Illuminance To Luminance

LED transformed the field of lighting design dynamically with reduction in equipment size but brighter light. It also frees the end-user from restriction – as to where lighting equipment can be installed. Lighting design is an emerging field in today’s landscape with depleting energy resources. The UNESCO has declared 2015 to be ‘the International Year of Light’ and – everyone hopes to see a renewed focus on light sources and lighting technologies for all spaces.

  In the inception stages, retail lighting focused on the basic need that customers should be able to see the products on display, that we term as general or ambient lighting that focuses on overall illumination. The focus then shifted to creating a lighting for specific tasks, example for activities such as reading, etc. Eventually, the retail premises have begun to build their own atmosphere, using light sources suiting to their needs, by using light sources and lighting to transform their spaces unlike others. The development of LED was vital as it took the focus away from task lighting to accent lighting.

  Panasonic has a history in developing the lighting technologies and light sources. Being the third largest lighting company in the world, its contribution to lighting arena is unparalleled than any other. Dr. Isamu Akasaki – one of the Nobel Prize winners of 2014 for the invention of Blue LED had worked for the Panasonic Tokyo Research Center, and his activities in that period contributed to the invention of the blue LED chip.

The new trends in LED signs and outdoor display include ‘Media Façade’ – where lighting is integrated into the front  surface of architecture...

  The Panasonic LED luminaires were introduced for retail premises in India in 2014, which include a range of professional luminaires that enable visual merchandising of the product for customer success. The company has more than 30,000 products in its LED portfolio.

  While the professional range of Panasonic luminaires helps create an environment offering optimum comfort and brightness, offering the best for accent lighting. From glareless wallwashers to elegant downlights to general lighting sphere products such as LED pendants to track lights, the range is globally renowned for retail lighting.

  The new trends in LED signs and outdoor display include ‘Media Facade’ – where lighting is integrated into the front surface of architecture. It is an emerging field in visual and spatial art that trounces over the structural limitation of unbending architecture with the colours of light – and enhances the value of the architecture. An example is illustrated above (page top). The said facade is located at Singapore Mall.

  Video 3D mapping is a projection technology used to turn objects, often irregularly shaped, into a display surface for video projection. These objects may be complex industrial landscapes, such as buildings. This technique is used by artists and advertisers. It is used to add extra dimensions, optical illusions, and notions of movement onto previously static objects primarily used for outdoor lighting. Example: mapping of the Bucharest Palace in Frankfurt on account of its 55th anniversary was done by Panasonic. Another one was done at the Marina Bay festival using Panasonic.

  The other format used for outdoor lighting is interactive lighting that one sees commonly at playzones in malls – where the audience interacts through light. This concept was beautifully presented by Panasonic in2011 at the Milano Salone del Mobile, the world's largest international furniture trade fair wherein Panasonic created the (standard)3 piano-forte, comprising of an interactive installation created in collaboration with the Italian designer Ferruccio Laviani.

  The biggest benefit that LED lighting offers in terms of saving is the energy-efficiency. LED lights offer optimum energy-efficiency, which means save over 90% of power consumption over incandescent light sources. The initial costing is high, however, on a long-term basis LED save not only the power, but also maintenance costs – as their operating life is an average 50000 burning hours – while incandescent light source lasts for about 1200 burning hours and a CFL lasts for about 8000 burning hours.

The biggest benefit that LED lighting offers in terms of saving is the energy-efficiency...

  Additionally, LEDs use less power (watts) per unit of light generated (Lumens), thus resulting in reducing greenhouse gas emissions from power plants and thereby lower electricity bills.

  LED light source comprises a chip encapsulated in resin enclosure and does not use fragile components – such as glass or filaments. Considering the rising costs of power an LED offers a long term saving over CFL or incandescent bulb – as though the initial cost is high, the risk of operation failure reduces by 99%.

  Additionally, LED offers more energy saving. It is environment-friendly as no mercury is used. It boasts instant-start feature. It is generally unaffected even if it is frequently switched on and off. The counterparts of LED i.e., CFL and incandescent lamps are bound to fail or obtain shorter lifespan during such operating conditions.

  The Indian market is very competitive in terms of LED lighting with global players looking for their share in the pie. Quality is considered secondary to cost, however, one should still look out for quality standards in LED such as safety approbations (UL, CSA, CE, ENEC, PSE, or SELV), and/or RoHS compliance should be considered for LED drivers that form the heart of the LED.

  As per a recent article, it is estimated that 88 billion litres of kerosene is burnt for light generation in the world each year.

  The new trend in LED lighting includes Solar LED lighting that is also propogated by UNFCC (The United Nations Framework Convention on Climate Change).

  Laser Lighting would probably be the next breakthrough in lighting, considering the fast paced Internet of Things (IoT) post Solar LED.

  Nobel laureate Shuji Nakamura, co-inventor of the blue Light-Emitting Diode (LED) has predicted that the power and sparkle of laser diodes that is presently used in some car headlights, will eventually replace LEDs, and become the dominant form of lighting, also increasing the availability and power of wireless communications networks based on light.

  “The modulation speed of Laser lighting being almost 1,000 times faster than LED lighting, would also help speed up Internet,” says Nakamura.

  The world of Wi-fi could change to Li-fi (the optical communications technology) that uses light instead of radio waves to transmit data at speeds of 3.5 Gbps or more – thus extending the application of laser diodes to boost communication.

  At the same time, one cannot ignore the changes brought about by the Internet of Things that has been instrumental in creating some dynamic shifts, in the world of existing LED lighting. Wireless controls are becoming more popular in the residential, commercial as well as the outdoor market. New systems are being designed to operate the light sources more interactively and wirelessly. This is where a complete balance of system comes in place for LED lighting as sensors, such as occupancy sensors, timer-controlled sensors, or daylight controlled sensors have found their way in the market.

  While the new-age lighting control system is also looking at integration forming the basket of HVAC that includes Energy Generation, Conservation and Management as a process, the other support functions aim at offering a choice to the consumer through dimming controls or changes in colour output. Many manufacturers have started offering autonomous and semi-autonomous light control systems, that use sensors in the light fixture itself. A key element in the success of these newer systems is the development of low-cost, chip-based sensors, first used in cell phone/ computer display equipment. This improvement in sensing technology would mean that such a system would be able to deliver a preselected setting of dimming and colour temperature as a person enters a particular room.

  Even a building automation paneled with state-of-the-art lighting control can optimise the usage of light in the premises depending on the need, cutting power-bills by at least 30% – especially in institution and hospitality industry.

  Panasonic has also developed a unique index in collaboration with Ritsumeikan University named FEU. It is a Panasonic unique index, yet its theory is based on a science and presented by the Illuminating engineering Institute of Japan. 
Feu is an innovation that turns the focus in lighting design from the conventional ‘illuminance, the amount of light striking a surface, to ‘luminance,’ the human sense of brightness. It does not reject existing design method using illuminance – but optimises lighting design and contributes to further energy saving with a scientific base.

  Such light measurement tools can help one calculate the efficiency of the lighting fixtures.

  One can only hope that the world of LED evolves further, making lives brighter and offering optimum comfort to the end-user, in the age of power-scarcity.

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Yoshiyuki Kato is Director, Lighting, Anchor Electricals Pvt. Ltd.

Source: http://lightingindia.in/blog/post/id/10048/illuminance-to-luminance

Bucherer, Paris

The new store has been almost entirely illuminated with LED. One of the key features of the lighting design was to create an overall lighting atmosphere, which was able to merge all premium brands (presenting themselves within a shop-in shop-system) by establishing a high-value, luxury identity. The lighting design was developed in close collaboration with the interior designers and the client, who benefits since many years from his experience in illuminating watches and jewelry.

  In selected areas, lux levels up to 4000 lx belonged to the briefing. The highly reflective stone flooring was considered positively in the lighting concept, since the radiation on the floor supported the alignment of the shops as well as their various entrances.

  Flush ceiling integrated downlights and wallwashers, precisely co-ordinated with the furniture and product presentations, illuminate the watches and diamonds.

  In order to achieve exact results, different beam angles were obligatory (18O, 24O, 36O, 45O). Suspended ceiling panes with indirect LED-cove lighting systems add elegance and underline the store‘s concept. The colour for all lighting elements was defi ned with 3000OK.

  Lighting objects, hand-made of ceramic blossoms and buds by London artist Valeria Nascimento, were set into “mise-en-scene“ by using narrow-beam LED spotlights. The layouts for all three installations (one for each level) were defined by using 1:1 templates created by the artist, and completed with “light“ by pfarré lighting design. The specialists of Munich‘s Lichtlauf GmbH crafted extraordinary small LED-fixtures for the buds, and, far ceiling-recessed, glare-free downlights individually for this project. In the shop windows, strong adjustable HQI-downlights bring out the sparkle of the products, supported by evenly lit backgrounds using recessed linear LED profi les. Hidden in the base of each window, LED-profi les light up the outer part of the window scene, creating a discreet “passepartout“ effect.

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Credits
Project: Bucherer, Paris Client: Bucherer, Paris
Location: Bvd. des Capucines, Paris
Date of completion: April 2013 Size: 2000 qm/sqm
Architects: Blocher Blocher Partners, Stuttgart Alpha International, Paris
Lighting Design: Pfarré Lighting Design, Muenchen
Art: Valeria Nascimento, London
Photography: Sébastien D’Halloy, Paris, Nikolaus Koliusis, Stuttgart, Arnaud Porcheron, Paris

Gerd Pfarré FIALD is a lighting designer. In 1998, he founded Pfarré Lighting Design, a free lighting design office in Munich. Since 2012, Gerd is the co-editor of the magazine on lighting, ILLUMINATOR.

Source: http://lightingindia.in/blog/post/id/11054/bucherer-paris

A tailored approach to LED Thermal management enhances design while reducing costs

A critical aspect of effective LED –based product designs is ensuring that individual lamps are thermally managed. Although device manufacturers are continuing to improve the durability of LEDs at raised operating temperatures, excess heat in LEDs still has both an immediate impact on performance as well as longer term consequences as can be seen in Fig.1. Short-term, mostly reversible effects include colour shift and reduced light output, while the long-term impact of poor thermal management is accelerated lumen (light output) depreciation meaning a curtailed useful life.

Fig. 1: Impact of temperature on LED life expectancy (Source: Cree)

  As design approaches change and LED technology advances, there is a definite market shift towards the use of mid-power (sub one watt) as opposed to high-power devices (one to three watt) for many LED lighting applications.

  By using a higher number of mid-power devices more closely positioned to one another in an array as opposed to a lesser number of high power devices, a more even light can be achieved. This is especially important in larger designs such as where LEDs arrays are used instead of CFL tubes. This kind of arrangement also simplifies the design, and therefore cost, of the lens/cover fitted over the array as it is not required to mix and spread the light output so much as with ‘point’ light source of a small number of high power devices.

  The approach to thermal design for high-power LEDs is inappropriate and ‘overkill’ for mid-power devices and with careful and early consideration to the design there are opportunities to reduce overall design cost, weight and complexity without impacting performance, reliability and expected life of the lighting assembly in any way.

Thermally managing high-power LED designs

  Despite the growing popularity of mid-power LEDs, higher power devices are still likely to remain the best choice for a significant number of applications until further advances in technology allow even greater lumen per watt output. The power dissipated by high power LEDs is still of course much, much lower than that of other older lighting technologies, however, heat generated in normal operation is concentrated in a much smaller area, base of the individual LED device. By effectively managing the heat in the base, the junction temperature of the diode can be maintained at a level where short-term & long-term performance is not impacted.

  The use of insulated metal circuit boards offers one of the most efficient way of dissipating heat at the required rate and magnitude from designs that utilise high power LEDs. The construction of insulated metal circuit boards comprises a sandwich construction of an aluminium sheet, coated with a very thin electrically insulating dielectric material that possesses a high thermal conductivity. This is then topped with a bonded copper layer that is etched using conventional PCB processes. The LEDs & any other devices required to complete the circuit are then soldered onto the etched copper traces.

  The thin, high thermal efficiency dielectric layer ensures that heat is dissipated to the aluminium baseplate efficiently and effectively. However, in most high power LED designs the thermal performance of the baseplate alone is not enough to provide effective thermal management during the prolonged operating cycles typical in lighting applications. Therefore, the insulated metal circuit assembly must be attached to a larger heatsink or the metal chassis of the equipment or overall product. Using mechanical fixings and a material such as thermal grease tend to provide inconsistent results due to the difficulty in maintaining repeatability of thermal grease application. Also, performance over time may degrade due to the grease flowing from the interface or a relaxing of the closure force of the assembly. A more effective approach that also yields cost savings due to the need for mechanical fixings being alleviated is to use a thermally efficient structural adhesive tape. Materials such as Bondline 200 from Universal Science feature a strong, pressure sensitive adhesive on both sides of a thin foil of aluminium having a thermal conductivity of around 140 W/mK. These types of material exhibit cold flow characteristics when installed between two metals surfaces which means that micro air voids are effectively removed and heat transfer between insulated metal circuit & chassis or heatsink is maximised; this performance is enhanced due to a thin bondline of around 0.16mm which shortens the thermal path between the metallic surfaces. Typically available in rolls in a range of standard widths, or for high volume production, as custom die-cut shapes thermally adhesive tapes allow fast repeatable assembly & deliver long-term, high levels of stable thermal performance.

Taking a different approach for mid-power device-based applications

  Mid-Power LEDs – those rated at around 0.5W to 1.0W dissipate less power and so do not require the high thermal performance of an insulated metal circuit to dissipate heat from their junctions. This presents the designer with an opportunity to reduce the cost and weight of their design by using a standard thin (0.6 – 0.8mm) FR4 printed circuit board material. Mid-power LED lighting product designs can use a format of FR4 that is familiar to designers and PCB fabricators/ processors throughout the electronics industry: that is a thin sheet of glass-reinforced epoxy laminate clad top and bottom with a thin copper foil. During the chemical etching process the copper is selectively removed from the board to leave a finished circuit of copper lands where the individual devices – in this case LEDs and supporting passive components – are mounted, and joined by interconnecting tracks to complete the electrical circuit. On the underside of the board it may be necessary to have some tracks connected to the top side using plated via holes in order to achieve the desired circuit layout. However, to maximise the heat spreading effect, as much copper as possible should be left in place on the underside of the board. In order to promote the optimum heat flow from the individual LEDs mounted on the PCB, the copper pads on which the individual devices are mounted are drilled with multiple vias which are then plated in order to create a small matrix of ‘heat pipes’ to draw the heat from the die of the LED through the PCB to the larger copper area on the underside of the board. If required, the thermal efficiency of this top-to-bottom connection can be enhanced further by ‘flooding’ the via holes with solder.

Photo Credit: Bondline 200 thermal adhesive tape star

Photo Credit: Bondline 700 thermal adhesive tape 

  While mid-power LEDs generate a lot less heat than high-power devices, it is still necessary to attach the FR4 circuit to a more substantial metal surface in order to continually remove the heat and maintain acceptable device operating temperatures. Using a thermal adhesive tape can provide the best approach for achieving this and also removes the need for screws and other mechanical fixings. For the reasons previously described, thermal grease does not provide a consistent, reliable long-term solution and also necessitates the need for screws and other fixings. Modern thermal adhesive tapes such as Universal Science’s Bondline 700 can provide the required combination of adhesion and thermal performance and are specifically designed for bonding FR4 circuits to chassis or other heatspreaders/heatsinks.

  In addition to providing a permanent bond that increases to a maximum level over the first 24 hours after installation, Bondline 700 also flows to fill the micro air voids that can form between the adhesive layer and the underside of the FR4 circuit due to the small ‘steps’ that exist between the copper areas and the FR4 where the copper has been selectively etched away. Other undulations and surface irregularities that need to be filled may also exist on the chassis / heat spreader side of the sandwich assembly. With FR4 the right selection of the interface material and mechanical attachment is much more critical than with MCPCB as can be seen in Fig. 2. Where even higher levels of thermal performance are required Bondline 1800 provides conductivity of 1.8W/mK.

Fig. 2: Image of FR4 using thermal camera

Summary

  With both high power and mid-power LEDs providing options for designers a wide range of commercial and industrial lighting solutions, it is important that the correct decisions are made with regard to thermal management. As well as giving the appropriate degree of heat spreading and dissipation, the right choices can also save money, reduce weight and minimize design complexity.

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James Stratford, CEO of Universal Science Group, got trained as an electro-mechanical design engineer with Her Majesty’s Government Communications. 

Source: http://lightingindia.in/blog/post/id/8449/a-tailored-approach-to-led-thermal-management-enhances-design-while-reducing-costs

EOT Characteristics of LEDs

This makes measuring LED output an important activity but their small size, directionality and narrow spectral emissions that traditional photometric and colorimetric measurement methods are not always the most appropriate. Measurements of major characteristics of a LED that manufacturers and end-users find most important are like total spectral flux, luminous flux, chromaticity, CCT (Correlated Colour Temperature), CRI (Colour Rendering Index), peak wavelength, dominant wavelength, current (I), voltage (V) and luminous efficacy in the field of lighting.

Techniques for measuring EOT

  The lamp measurement system will depend on three things that is measurement needed, physical size of the lamp, and magnitude of the lamp output. Lamp physical dimensions must also be considered. The sphere diameter must accommodate the maximum length of the lamp under test. The CIE recommends that for tubular fluorescent lamps, the sphere diameter should be at least twice the longest dimension of the lamp, and that for compact lamps the sphere diameter should be at least ten times the largest dimension of the lamp. There are different methods and considerations for lamp measurement radiometry and photometry. In general, the measurement of a lamp's luminous flux and its spectral radiant flux are identical except in how the radiation is detected. There are two methods for measuring the total flux of a lamp. The first employs a goniometer that scans the whole sphere of radiation from the source. Integration over this scan yields a very accurate measurement of the lamp output, but the process is not always easy or quick. The second method employs an integrating sphere to capture all the radiation from the source at the same time associated colour parameters are measured. A detector is used to measure the output of the sphere. By comparing the output with a test lamp in the sphere to the output of a known standard in the sphere, the total flux emitted from the lamp can be calculated. This procedure can be done easily and quickly.

Integrating Sphere

  The integrating sphere integrates the total light output of a tested source to produce a single measurement. It is a hollow sphere coated with Barium Sulphate of fundamental optical technology, commonly used in photometry, radiometry, for applications including the test and measurement of light sources (lamps, LEDs), sensors (spectrometers, camera systems), and material properties (reflectance and transmittance). It has become standard instrument in photometry and radiometry. Luminous flux is the total photometric power emitted in all directions from a light source, measured in lumens. With the proliferation of high brightness, LEDs are used for illumination, and measuring the total flux of LEDs has become widespread. The variation in the spatial and angular response of many detector leads to incorrect results when the flux to be measured is non-uniform or the beam shifts slightly. Non-uniformity can originate from the source or optical path. Beam movement can come from moving components or refractive index variation in the air path. Measurements with fiber optics can be influenced by launch or fiber bend conditions. The recorded output pattern changes as the fiber output pattern changes, and light moves across or off a detector.

  The integrating sphere light measurement systems are in sphere sizes ranging from 0.5 meters. The system consist of a spectrometers, source meter, thermal element, DC power supply, Auxiliary lamp (AUX), and calibration lamp (CAL). The integrating sphere must include a lamp socket fixture, baffles, and a viewing port for the photodetector. In high accuracy measurements, an auxiliary lamp may be used to correct for lamp self absorption.

Fig. 1: Integrating Sphere (Courtesy: www.labsphere.com)

  A baffle is placed between the lamp and the detector port. Because the total luminous flux of the lamp is directly proportional to the illumination of the sphere wall, the detector must be baffled from direct illumination by the lamp. The CIE recommendation for the placement of this baffle is that it be 1/4 to 1/6 the sphere diameter from the photometer head. The baffle is coated with the same material as the integrating sphere wall. The most common mounting arrangement places the lamp at the centre of the integrating sphere and the baffle at approximately one-third of the radius from the viewing port.

Measuring procedure

  At first initialization of integration sphere is very important one because to get accurate measurement. For initialization purpose the CAL lamp can be calibrated for accurate total luminous flux and total spectral flux, proceeding with AUX lamp calibration for self-absorption correction. Each lamp screened, seasoned and calibrated then only integrating sphere ready for measurement.

  The LED is placed in the centre of the sphere and connected to the power port. After fixing the LED updating the auxiliary calibration compensates for errors due to size, shape and colour of device under test. Using temperature controller sets the temperature of the LED mounting block. LED power supply panel control the current or voltage to the LED. Then LED total flux is calculated from signals with a standard (known) flux source. But, anything placed in the sphere affects its throughput.

  Fig. 1 shows Integrating spheres measurement setup that collect the total flux emitted from a lamp. Because an integrating sphere reflects and integrates all the light entering the sphere, the light received by a small area of the sphere is directly proportional to the total flux from a light source mounted within the sphere. The total flux from a test lamp is determined by comparing it to a calibrated working standard. Then the instrument produced the output screen, it consists of total spectral flux, total luminous flux graph and parameters, CRI block and CIE chromaticity diagram and parameters.

  TOC analysis is the thermal transient response of the LEDs resulting from a step function excitation carried a large amount of information about the thermal behaviour of the device. The six types of tests that can be performed are:

• ILV @ constant T: Step and control I, wait for T to stabilize, measure L and V 
• VLI @ constant T: Step and control V, wait for T to stabilize, measure L and I 
• TLV @ constant I: Step and control T, wait for T to stabilize, measure L and V 
• TLI @ constant V: Step and control T, wait for T to stabilize, measure L and I 
• ILV/T: Perform an ILV @ constant T, then step T and repeat at each T 
• VLI/T: Perform a VLI @ constant T, then step T and repeat at each T

  Where, L=Lumens, V=Voltage, I=Current,T =Temperature.

Results and Discussion

  The EOT characteristics of LEDs are measured using laboratory Integrating sphere as shown in Fig. 2. The total spectral flux,total luminous flux, CIE-XYZ chromaticity, color rendering index and TOC analysis (case temperature control vs. electrical and optical parameters) of LEDs are measured.

Fig. 2: Laboratory Integrating Sphere

  Spectroradiometry is the techniques of how the energy distributed over visible range & the total flux is the measurement types of light emitted in all directions. Spectroradiometry + Total Flux = Total Spectral Flux (Watts/nm).

  Photometry involves the physical measurement of visible light energy and attempts to compensate for the psychophysical attributes of the human response and physical units of power. Photometry is just like radiometry except that everything is weighted by the spectral response (luminosity function) of the human eye as defined by the CIE. luminosity function as the transfer function of filters which approximate the sensitivity of the human eye. Photometry + Total Flux = Total Luminous Flux (lumens/ nm).

(a) Total spectral flux output

(b) Total luminous flux output 
Fig. 3: Single Green LED with Heatsink

  Spectroradiometry, photometry measurement result of single green LED with heatsink and single yellow LED with heatsink are shown in Fig. 3 and Fig. 4 respectively. Fig. 3(a) and 4(a), total spectral flux waveform x-axis represents visible wavelength range from 360 to 1000 (nm), y-axis represents spectral power (W), this graph indicates spectral parameters in terms of lumens, Kelvin’s, dominant wave, peak wavelength, purity. CIE-XYZ chromaticity diagram x-axis represents the normalized value of X-coordinates, y-axis represents the normalized value of Y-coordinates, this diagram indicates the value of CIEx, CIEy, DUV prime, u prime, v prime and also measure full width half max (FWHM) and center wavelength, centroid wavelength and temperature. Fig. 3(b) and 4(b), Total luminous flux waveform x-axis represents visible wavelength range from 360 to 1000(nm), y-axis represents total flux (lumen/nm). Luminous Flux is the flow of light from a source per unit of time and is measured in Lumens. Then other waveform & measurement parameters are same as that of total spectral flux waveform.

(a) Total spectral flux output

(b) Total luminous flux output
Fig. 4: Single Yellow LED with Heatsink

  From the Figures 3 & 4, it is proved that LED light sources are much more efficient at converting watts to lumens. Different materials can be used within the LED sources themselves, each of which has its own light extraction efficacy. For these and other reasons, Single green LED with heatsink and Single yellow LED with heatsink can consume the same power but differ widely in lumen output. Because power (Watts) can’t be used as an index of light output, evaluating the “brightness” of LED sources.

  In data analysis of redstrip, whitestrip, single LED without heatsink, single green LED with heatsink, single yellow LED with heatsink are display screen in Fig. 5. This LEDs spectral waveform of the total spectral flux (units Watts/nm) over the visible wavelength range from 360 to 1000 (nm).

Fig. 5: Analysis the characteristics of LEDs

  Fig. 5 reveals that lumens of the red strip is high compared than others, because array of led but the value of CCT is very low so it come under warm colour. White strip has lumens is low than LED arrays because is just a module of LED but the value of CCT is very high compared than others so it come under the cool colour. Single LED with heat sink is used to get the same lumens of module LEDs and it has its own power supply ratings. Single LED without heat sink its lumens level is very low. With different colour LED measurement results the lumen is same, the CCT and CRI value of each LED can be varied, so come under different category of quality.

  Table 1 gives EOT parameters of LED, i.e., CIE chromaticity parameters, CCT in Kelvin’s, lumens, wavelength, purity, integration time, temperature, CRI, voltage, current, power. Measures are characterized according to the measurement value, it is useful for customers to identifying the quality of LED and also this measurement is useful for production level industries to improve quality of LED.

• Chromaticity is an objective specification of the quality of a colour regardless of its luminance. The CIE Chromaticity Diagram showing all visible colours. x and y are the normalized amounts of the X and Y primaries present, and hence z = 1 - x - y gives the amount of the Z primary required. These values used for colour matching purpose. 
• The Correlated Colour Temperature (CCT) is a specification of the colour appearance of a light source, relating the colour to a reference source heated to a particular temperature, measured by the thermal unit Kelvin. The measurement can also be described as the warm, cool and neutral of a light source. Generally, sources below 3500K are considered "warm;" while those above 4100K are considered "cool" sources, in between that values are considered neutral. 
• Lumen is a unit of light flow or luminous flux. The lumen rating of a lamp is a measure of the total light output of the lamp. As lamps and fixtures age and become dirty, their lumen output decreases. 
• Dominant wavelength is the spectral colour which can be mixed with white light in order to reproduce the desired colour. 
• Centre wavelength is the average of two wavelengths determined in the 3 dB width of measurements.
• FWHM describes the spectral width of the half power points of the LED. Half Power points are where power spectral density is one half of the peak amplitude. FWHM in the LEDs are classed as high power level or low power level. 
• Purity is defined as the ratio of the distance from the equal energy point E to the color coordinate. All intensity fairly close to the dominant wavelength (spectral colour is 100%). 
• The integration time is the main parameter for the user to adapt the modulation of a spectrometric system to the signal level of the measurement. In many applications it is necessary to have a linear relation between the integration time and the signal, especially in radiometric measurements.

Conclusion

  The electrical, optical and thermal characteristics of various LEDs like18 Volts red LED strip(redstrip), 12 Volts white LED strip (whitestrip), 3 Volts single LED without heatsink, 3 Volts single green LED with heat sink, 3 Volts single yellow LED with heat sink. From the experimental results it is observed that two different LED sources can consume the same power but differ widely in lumen output. The illumination level of LED with heat sink holds good when compared to other LEDs. From the obtained results best lamp can be chosen for particular lighting purpose and also this measurement is useful for production level industries to improve the quality of LED.

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Dr P S Manoharan is working as Associate professor in Thiagarajar College of Engineering, Madurai. N Uma, is pursuing Post-graduate (Control and Instrumentation) in Thiagarajar College of Engineering, Madurai.

Source: http://lightingindia.in/blog/post/id/8478/eot-characteristics-of-leds

Single Molecule Light Bulb

Electric generator stations brought electricity to urban & later rural areas to power them. Later gas discharge lights including fluorescent lights use less electricity to make more light. Energy demand with its rising cost and environmental consciousness have motivated inventors & users to look for green yet environmental friendly lighting products and many First Single-molecule LED people have already changed their house lighting system, from the compact fluorescent lights to the energy-efficient LEDs lights. The LEDs, especially the organic LEDs, are becoming increasingly popular in these days. For information, the organic LEDs are mostly thin films made from organic polymers. It can be easily coated onto large areas at a very low cost. Energy-efficient LEDs are widely tipped to become the predominant lighting source of the next decade and beyond, replacing the fast-disappearing incandescent bulb, as well as the compact fluorescent lights that are replacing them.

  It's like there is not any engineering problem that can not be solved with carbon nanotubes. Now, it turns out it can solve problems we didn’t even anticipate, like making the world’s smallest light bulb. It’s so small, it’s only a few molecules in size. With the going on pace of development in this direction, future light bulb will be one glowing molecule. A single molecule that reliably emits white light and could speed the development of low-energy LEDs has been developed. A single molecule that reliably emits white light could speed the development of low-energy LEDs for the next generation of light sources and displays, say researchers. The nano-bulb consists of a special molecule trapped in the microscopic gap in a carbon nanotube. When current is applied to this molecular circuit, we get light. Scientists have built a molecule, which is able to behave like two separate light-producing molecules. It produces orange and blue light, when it is stimulated with a voltage. The mix of orange and blue light will turn into white. This means, with this technology, it allows the manufacturers to create white emission in much the same way, as creating white light from independent lights. In this case, we’re not only can save much money but it greatly reduces the carbon offset too.

  In recent years, many countries have begun looking to switch from incandescent lighting to compact fluorescent bulbs because the latter are so much more energy efficient. There has also been a lot of interest in using light-emitting diodes (LEDs) for displays and general lighting, again because of the potential energy savings they offer. But with both fluorescent and LED lighting, the quality of white light produced has always left something to be desired. Fluorescent lighting can make people appear unhealthy because less red light is emitted, while most white LEDs on the market today have a bluish quality, making them appear cold. In contrast, OLEDs can be made from a wide range of materials, so achieving good-quality white light is less challenging. It has not been the quality of light that has let OLEDs down but rather their efficiencies. Fluorescent lighting typically operates at around 60 to 70 lumens per watt, while incandescent bulbs operate at about 10 to 17 lumens per watt. In contrast, the best reported power efficiency of an OLED until now was 44 lumens per watt. OLEDs have the potential to grow into a really very energy-efficient light source. One involves reducing its operating voltage by doping the organic material that connects the light-emitting material to its metallic contacts. The efficiency of the device is highly reduced if it is near a metal contact because of a phenomenon called quenching. Another trick was to make the outer surfaces of the device from types of glass that have optical properties that more closely match those of the device substrate. Otherwise, much of the emitted light is reflected and either reabsorbed or lost through heat. The most novel aspect of this new OLED, however, is the organization of different light-emitting materials within the device. Three materials are used–one each for emitting blue, green, and red light–along with a host matrix material in between. Indeed, a major drawback of OLEDs is their longevity. Although companies like Philips are able to make devices with life spans equivalent to fluorescent bulbs–in excess of 10,000 hours–materials that yield higher efficiencies tend not to last so long. 

  Previous attempts using the same basic concept involved linking together two separate molecules into one. But, because energy is able to flow between the two molecular sub-units, one unit typically emits more light than the other, resulting in an unwanted tint. The new molecule does not suffer that problem, and only contains one light-emitting chemical group. When connected to a voltage, this group switches to a high-energy form that emits blue light as it reverts to its original state. Roughly half the time, though, the high-energy form picks up extra oxygen and hydrogen atoms, becoming a short-lived form that produces orange light before reverting to the original state. A large population of the molecules reliably produces equal quantities of orange and blue light that mix to produce an even white. This allows creating white emission in much the same way as creating white light from independent lights.

  Light emitting diodes are components that emit light when an electric current passes through them and only let light through in one direction. LEDs play an important role in everyday life, as light indicators. They also have a promising future in the field of lighting, where they are progressively taking over the market. A major advantage of LEDs is that it is possible to make them very small, so point light sources can be obtained. With this in mind, one final miniaturization hurdle has recently been overcome by researchers as they have produced the first ever single-molecule LED. A single molecule, in contrast, is better measured in nanometers, a unit just a thousandth of the size. Shrinking the light-emitting element of a pixel by the order of hundreds could, then, make for insane, molecular-scale resolution. The device is formed from a single polythiophene wire placed between the tip of a scanning tunneling microscope and a gold surface. It emits light only when the current passes in a certain direction. They observed that the thiophene wire acts as a light emitting diode: light was only emitted when electrons went from the tip of the microscope towards the gold surface. When the polarity was reversed, light emission was negligible. The researchers showed that this light was emitted when a negative charge (an electron) combined with a positive charge (a hole) in the nanowire and transmitted most of its energy to a photon. For every 100,000 electrons injected into the thiophene wire, a photon was emitted. Its wavelength was in the red range. Therefore, the ultimate challenge in the race to miniaturize light emitting diodes (LED) has now been met. From a fundamental viewpoint, this device gives researchers a new tool to probe phenomena that are produced when an electrical conductor emits light and it does so at a scale where quantum physics takes precedence over classical physics. Scientists will also be able to optimize substances to produce more powerful light emissions. Finally, this work is a first step towards making molecule-sized components that combine electronic and optical properties. Similar components could form the basis of a molecular computer. Single molecule light bulb needs an efficiency boost before it can be used in commercial lighting and displays. Currently, the molecule converts electrons into photons at least 30 times less efficiently than commercial LEDs.

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Dr S S Verma is working as Professor in the Department of Physics, Sant Longowal Institute of Engineering and Technology (Deemed university). 

Source: http://lightingindia.in/blog/post/id/8577/single-molecule-light-bulb

Configuring LED pitching for optimal design of Luminairies

The lighting business in India is of the order of Rs 13,000 crores. The present installed electrical capacity in India is 250 GW (as on 30.06.2014) and the annual energy generation is 946 billion kWh/year. Lighting load which is accounting for nearly 18% of the total electrical energy (170 billion kWh/year) and 20% in peak (60 GW) during 1800-2100 hours is presently having virtually no digitally controllable component. There are around 280 million households in India in 2012 of which 190 million are in the rural area and 90 million are in the urban area. Nearly 40% of the rural households use kerosene/lighting systems as they are not connected by the electric grid. A small percentage of electrified households also use kerosene lamps. In the urban area nearly 90% of the households use electric power for lighting. Hence there are still 75 million rural households & 9 million urban households which are dependent on kerosene for lighting.

  The challenges facing the emerging technologies in the Indian context are multiple.

• Covering the total lighting needs of the country including total elimination of kerosene lanterns. 
• Change over from the inefficient lighting systems to energy efficient lighting solutions across the country. The change over requires undertaking energy audits which will provide insight into the viability of retrofits & renovation. 
• Facilitating the technology manufacturing base, adoption and absorption of emerging solutions. 
• Developing focus on balance of systems such as day light solutions, reflectors, luminaries, controls and automation. 

  Emerging technologies are those which are not fully in wide scale use and under the developmental process of improvement. The performance measuring metrics such as EMI-EMC compatibility, electrical quality, starting characteristics and equipment life are not fully developed for these.

  The broad areas of emerging technologies are photonics. Photonics are on the way to take the centre stage both as basic energy converters (solar photovoltaics) (SPV) as well as light sources (LEDs). Flexible electronics based on organic systems is the emerging area in photonics.

  Application wise, the most promising emerging technologies appropriate to the Indian needs are AC LED lamps for indoor, semi-outdoor and outdoor lighting and DC led systems powered by solar photovoltaic for portable lighting systems and off grid systems.

Configurations of LEDs for luminaries

  The LEDs are available as single LEDs and the luminaire configuration is built out of the individual LEDs.

  Table 1 gives typical details of power density and total power of luminaries built out of individual LEDs.

  It can be seen that there is a linear relationship between the power, no of luminaries and the area of cross section. The power is given by 0.14 W/cm2. The number of LEDs is given by 5.5 LEDs/100 cm2 after the initial 5 LEDs. However, these configurations are not the optimal configurations and many of these are based on the ease of placement of the LEDs. For optimal pitching of LEDs to obtain the maximum lumen efficiency, the higher LED density in closer proximity gives better lumen efficiency of the luminarie. Ideally, if all the LEDs are located in close pitch the lumen efficiency of the luminare would increase. However, consideration of heat dissipation would dominate the close pitching which would call for sparse pitching. Also the spread requirement of the application calls for sparse pitching.

Fig. 1: give the variation of power of the luminaire and no of LEDs with area

Fig. 2: give the variation of power of the luminaire and no of LEDs with area

Fig. 3: Circular 

Fig. 4: Circular 

Fig. 5: Circular 

Fig. 6: Circular 

Fig. 7: Circular 

Fig.8: Rectangular

Fig.9: Rectangular

Fig.10: Rectangular

Fig.11: Tube light design

Conclusions

In conclusion, it can be said that-

• Ideally dense pitching of LEDs would give the highest lumen efficiency of the luminaire. However, considerations of heat dissipation and light spread requirements of the particular application would call for sparse pitching. 
• Presently designed pitching of LEDs for various applications are far from optimal and the considerations are mostly the placement of these and the heat dispersion. The pitching is not being optimized from the angle of lumen efficiency of the whole system. R&D studies are called for to optimize the pitching for maximum lumen efficiency.

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M Siddhartha Bhatt is Additional Director and Divisional Head of the Energy Efficiency and Renewable Energy Division of cpri, Bangalore. Neha Adhikari is working as Engineering Officer in Energy Efficiency and Renewable Energy Division, CPRI Bangalore. K Pradeep is working as Engineering Assistant in Energy Conservation and Development Division, CPRI, Bangalore.

Source: http://lightingindia.in/blog/post/id/8612/configuring-led-pitching-for-optimal-design-of-luminairies

Eco Friendly LED & CFL - A Comparative Statement

The problem of harmonics cannot be neglected in cases of installations with high lighting load. This paper presents an analysis of harmonics in a network where lighting is one of the main loads. CFLs and LED lamps with electronic gear are characterized by extremely distorted current, with high total current harmonic distortions. Hence they cause a significant voltage distortion in electrical installations. A comparative analysis is performed on the power quality, maximum loading and economics of CFL lamps and LED lamps.

Greenhouse gases & LED

  The heat generated by conventional electric light bulbs may have been significantly reducing the release of greenhouse gases from natural gas. If all homes switch from (incandescent) bulbs to CFLs, there would be an increase of almost 220,000 tonnes in CO2 emissions in the province, equivalent to the annual emissions from more than 40,000 automobiles. As CFL Contains Mercury, Net mercury emissions for CFL and incandescent lamps is 0.012 mg of mercury per kilowatt-hour and 14% of CFL mercury contents escapes to environment after land fill disposal. CFLs, like all fluorescent lamps, contain mercury as vapor inside the glass tubing. Most CFLs contain 3–5 mg per bulb. As mercury is poisonous, even these small amounts contribute to air and water pollution.

  According to the European Commission Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) in 2008, CFLs may pose an added health risk due to the ultraviolet and blue light emitted. This radiation could aggravate symptoms in people who already suffer skin conditions that make them exceptionally sensitive to light. The light produced by some single-envelope CFLs at distances of less than 20 cm (7.9 in) could lead to ultraviolet exposures approaching the current workplace limit set to protect workers from skin and retinal damage. However, industry sources claim the UV radiation received from CFLs is too small to contribute to skin cancer and the use of double-envelope CFLs "largely or entirely" mitigates any other risks.

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  An LED lamp is a light-emitting diode (LED) product that is assembled into a lamp (or light bulb) for use in lighting fixtures. LED lamps have a lifespan and electrical efficiency that is several times better than incandescent lamps, and significantly better than most fluorescent lamps, with some chips able to emit more than 100 lumens per watt. 

  Like incandescent lamps and unlike most fluorescent lamps (e.g. tubes and compact fluorescent lamps or CFLs), LEDs come to full brightness without need for a warm-up time; the life of fluorescent lighting is also reduced by frequent switching on and off.

  Some governments around the world have passed measures to phase out incandescent light bulbs for general lighting. The aim is to encourage the use and technological development of more energy-efficient lighting alternatives, such as Compact Fluorescent Lamp & LED lamps. Consumers are being encouraged to switch outdated incandescent bulbs to these more energy efficient alternatives. LEDs are more efficient than CFLs but the initial cost is higher so it takes longer to recoup the cost of the bulb. However LEDs last much longer-over 20 years-so they will pay for themselves many times over their lifespan. While an 11w CFL bulb costs $1.25 in bulk, an 8w LED (which produces the same number of lumens as a 40w incandescent bulb) can run anywhere from $10 (available at local hardware stores) to $20.

Environmental impact of LED lamps compared to halogen lamps

• The environmental benefits of using LED lamps to replace Halogen lamps are unquestionable.
• At least 4 times less impact on all environmental impact categories throughout its product life cycle.
• Still significantly lower than that of low voltage halogen lamps even when, extremely high halogen specs are considered.

  The environmental impact calculations are corrected for flux or central beam intensity differences.

  The LED lamp power is doubled and life-time of the LED lamp is reduced by half (sensitivity analysis).

Why Only LEDs

• LEDs are ideal for use in applications that are subject to frequent on-off cycling, unlike fluorescent lamps that burn out more quickly when cycled frequently, or HID lamps that require a long time before restarting.
• LEDs can very easily be dimmed or strobed.
• LEDs light up very quickly. A typical red indicator LED will achieve full brightness in microseconds. 
• LEDs mostly fail by dimming over time, rather than the abrupt burn-out of incandescent bulbs.
• LEDs, being solid state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs which are fragile. 
• LEDs can be very small and are easily populated onto printed circuit boards. 
• LEDs do not contain mercury, unlike CFL.

Basic advantages of LED Light

• Energy efficient - LED’s are now capable of outputting 135 lumens/watt
• Long Lifetime - 50,000 hours or more if properly engineered
• Rugged - LED’s are also called Solid State Lighting (SSL) as they are made of solid material with no filament or tube or bulb to break
• No warm-up period - LED’s light instantly – in nanoseconds 
• Not affected by cold temperatures - LED’s “like” low temperatures and will startup even in subzero weather
• Directional - With LED’s you can direct the light where you want it, thus no light is wasted
• Excellent Color Rendering - LED’s do not wash out colors like other light sources such as fluorescents, making them perfect for displays and retail applications
• Environmentally friendly - LED’s contain no mercury or other hazardous substances
• Controllable - LED’s can be controlled for brightness and color.

Comparison Between Different Light Sources

Energy efficiency

  Energy usage for different types of light bulbs operating at different light outputs. Points lower on the graph correspond to lower energy use Because the eye's sensitivity changes with the wavelength, the output of lamps is commonly measured in lumens, a measure of the power of light as perceived by the human eye. The luminous efficacy of lamps is the number of lumens produced for each watt of electrical power used. The luminous efficacy of a typical CFL is 50–70 lumens per watt (lm/W) and that of a typical incandescent lamp is 10–17 lm/W. Compared to a theoretical 100%-efficient lamp (680 lm/W), CFL lamps have lighting efficiency ranges of 7–10%, versus 1.5–2.5% for incandescent Because of their higher efficacy, CFLs use between one-seventh and one-third of the power of equivalent incandescent lamps. Fifty to seventy percent of the world's total lighting market sales were incandescent in 2010. Replacing all inefficient lighting with CFLs would save 409 terawatt hours (TWh) per year, 2.5% of the world's electricity consumption. In the US, it is estimated that replacing all the incandescent would save 80 TWh yearly. Since CFLs use much less energy than incandescent lamps (ILs), a phase-out of ILs would result in less carbon dioxide (CO2) being emitted into the atmosphere. Exchanging ILs for efficient CFLs on a global scale would achieve annual CO2 reductions of 230 Mt (million tons), more than the combined yearly CO2 emissions of the Netherlands and Portugal.

Conclusion

  LEDs are Competitive, Eco Friendly & Likely to Get Better.Conclusion is that based on eco-friendly, life-cycle assessments and competitiveness, LEDs are about as energy efficient as CFLs as far as their whole life-cycle is concerned. But that seems likely to change, since LED lighting technology is still growing and improving its own performance day-by-day.

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Khule Shridhar Shantaram is Associate Professor and Head of Electrical Engineering Department. Kakad Haridas is undergoing ME Electrical Power System at Matoshri COE and Research, Eklahare, Near Odha, Nashik. Birar Dhanshri P is undergoing Diploma Electrical Engineering at K K Wagh Polytechnic, Chandori, Tal- Niphad, Nashik.

Source: http://lightingindia.in/blog/post/id/8448/eco-friendly-led--cfl-a-comparative-statement