighting is the greatest development in the lighting industry since Thomas Edison presented the world with an electric lamp circa 1880.
With all the talk about LED it feels like a new technology but it has actually been around for more than half a century. The LED started life in October 1962, as a single red illumination in a General Electric research lab in New York. During the early years, from 1970 onwards LED quickly established itself for use in a variety of application mainly as indicator
lights or numerical displays on measuring instruments. Throughout the 1970s LEDs were used in watches, calculators, electronics and traffic lights with red LEDs in Emergency lighting. In the early part of the 1990s a breakthrough was made by an engineer at the Nichia corporation which resulted in a blue LED being available. For the first time white light was made possible by the careful combination of RED, GREEN and BLUE LEDs: the 3 primary colours of light. By 1996 phosphor white LEDs had been developed allowing white LED light to be created with a single blue LED and a phosphor coating. For the early part of the 21st century there was significant development in the efficiency of LEDs.
First red LED developed by Nick Holonyak at GE in 1962 Red indicator LEDs manufactured by HP, with materials from Monsanto - 0.1 lm First green and yellow LEDs
First blue LEDs arrive in 1971 1 lumen red LEDs available by 1972 LEDs used in watches, calculators, traffic lights and exit signs
Advances in lumen output. 1984: First Superbright red LEDs
High-brightness blue LEDs by Shuji Nakamura at Nichia in 1993 1995: High-brightness green LEDs First white LEDs developed in 1996 Ultrabright red and amber LEDs LEDs begin to replace incandescent sources in coloured light applications LEDs become viable for portable illumination applications Colour Kinetics founded in 1997 1998: RGB lighting applications
White light via RGB LEDs White light via blue + phosphors First â€œtunableâ€? white LED luminaires LEDs available in 10-100 lumens By 2003, LEDs widely accepted in entertainment lighting applications White-light LEDs become viable for accent lighting by 2004 1000+ lumen LEDs via multi-chip packages available by 2005 By 2008, LEDs become viable for general illumination Multiple manufacturers (Nichia, Cree, Osram, Lumileds, King Brite, Cotco etc)
Introduction How LEDs work ‘LED’ stands for Light Emitting Diode which is a type of semi conductor. A semiconductor is made up of two elements (referred to as N & P type) that have no free electrons and therefore do not conduct electricity. Through a process of “doping” which involves adding an impurity into the chain that has free electrons, the N type material is negatively charged and the P type material is positively charged.
The materials selected determine the wavelength of the released photons and ultimately the colour of the light emitted. This process produces heat at the P-N junction. Controlling the temperature at the junction with a well designed heat sink and other thermal management is very important and ultimately determines the performance and life of the LED.
The creation of free electrons on one side (N type) and free holes for them to slot into on the other side (P type) is the basic electronic fundamental behind LED lighting. The two materials are separated by a junction and when a current is applied to the diode the atoms in the P and N type material move towards the junction, when they get close enough the N type atoms “donate” their free electrons to the P-type atoms. Applying a negative charge to the N-type side of the diode allows current to flow from one side to the other. The “donated” electrons move around and fall into the free holes, during this process they release energy in the form of photons. These photons release their energy as light in a process known as photophosphorescence.
P Type material
N Type material
How LEDs are built The construction of LEDs used in today’s lighting products is slightly different to the indicator LEDs that have been made for panel displays and other electronic devices for many years. The basic core of an LED is the semiconductor chip (or die) built on a substrate. This is then powered via contacts and a bond wire. Then a heat sink is needed to maintain the correct thermal dynamics within the die, and finally an outer casing provides mechanical protection.
LED Construction There are 2 basic types of LEDs used in luminaire production, both using the basic construction principles outlined above. SMD SMD (surface mount-device)-Involves mounting the chips (or chips) onto a printed circuit board (PCB) that already has an electronic power circuit etched into the board. The LED chips are placed on the board by an automatic mounting machine in a pre-arranged pattern. The power is fed to all chips via the PCB and power is then fed separately to the board. The individual chips are usually all of an identical format and performance, and have their own individual optical characteristics. COB COB (chip-on-board) differs from SMD in both the build and appearance. The chips are placed onto a substrate but the power connections are applied at the same time. A number of different chips can be used to build a large (often 25-50mm square) assembly. The power is then applied via bond-wires to the whole assembly and a separate phosphorescence coating is usually applied to the entire assembly, hence the yellow â€˜blobâ€™ associated with COB devices.
reproduced by LEDs. Different colours (white, red, blue, green etc.) are created by the use of different materials in the construction of the LEDs as these different materials emit light at different frequencies. The mixing of different colour LEDs can now also create very small differences in shades of colours as well as control the different shades of white in modern commercial luminaires. This method is known as the additive colour model. In theory a RED, GREEN and BLUE LED mixed to the exact same intensity and quantity would produce a pure white colour, as these colours are the basic colours in this model. Subtle changes to the power and quantity within the design can create equally subtle changes to either white or other solid colours. For many LED devices the various shades of white can be created with the careful use of phophors, thereby utilising only one LED. This colour correction has been used with fluorescent lamp sources for many years to create the warm, neutral or cool white lamps used in commercial, retail and industrial luminaires.
Creating white light Technological advances in the design of LEDs and the introduction of new materials mean that virtually any colour can be
For the LED to be used for illumination it needs to be integrated into a system that incorporates optics, LED drivers and thermal management
Optics Most modern LEDs emit light from a much smaller surface area when compared to conventional light sources. Quite often the light output is similar to a T5 or T8 fluorescent tube but the light is being emitted from a device that is only 10 or 20% of the size. So, controlling and managing this glare is a major issue for luminaire manufacturers. Optics can come in various formats such as reflectors, diffusers and lenses and are used to direct the light and reduce the glare. Lenses Plastic lenses can be used to direct and diffuse the light from an individual chip or array. Reflectors Reflectors re generally used in conjunction with other LED optics to help re-direct light to the most critical of areas. This is often done for luminaires where the LEDs are not directly visible.
Diffusers Many luminaires incorporate a large diffuser panel to reduce the glare of a large LED array. This is often a cheaper method but will reduce the light output of the luminaire from the original LED light output.
Drivers Most LEDs operate at voltages below 50V and therefore need a device that converts mains voltage and provides a stable power supply. The driver protects LEDs from voltage fluctuations as well as from over voltages and voltage spikes. Most drivers are remote from the LED boards and have means to connect a mains supply and then a simple connector to provide power to the device. Drivers can be supplied as dimmable and addressable to fit in to many lighting control systems.
Heat Sinks The basic fundamental principle behind LEDs (as outlined in the Introduction section) creates a transference of heat that can badly damage the performance of LEDs (light and life) if it is not managed correctly. The impact of a badly managed thermal system is far more damaging for a LED luminaire than it is for traditional halogen or fluorescent systems. LED chip manufacturers measure the lumen output of their LEDs using a 15-20millisecond power pulse where the junction temperature is fixed in a controlled laboratory setting. So in reality the lumen output supplied by chip manufacturers will differ once the LEDs are packaged and assembled inside a luminaire, and the actual junction temperature will depend on the drive current, thermal path and ambient temperature. So LED luminaire outputs must not be collated from chip manufacturers data sheets.
Output Light output is seriously affected by very small increases in the junction temperature of LED devices. The graph below (fig 1) illustrates this. The design of each part of a LED device, from the substrate through to the luminaire housing, is critical in making sure that heat is removed from the junction and the published light output figures are correct. Life As well as having a significant impact on the light output, the life of a LED will fall drastically without a suitable thermal design. Failure rates of essential components are very dependent on the ambient and junction temperature so appropriate materials and designs have to be used. Fig 1. Indicates how various colour LEDs respond to
operating at typical temperature within luminaires.
Typical application temperatures
Fig 1. 200% Percentage of luminous flux relative to measurement at 25 ยบC
150% Green 100%
Junction temperature TJ (ยบC)
STANDARDS AND TESTING The introduction of LED technology has required new tests and standards that now sit alongside existing established requirements
Life Life time of conventional light sources (Fluorescent, HID, CFL) are usually published based on when the lamp will fail. Typically this is measured when 50% of a batch of lamps on test have failed. In a T8 fluorescent lamp this lifetime rating would have been around 12,000-15,000 hours. Lifetimes of LEDs are much higher but the method for determining this life is different. At 50,000 hours a typical, branded LED module will have at least half of itâ€™s chips giving 70% of itâ€™s initial light output. A drop below this level would be considered unsuitable for most applications as the lighting levels would be under most design standards that were used when the initial design was completed.
A real life test would take in excess of 5 years and by that time the product is out of date. The current UK standard test has been developed by the IES. LM-80 requires testing of LED light sources for 6,000 hours at three different junction temperatures to show the effects of temperature on light output. A further standard (TM21) then outlines how this data can be used to predict long-term life. But as absolute failure is very rare the testing for life is now based on the length of time it takes for the light source to reach 70% of their initial output. This is known as L70. This life can also vary depending on the junction temperature. Outputs must not be collated from chip manufactures data sheets.
Fig 2. The B10 and B50 graphs show aspects of lumen maintenance at current life and T life 100% B50
18W T8 B10
30,000 Operating lifetime (hours)
Standards and testing.
Output As with many light sources the output of a LED will decrease throughout its life. There are many factors which will contribute to this decline: - Excess heat at junction - Excess ambient heat - Increase in supply current Many outputs listed by luminaire manufacturers will list the output (lumens) of a LED module or chip rather than the actual light output of the luminaire (luminaire lumens). This can be very misleading as once a chip is mounted inside a luminaire then any of the above 3 factors can affect the output by up to 50%. This can be for a number of reasons. - - -
Poorly designed heat sink for chip mount Insufficient heat dissipation from module around luminaire housing Incorrect drive current used
As an example, increasing the junction temperature by 5ยบC can reduce the output (See Fig 3) of a LED chip by as much as 30%. This highlights another very good reason Fig 3. Effect of junction temperature on light output
why the management of heat within the circuit or luminaire is vital. The calculation used in determining the drop in output from an LED is called Lumen maintenance. This measures the rate of decline against time (in hours). A typical graph for a branded chip might look like this (see fig 2). The data shows that at least half of a sample batch of LEDs will emit 70% of their initial light output at 50,000 hours. Many traditional light sources would lose much more light in a much shorter time. The nature of many LEDs is such that complete failure is very rare. Hence, lifetime expectancy is now based around the drop in light output rather than complete failure. The term used to show what parameters have been used to calculate this decline is B50/L70 (i.e. 50% of the batch giving 70% of the light). In many low-end, unbranded chips the lifetime will be much lower and may not use this industry standard methodology.
90% 80% 70% 60% 50% 1,000 hrs T Junction at 74ยบC
T Junction at 63ยบC
Standards and testing.
Light Quality For many designers and installers the quality as well as quantity of light is vital in maintaining the correct lighting environment. This consideration has always played a huge part in good lighting design practice and it is still an important factor, even more so as many people look to replace existing, conventional lighting installations with LED. An improvement in life is no good if the quality of lighting is affected. There are 2 main considerations for qualifying the colour quality of all light sources and these 2 measures are now very useful for identifying quality LED products. The colour rendering index (CRI), is a measure of the ability of a light source to reproduce the colours of various objects faithfully in comparison with an ideal or natural light source. Light sources with a high CRI are desirable in colour-critical applications such as photography and cinematography as well as printing and even retail applications. It is defined by the CIE. In conventional terms, halogen and tri-phosphor fluorescent tubes have provided the highest indexes available.
Standards and testing.
The CRI of a light source does not indicate the apparent colour of the light source itself. That is classified by the colour correlated temperature (CCT). This defines the colour appearance (colour temperature) of the light source. It can range from a very warm, yellowish appearance (2500K) to a very cold, almost blue appearance (6500K). Lamp source
White (Neutral White) 3000-4500 Cool White
The advances in LED technology now enable for LED chips to be produced within any CCT(K) range. Care must be taken with the quality of the chip to ensure that all of the chips on an array or board all have the same colour temperature, otherwise a luminaire may well have warm-white spots within a cool-white array or even warm white luminaires alongside cool white luminaires. This process of ensuring that each chip within a large production run has matching colour
appearance is called binning. The chips are carefully measured as they come off the production lines and then automatically sorted into a â€˜binâ€™ depending on the results of the analysis. This ensures customers will get a consistent colour temperature across modules, luminaires and then installations.
Efficacy Many customers are selecting LEDs for the energy-saving benefits they can provide. As the range of LEDs available grows then the use and benefits can be extended to many different areas. In order to secure the best energy savings it is vital that customers understand the calculations behind some of the headline numbers often used to promote LED luminaires. Any light source can be classified by its ability to produce a certain amount of light for every watt of energy (power) used. The ratio of light to energy is called efficacy and has been a vital factor in lighting design for many years. Typical efficacies of conventional light sources are listed below
Fluorescent (halo+ magnetic)
Fluorescent (halo + electronic)
Fluorescent (tri + electronic)
It can be seen from this that there are existing conventional light sources that are just as energy-efficient as LED. There have been developments in fluorescent lamp technology to increase some of these efficiencies whilst LED also continues to improve. This data is only half of the story as the performance of the electronic circuit and the luminaire can then affect the light output. Firstly the LED chips are much more sensitive to ambient temperature or driver current than conventional fluorescent or discharge sources. Small changes in heat or current can greatly affect light output (and therefore efficacy). The performance of a luminaire is then crucial in making sure that all of the light produced by the light source ends up being used within the application or task area. If all of the light produced is lost within the luminaire then all the efficiencies gained are lost. The measurement that really matters then is the efficacy of the luminaire, or luminaire lumens/circuit watt. Many suppliers will quote LED chip outputs and wattages without then providing supporting photometric data that demonstrates the actual luminaire lumens. Gear (driver) losses can then affect the total circuit watts. Only independently tested photometric data and electrical characteristics (i.e. circuit power/W) should be used in determining the potential energy savings available from a LED lighting proposal. Standards and testing.
ACCENT lighting Applications
Office/Commercial Lighting (Fluorescent)
The advances in LED technology and LED luminaire design have brought the benefits of energy-saving, reduced maintenance and eco-friendly life cycles to many more end-users and designers.
The LEDs biggest competition in this area is the T5 lamp. Whilst the lumens per watt figures are ready to better that of T5 luminaires, glare and lighting controls are areas for consideration to luminaire designers. Use of computer screens means that glare must be kept to a minimum. With most offices now preferring to incorporate lighting controls such as presence and daylight detection, the additions of dimmable drivers along with expensive optics and thermal management of office specific LED luminaires can make paybacks difficult when compared with the T5 option available in the market.
LED lighting has already replaced a large proportion of GU10 and MR16 lamp sales, with equivalent outputs showing good energy savings. Many existing GU10 or MR16 Halogen lamps can be directly replaced with a new LED lamp that can offer an equivalent output (though not always against a brand-new replacement lamp) with energy savings up to 80%. CDMT and CFL luminaires (downlights and track spots) are now steadily being replaced by LED luminaires with similar outputs. Many retail customers are now enjoying the low-maintenance costs and modern looks that LED luminaires can offer.
For the greenest of customer LED will offer the best energy savings, but current return on investment calculations shows the T5 lamp on top, so both technologies will continue to be sold to different customer bases for the next few years.
Street lighting Street lighting is now at its tipping point with LED. Over the past 12 months or more local authorities have switched off discharge lighting during hours of the â€œnightâ€? (typically between 12.00am-5.00am) to save energy. They are now switching them back on and the future of street lighting will certainly be LED. Conditions for external applications in the UK mean that controlling the heat of LED lanterns is easy to manage. Lumens per Watt performance of LED provides energy and C02 savings The precise optical control of LED lanterns leads to accurate light distribution onto the road surface, with minimum light spill to surroundings or upward sky glow. Dimmable control gear will enable lanterns to be dimmed during less busy hours of the night, providing energy savings but greater safety, than switching lights off. Improved life spans also increase savings through reduced maintenance costs.
INDUSTRIAL ligh The existing lighting installed in many industrial applications is often a 400W HID lamp. Currently, it is difficult to achieve the same lumen outputs as such 400W luminaires with an LED light source. As mentioned earlier in the document, LED lighting performance is heavily dependant on thermal management. To achieve lumen outputs to rival the 400W HID lamp requires many high powered LEDs which in turn amounts to a large amount of heat being produced. So industrial lighting designers have a difficult task designing a luminaire with a sufficient lumen output and good thermal performance. At the time of publication, T5 fluorescent luminaires such as the Tamlite Lighting HILUX offering 4x80W luminaires with 26,000 lumens, 94% light output ratio, full daylight and presence detection, compound this challenge. At present it is difficult to see a return on investment using LED over T5 luminaires, but as the efficiency of LED increases and the cost falls it is only a matter of time.
RETAIL lighting The fast moving and ever-changing approach of design in Retail Lighting can benefit in many ways from the attributes of LED lighting. As with Accent and Display lighting, the high energy costs of Tungsten Halogen lamps have become the first casualty of the new technology, resulting in improvements in energy costs and reduction in maintenance through simple LED retro-fit solutions. As thermal designs improve and higher lumen outputs can be achieved, LED luminaires may now easily be used for illumination of larger areas in more demanding environments. Chip-on-board technology and improvement in thermal resistance has helped outputs from traditional track and recessed spotlights to be matched, if not beaten, with new LED luminaires. The need for colour consistency has always been an exacting demand on designers but LED and phosphor technology has now overcome this problem by much improved colour stability and binning, and high (>Ra90) levels of colour rendering, crucial for the modern retailer.
EMERGENCY ligh LED has had an important part to play in Emergency Lighting for many years as a charge indicator light source within traditional fluorescent or halogen emergency luminaires. But the advances in output, thermal management and control technology means that new solutions are available. The everyday fluorescent T5 emergency bulkhead can now be supplied with a highly efficient LED array to easily provide the minimum illumination requirements whilst also achieving significant long-term maintenance benefits. Traditional T5 lamps would need regular 2-3 years replacement programmes but the long-life benefits of LED means that they are a true â€˜fit and forgetâ€™ solution. Large area Emergency Lighting can also now be designed with the use of LED as a light source with traditional halogen emergency floodlights. As these are often installed at height, the cost and trouble of maintaining the low-life halogen lamps can be onerous. LEDs can now provide equivalent light output with the real saving in maintenance and ending disruption to workflow.
Life The speed of progress and development within the LED component market has
This performance standard covers 4 main aspects.
in turn created much quicker product development cycles within the luminaire industry. There are a number of new and complex facets for designers, installers, luminaire to
terminology, new data, new theories and new design concepts to consider. Tamlite
upon making our product offering clear, professional and trust worthy, and the advent of LED as a major light source for luminaires in all applications means the need to continue this strategy is key. We have now introduced the INFINITY ASSURANCE programme which will put in place a benchmark for performance that will give our customers the confidence and knowledge to make the right decision. The
- Light quality - Reliability - Efficacy - Assurance Light quality Minimum CRI (colour rendering index) >Ra80 Colour temperature tolerances and binning. SDCM <7 Reliability Minimum chip and driver failure rates of less than 2% for 6,000 hours, minimum lumen maintenance of 30,000 hours for L70/B50 criteria Efficacy Minimum performance of 70 luminaire lumens per circuit watt. Minimum power factor ratings on LED driver of 0.90
INFINITY ASSURANCE programme has been developed with our key component suppliers within the LED Lighting market to ensure customers can expect a minimum standard for performance from any of the LED luminaires which carry that mark.
Assurance Minimum 5 years warranty for absolute failure on driver, chip or luminaire. Full data and independent certification of all key, relevant standards
- LM-79 for output, colour quality and distribution - LM-80 for lumen maintenance Independent UK testing of luminaire performance and availability through the RELUX suite of design software. Tamlite Lighting have 45 years experience in the UK Lighting market and have invested significant sums in our UK manufacturing facilities to provide pre and after-sales service that is unrivalled within the industry.
Glossary Binning Sorting/classifying of (in this case) LEDs in groups with similar properties, e.g., with respect to colour temperature. CDM Ceramic discharge metal-halide lamp CIE Commission Internationale de l’éclairage / International Commission on Illumination Chromaticity colour coordinates Cold lumens Luminous flux measured at 25ºC junction temperature Diode Semiconductor or conducting electrical current very good in one direction, but not in the other direction. Downward light output The amount of the total luminous flux directed downward (in a horizontally suspended light source). Gamma or cut-off angle Angle in relation to the vertical as in a polar diagram Hot lumens Luminous flux measured at junction temperature close to practical usage temperature (typically 85ºC).
Junction temperature Temperature within the semiconductor material (at the PN junction– see below). LED Abbreviation for Light Emitting Diode. LED component Combination of LED, housing and primary optics. LED module The LED equivalent of a traditional lamp, but in LED version. According to ETAP’s terminology, this corresponds to type 3 - (see Section 1). Luminescence Process whereby a light particle (photon) is generated when an atom drops from a higher to a lower energy state. Luminous flux density The relation between the luminous flux flowing through the LED and its surface. Maintenance factor Factor with which pollution, ageing and lower light output of light sources are taken into account in lighting design calculations. PCB Printed circuit board. Remote phosphorus technology Technology whereby the phosphorus needed to generate white light is not put directly on the blue LED but in or on a (glass or plastic) support at some distance from the LED. As a result the phosphorus works at a lower temperature and can in some cases lead to increased efficiency. Substrate Support material on which the LED is secured together with the internal reflector. UGR Unified Glare Rating - this is an estimated model expressing the risk of glare. The standard values range from UGR 16 (low glare-risk) to UGR 28. Useful lifetime Economic lifetime relevant to the specific application, which is lower than the average lifetime.
Junction Active area in the solid state material in which the light is generated.
Ver 1.0 (Sept 2013)
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