DOSSIER LED LIGHTING WITH A NEW LIGHT SOURCE

Transcription

1 DOSSIER LED LIGHTING WITH A NEW LIGHT SOURCE Third edition, October 2012

2 Preface LED technology is rapidly changing. Excellent evidence of this is this LED report, which is in its third edition in barely two years time. This document provides objective, technically backed information, which will help you to get a clear understanding of this complex and rapidly changing matter. Are you curious as to the latest developments in the area of OLEDs? Are you in search of information on photobiological safety in LED luminaires? Would you like to know what the points of special interest are in the use of LED tubes? This report will provide you with well-founded answers to your questions. The most recent updates to the document have been identified in the margin. You can always consult the latest version of the LED report on our website at Third edition, October , ETAP NV 2 ETAP Third edition, October Latest version at

3 LIGHTING WITH A NEW LIGHT SOURCE TABLE OF CONTENTS 1. LEDs as a light source How do LEDs work? Types of LEDs The advantages of LEDs LED manufacturers The future of LEDs The next step: OLEDs Designing LED luminaires Options and challenges Suitable light distribution Luminance under control Well thought-out thermal design Binning for constant light quality Electrical safety Publishing the correct data Objective quality information Photobiological safety LED tubes Drivers for LED luminaires Quality criteria for LED drivers Current vs voltage sources Lighting with LEDs photometric aspects Depreciation and maintenance factor Lighting studies with LED luminaires Integration of energy-saving systems Questions and Answers...34 Terminology...35 Third edition, October Latest version at 3 ETAP

4 Section 1: LEDs as a light source 1. HOW DO LEDS WORK? LED stands for Light Emitting Diode. An LED is a semiconductor (diode) emitting light when current flows through it. Semiconductor materials used by LEDs, convert electrical energy into visible electromagnetic radiation, in other words, into light. The stimulus is therefore created by electric current through the diode (more specifically through the junction). The diode through which the electric current flows is unidirectional, as are all diodes: light will only be created if direct current flows through it in the right direction, i.e., from the anode (positive pole) to the cathode (negative pole). Visible Light DC Current flow Anode (+) Cathode (-) Fig. 1: How an LED works The amount of light generated, is nearly proportional to the amount of current flowing through the diode. For lighting purposes current-controlled supplies ( constant current ) are always used (see Section 3). Normalized Luminous Flux Forward Current (ma) Fig. 2: Impact of current on luminous flux The combination of LED (semiconductor), housing and primary optics is referred to as an LED component. This LED component covers and protects the LED, ensures that the heat generated internally is also dissipated and includes a primary optics system, i.e., a small lens, to collect and emit the light generated by the LED in a defined pattern. Primary optics LED Junction Substrate Electrical lead Fig. 3: Composition of an LED component 4 ETAP Third edition, October Latest version at

5 The LED emits monochromatic light. The colour of the light depends on the materials used during production, which can be all saturated colours from the visible spectrum, from violet and blue through green to red. White light can be produced as follows: 1. Bichromatically: - The most prevalent way is to provide a blue LED with luminescent (light-emitting) material, which converts part of the blue light into white (or rather yellow ) light. The composition of said luminescent material determines the resulting light s colour temperature (to read more about colour temperature, see below in this section). 2. Trichromatically: - By blending the colours red, green and blue (RGB). - Through combinations of white LEDs in accordance with the first principle with red or amber-coloured LEDs. In this case various colour temperatures are possible with a single module. 2. TYPES OF LEDS There are many ways to classify LED light sources. At ETAP we distinguish the following types: TYPE 1 - LEDS WITH PRIMARY OPTICS In this case, the lighting manufacturer (ETAP) purchases LED components, tailor-makes PCBs (printed circuit boards) and combines them with secondary optics, which provides the best design flexibility, since the shape of the light module can be fully integrated into the luminaire design. Currenlty only SMD (surface-mounted) LEDs are being used, which are soldered directly onto the surface of a circuit board and benefit from much better heat extraction. These are more recent and are specifically optimised to handle greater loads and luminous flux. Their lifetime and efficiency were considerably improved. In terms of power a full range is available, from Low Power LEDs (from 70 mw to 0.5 W) to Power LEDs (from 1 W to 3 W) and High Wattage LEDs (up to 90 W). The lumenous flux per LED varies from 4 lumen (lm) per component to 6000 lm for the highest capacities. TYPE 2 - PREASSEMBLED PCBS (printed circuit boards) The lighting manufacturer purchases preassembled PCBs from the LED supplier, which are circuit boards on which one or more LEDs are mounted. The necessary operating electronics can also be found on the circuit boards allowing the modules to be easily connected to a power source. Such preassembled PCBs come in various versions (round, linear or strips, flexible substrates, etc.) and can be fitted with Low Power as well as High Power SMD LEDs. Examples include Osram and Philips linear LED PCBs. The preassembled circuit boards have the advantage of being ready-made light modules. On the other hand, the shape of the modules is fixed, which slightly limits freedom of design. Also, the choice of the type of LEDs cannot be fully optimised in function of the intended application. TYPE 3 - LED MODULES (complete lamps) LED modules go one step further: the preassembled PCB is integrated into the required electrical and thermal interfaces in its housing. Secondary optics can also be integrated. Bridgelux module Third edition, October Latest version at 5 ETAP

6 LED modules are the equivalent of the traditional light bulb. The mechanical standardised module is fully characterised by its luminous flux and nominal power, whereby the internal technology is fully shielded. Commercial modules include, among others: LLMs (Linear Light Modules) and DLMs (Downlight Light Modules) Fortimo modules from Philips, which generate white light on the basis of blue LEDs and the so-called remote phosphorous technology. Citizen modules Bridgelux modules Osram PrevaLED (traditional white LEDs). Xicato s spot and washer modules. LED tubes (e.g., Osram, Philips). MAKING THE BEST CHOICE Depending on the application, ETAP selects one of the three types (type 1, 2 or 3). For example, in emergency lighting and Flare products, type 1 components are used since the freedom of choice in LEDs and mounting (specific to type 1 technology) allow for optimal performance in a minimalist design. In other cases, we prefer to make optimal use of the expertise of the LED manufacturer (co-design), of their logistics possibilities (after all, the super-fast evolution of LEDs implies the fast aging of stocks) or of the evolution of their LEDs. In this way, our luminaires can automatically adjust together with manufacturer s LED technology. That is why ETAP also uses type 2 and type 3 LEDs, e.g., for diffusor luminaires or for LED downlights with a classical, secondary reflector. level 1: K7 level 2: Kardó uplight module level 3: D1 with LED 6 ETAP Third edition, October Latest version at

7 UPDATE 3. THE ADVANTAGES OF LEDS ADVANTAGE 1: LONG USEFUL LIFETIME The useful lifetime of LEDs is strongly affected by specific usage conditions, whereby power and internal temperature (and therefore also ambient temperature) are the most important factors. Typically service life of 50,000 hours is assumed. This is understood to mean the time span within which the luminous flux on average drops to 70% of its initial value (see box about MTTF). This lifetime applies provided the LED is used within the postulated temperature limits (typically C). If the correct LEDs and good design are used, these values could be significantly higher (see section 4). Relative lumenoutput (%) ETAP solution with High Power LEDs Typical values High Power LEDs Low Power LEDs Time (h x 1000) Fig. 4: Depreciation of the luminous flux over time Useful LED lifetime A distinction must be made between parametric failure (light output degradation) and catastrophic failure (LED emits no light) in the determination of the LED lifetime. When manufacturers refer to L70 lifetime they mean the time within which a specific percentage of the LEDs decreases to 70% of the original luminous flux. This percentage of the LEDs is shown in B, e.g., B50 indicates 50%. In the determination of this lifetime, however, no account is taken of any potentially failing LEDs, which are removed from the test. A defective LED is nonetheless important to users. When the lifetime is determined with the inclusion of failing LEDs, reference is made to the F lifetime, which will typically be lower than the B lifetime. For example, L70F10 shows the time span within which 10% drops to less than 70% of the original luminous flux or fails for another reason. International standards and recommendations will increasingly promote and even impose the F definition for the lifetime of LEDs Also positive is the fact that LED light sources do not include vulnerable or moving components such as glass, filament or gases. Well-produced LED solutions are therefore quite robust and highly resistant to vibrations or other mechanical stress. Albeit mechanically robust, LED components (as all other electronics components) are nonetheless highly sensitive to electrostatic influences. Touching the LED circuit boards without proper earthing is therefore a fundamental no-no. Direct connection of LEDs to a live supply is to be avoided. Power surges could fully destroy an LED. Halogen 5000 LED = 18x Cree XP-E Q4 350 ma B50/L70 Compact Fluo Compact HID (CDM-T) High-pressure mercury vapour (HID) Lineair Fluo LED hours Fig. 5: Typical values for useful lifetime (simplification) Operating Time (khrs) LED Junction Temperature Tj ( C) Fig. 6: Influence of junction temperature on lifetime Third edition, October Latest version at 7 ETAP

8 Advantage 2: High energy-efficiency possible Cold white LEDs with a colour temperature of 5,000 to 7,000 K (kelvin) these days reach more than 160 lm/w under reference conditions and should be available on the market by LEDs with a lower colour temperature of 2,700 to 4,000 K (most frequently used for lighting solutions in Europe) typically slightly lag behind in terms of efficiency. In these colour temperatures, outputs up to 120 lm/w were available commercially in mid UPDATE Efficacy (lm/w) K 6500 K K9 Lighting (first generation) GUIDE FLARE K9 Lighting (second generation) UM2 LED U7/R7/E These curves are based on the actual perfor mances of LEDs in concrete applications. They can differ from the data published by the manufacturer because of product specific electrical driving and thermal behaviour. Fig. 7: Evolution of the efficacy in LEDs for 2 colour temperatures,with indication of some ETAP products, at junction temperature under normal use (hot lumens) Efficacy: lm/w Here we still refer to lm/w (lumen per Watt) of the lamp (as in traditional fluorescent lighting) under reference conditions (25 C junction temperature Tj for LEDs). In actual user conditions the efficiency achieved in the luminaire will be even lower. To illustrate, an example of R7 and UM2 LED: LED measured in pulse test at 85, comparable to real-life conditions 103 lm/w LED measured in pulse test at 85, comparable to real-life conditions 112 lm/w LED with commercial driver 92 lm/w LED with commercial driver 98 lm/w LED luminaire (including optics and lens) 82 lm/w LED Luminaire (including optical system) 87 lm/w lumen/watt lumen/watt Fig. 8: R7 Fig. 9: UM2 LED For comparison: U5 reflector luminaire with fluorescent lamp 1 x 35W Fluorescent lamp Fluorescent lamp with ballast Luminaire with fluorescent lamp 82 lm/w 87 lm/w 94 lm/w lumen/watt Fig. 10: U5 reflector luminaire 8 ETAP Third edition, October Latest version at

9 LEDs with high colour temperature and therefore colder light have a higher efficiency level than the same LEDs with lower colour temperatures. The luminescent material used to create warm white, contains more red and the efficiency of this red component is lower than that of yellow, which is why the overall efficiency of the LED drops. By way of comparison: LED Metal halide lamps Fluorescent lamps High-pressure mercury vapour lamps Low-voltage halogen incandescent lamps Incandescent lamps Fig. 11: Typical values for efficiency of light sources lumen/w Advantage 3: High-quality colour rendition, choice of colour temperature Colour temperature The colour temperature of a light source for white light is defined as the temperature of a black body of which the emitted light produces the same colour impression as the light source. Colour temperature is expressed in kelvin (K). Bluish light has a higher colour temperature and is experienced as colder than light with a lower colour temperature. There are various subdivisions and designations, each with its reference to recognisable colour temperatures: 10,000 9,000 8,000 7,000 North Light (Blue Sky) Overcast Daylight y Blue Led chip Phosphor 6000K Phosphor 3000K 6,000 5,000 4,000 3,000 2,000 1,000 Noon Daylight, Direct Sun Electronic Flash Bulbs Household Light Bulbs Early Sunrise Tungsten Light Candlelight T c ( K) x Fig. 12: Indication of colour temperatures Fig. 13: Principle of the generation of white light by means of luminescent material For white light in RGB LEDs (in which the colours red, green and blue are mixed) all colour temperatures are possible, but control over time is complex because all three colours have a different temperature dependence. This is therefore applied less often for lighting purposes. In LEDs with conversion by luminescent material the colour temperature is determined by the choice of, on the one hand, the blue of the LED and, on the other hand, the luminescent material. Third edition, October Latest version at 9 ETAP

10 What about emergency lighting? In emergency lighting, ETAP resolutely opts for high colour temperatures. LEDs with high colour temperatures are more efficient and therefore require less battery power. In addition, the human eye is more sensitive to bluish light at low light levels. Colour rendering The CRI or Colour Rendering Index of a light source reflects the quality of the colour rendering of the objects lit by the light source. In order to reach this index, we compare the colour rendering of objects lit by the light source with the colour rendering of the same objects lit by a black reflector (with the same colour temperature). The colour rendering of LEDs is comparable to that of fluorescent lamps and fluctuates, depending on the colour temperature, between 60 and 98. For regular lighting applications in warm white or neutral white, ETAP opts for LEDs with a colour rendering of 80 (according to the NEN-EN standard). For battery-operated emergency lighting systems efficiency is more important than colour rendering (a minimum colour rendering of 40 is required here). That is why we use high-efficiency cold white LEDs in emergency lighting with colour rendering of approximately 60. In white LEDs with conversion by a luminescent material, colour rendering is also determined by the choice of luminescent material (e..g, phosphorous). In RGB colour mixing, the three saturated basic colours are mixed and excellent colour renderings are also possible. Even if in this case, control is more complex. By way of comparison: Fluorescent: Ra between 60 and 98 LEDs: Ra between 60 and 98 Incandescent lamp: Ra of 100 CDM: Ra between 80 and 95 Sodium lamp: Ra of 0 Good to know An LED with a low colour temperature (hence warm white) typically has higher (better) colour rendering than an LED with higher colour temperature (cold white). 10 ETAP Third edition, October Latest version at

11 Advantage 4: Immediate light efficiency when switched on Fluorescent lamps do not immediately emit a full luminous flux when they are turned on. LEDs, on the other hand, react immediately to changes in the power supply. After being switched on they immediately reach maximum luminous flux; they are therefore highly suitable for applications that are often switched on/off and the light is often only turned on for short periods of time. This is also true for lower ambient temperatures, in which they even work better. This advantage is, for example, appreciated in the E1 with LED for deepfreeze applications. In addition, LEDs contrary to CDM lamps, for example can also be switched back on without problems when they are still warm and in most cases, frequent switching has no negative impact on lifetime. Relative lum. flux compared to Tamb = 20 C (%) 140,0 120,0 100,0 80,0 60,0 40,0 20,0 0,0 0:00 0:05 0:10 0:15 0:20 0:25 0:30 0:35 0:40 0:45 0:50 0:55 1:00 Time (h:mm) E1 LED E1 FLUO WITH ADAPTED LAMPS AND BALLASTS SUITED FOR FREEZER ENVIRONMENTS E1 WITH BALLAST SUITED FOR FREEZER ENVIRONMENTS Fig. 14: Comparison of the start-up behaviour of LED vs fluo at -30 Advantage 5: Easily dimmable over a broad range LEDs can be efficiently dimmed over a broad range (from nearly 0% to 100%) or dynamically controlled, which is possible on the basis of standardised dimming methods such as DALI, DMX, 1 10 V or TouchDim. Dimmer losses in LEDs in the lower dim ranges are comparable to dimmer losses in fluorescent lights with the latest dim ballasts. Under full dimming the residual power consumption amounts to 10% of the nominal power consumption. Input Power (W) LED Current (ma) Fig. 15: Effect of dimming on power consumption LEDs are therefore highly suitable for integration into programmed, dynamic environments. Third edition, October Latest version at 11 ETAP

12 There is still a difference in the degree of dimming. LEDs can be highly dimmed, for example to 0.1%*.This is not possible in fluorescent lights; where the dimmability limit in practice is 1 to 3% (depending on ballast and type of lamp). Start-up or stability issues often occur in fluorescent lights under this limit). * This percentage depends on the used driver. Advantage 6: Environmentally friendly From LCA* (Life Cycle Analysis studies, which examine the ecological impact of a product from production to recycling and processing) it appears that LEDs, compared to other light sources, will potentially have the smallest ecological footprint in the future. Furthermore they do not contain mercury, which is the case for fluorescent lamps. * Assessment of Ultra-Efficient Lamps; Navigant Consulting Europe; 5 May Advantage 7: No IR or UV radiation LEDs do not develop ultraviolet (UV) or infrared (IR) radiation in the light beam, which makes them highly suitable for environments where such radiation is to be avoided as in museums, stores with foodstuffs or clothing shops. The LED itself does generate heat, but it is led to the back, away from the object to be lit (we will come back to this later see Section 2.4). 4. LED MANUFACTURERS Currently a limited number of major players with their own production of semiconductors (for white LEDs) are active, e.g., Cree (US), Philips Lumileds (US), Osram (DE), Nichia (JP) and Toyoda Gosei (JP). In addition, a large number of manufacturers purchase semiconductor and luminescent materials and turn them into type 1 or type 2 LED components. Examples include Citizen, Bridgelux, Luminus, GE, Edison, Seoul Semiconductor, Samsung, Panasonic, Toshiba and LG. At ETAP we use a number of criteria to select the manufacturers with which we collaborate. The principal criteria are performance, price, documentation (demonstrable data with reference to valid standards), long-term availability (important for continuity in our production of luminaires). ETAP works with a number of the aforementioned suppliers, depending on the application. 12 ETAP Third edition, October Latest version at

13 5. THE FUTURE OF LEDS LED technology is developing rapidly. The efficacy of LEDs is increasing at a fast pace. These days they are far ahead of halogen and incandescent lamps in terms of light output. Also, when compared to compact fluorescent lamps they are currently highly competitive. In terms of efficiency and/ or specific power some LED luminaires (e.g., U7 or R7 series) now even amply surpass the most efficient fluorescent solutions It is expected that they will soon also be able to compete with the most efficient linear fluorescent solutions. Roughly it can be said that every year the price drops by 10% for the same lumen package or that for the same price you will get 10% more efficacy. Generally, however, a limit of 180 to 200 lm/w is expected for warm colours. New technologies are still being developed to improve efficiency and cost in the long term. Further standardisation initiatives are ongoing in the area of modules, with established lumen packages and well-defined mechanical interfaces (e.g., Zhaga, a consortium for the standardisation of the outside of LED modules, i.e., the interfaces). ETAP is a member of Colour control is ever-improving resulting in closer colour binning (further information on binning can be found in Section 2). 6. THE NEXT STEP: OLEDS UPDATE OLEDs (Organic Light-Emitting Diodes) represent the next step in the development of new light sources that generate light through semiconductors instead of filaments or gas. OLEDs deliver sustainable lighting solutions, which lead to quite a few new application options. OLEDs in various forms OLEDs vs. LEDs The most important difference between LEDs and OLEDs is their structure: OLEDs make use of organic semiconductors. LEDs on the other hand, are made from crystals in inorganic material. They also differ visually. LEDs create twinkling light points, whilst OLEDs are wafer-thin plates that distribute the light evenly over a surface. OLEDs produce a quiet, rather glowing, diffuse and non-blinding light. The compact shape of LEDs lends itself perfectly to the creation of sharp light beams, effects and accents. The thin, flat shape of the OLEDs offers unique options in the area of design and integration, which would not be possible with any other light source. In short, OLEDs will never completely replace LEDs: both are linked to highly specific types of applications, which are for the most part complementary. Third edition, October Latest version at 13 ETAP

14 How do OLEDs work? UPDATE In OLEDs the current flows through one or more wafer-thin organic semiconductor layers, which are wedged between a positive and a negative electrode. The layers are deposited on a glass plate or other transparent material, referred to as substrate. As soon as voltage is applied to the electrodes, current, negative electrons and positive hole current, flow through the OLED. Once these electrons recombine in the active layer, briefly a large quantity of energy is released in the form of light, called exciton. By combining different materials in the organic layers, OLEDs are able to generate light in various colours. OLEDs in the future Visual inspection during production process The current OLEDs are deposited on glass. Currently glass is the only transparent substrate that protects the material on the inside against the impact of moisture and air. However, research is also being conducted on the development of soft plastic substrates, which are able to provide the required protection. This offers prospects for flexible and transformable OLED lighting panels so that each surface, flat or curved, can become a light source, which could lead to the development of lightemitting walls, curtains, ceilings and even furniture. Flexible OLED panels are expected to be available around Currently unlit OLEDs represent a reflective surface that strongly resembles a mirror. Researchers are also studying the development of fully transparent OLEDs, which can even further broaden the area of application. During the day, transparent OLED panels will simply function as windows and light up in the dark. In this way they can be used to mimic natural light or for attractive indoor lighting. During the day they could also be used as screens in homes or offices. The transparent OLED panels are expected to make their way to the market by (source: Philips) OLEDs as an interactive mirror. OLEDs for emergency lighting At the April 2012 Light+Building fair, ETAP for the first time introduced an emergency lighting concept based on OLEDs. During 2013 we will launch a signage luminaire on the basis of OLEDs for emergency lighting. Thanks to their low lighting levels and homogeneous output OLEDs are highly suitable for this application. ETAP emergency lighting concept on the basis of OLEDs. 14 ETAP Third edition, October Latest version at

15 Section 2: Designing LED luminaires 1. OPTIONS AND CHALLENGES LEDs are very small compared to more traditional light sources such as fluorescent lights. In other words, the total light source for a luminaire can be spread over the total surface, which allows for the creation of slimmer luminaires and much more innovative designs. But when designing LED luminaires we are faced with more than one challenge. We must first select the right LEDs for the intended application. Power, luminous output, temperature behaviour, lifetime, colour temperature and cost are important parameters in this respect. The design and integration of optics (lenses, diffusers, reflectors) ensure the desired light distribution. The heat management of LED luminaires is also critical to performance. And we prefer to combine all of this with a beautiful design. Mechanical design Electrical design Optical design Thermal design Cosmetic design New 3D design and production techniques Fig. 16: D4 downlight design Third edition, October Latest version at 15 ETAP

16 2. SUITABLE LIGHT DISTRIBUTION UPDATE Most LEDs have a broad light distribution and emit light at an angle of 80 to 140 (full angle). With the help of secondary and tertiary optics (lenses, diffusers, reflectors or combinations thereof) we are able to achieve a specific light distribution. Suitable light distribution is important in order to keep the specific power and hence also energy consumption in each application as low as possible. a. Refractors or lenses Commercially available lenses Example: Flare spots with highly focused luminance. ETAP-specific lenses Example of lighting: LED+LENS TM series (e.g., R7 with wide-angle lenses). Example of emergency lighting: K9 antipanic, extreme wide-angle lighting b. Reflectors Example: D1 with LED module 16 ETAP Third edition, October Latest version at

17 UPDATE c. Diffusers or light treatment foils Example: UM2 LED with MesoOptics TM Example: R8 LED with diffuser in HaloOptics. d. Light guides Example of lighting: UW Example of emergency lighting: K7 Third edition, October Latest version at 17 ETAP

18 3. LUMINANCE UNDER CONTROL With the constant rise in LED performance and maximum power, source luminance also increases rapidly. This luminance can easily reach 10 to 100 million cd/m². The smaller the surface from which the lights emanates, the greater the light source s luminance can become. A few examples of source luminances: Linear fluorescent - T8 14,000 cd/m² Linear fluorescent - T5 15,000 20,000 cd/m² 17,000 cd/m² (HE) and 20,000-33,000 cd/m² (HO) Compact fluorescent, e.g., 26W 50,000 cd/m² Naked LED 3W (100 lm) 100,000,000 cd/m² Sunlight 1,000,000,000 cd/m² (=10x LED!) A well thought-out optical design is therefore an absolute necessity in order to diffuse the light of these bright point sources, avoid direct exposure and decrease glare. To do so, we are able to use lenses, reflectors as well as diffusers. A few examples: Flare downlights (UGR<19, luminance <1000 cd/m² at 65 ): Diffusion of light source across large surfaces in order to limit luminance. Use of lenses with textured surface for the diffusion of peak luminance per light source. UM2 with LED: the light source is spread over the entire luminaire. The MesoOpticsTM diffusor limits the luminance and allows for controlled light distribution. 4. WELL THOUGHT-OUT THERMAL DESIGN Temperature management (cooling) is without a doubt the greatest point of particular interest in the development of highquality LED lighting. Depending on LED performance 35% of energy is converted into visible light and 65% into heat within the component (dissipation). By way of comparison: fluorescent lights emit some 25% of converted power as visible light. But the difference resides in the fact that in fluorescent lighting some 40% of energy is also emitted in the form of infrared or heat radiation. 35% LIGHT 65% HEAT The luminous output of LEDs drops gradually depending on increasing junction temperature. Published LED luminous fluxes and outputs apply at a junction temperature of 25 C. In practice, actual values will be increasingly lower. In practice, actual light output will be increasingly lower. Recently, hot lumens have been increasingly published, which is the luminous flux at the junction temperature of 85ºC, for example. At lower temperatures, the luminous output increases: LEDs always work better as their operating temperature drops. Luminaire output (lm) led = 18x Cree XP-E Q4 350 ma 100% 98% 96% 94% 92% 90% 88% 86% 84% LED junction temperature ( C) Fig. 17: Influence of junction temperature on luminaire output 18 ETAP Third edition, October Latest version at

19 Temperature not only impacts luminous output. Functional lifetime is also affected whenever a critical temperature is exceeded. Relative Light Output Operating Time (hrs) Fig. 18: Depreciation of the luminous flux over time for different junction temperatures Good temperature management is therefore critical. Heat extraction from the LED to the environment takes place in successive steps (through various heat resistances): The heat generated by the LEDs is led through the substrate to the soldering point (1, internal in LED). From there the heat is spread across the LED circuit board (2). Through a thermal interface (3) for heat transfer between circuit board and heat sink, the heat is spread across the heatsink (4). Through convection and radiation the heat is carried off to the environment. Free flow of air around the luminaire is essential to proper heat emission, which is why the thermal behaviour of an LED appliance will be different for surface-mounted than for recessed luminaires, and for recessed luminaires, sufficient free space around the luminaire must be provided (hence no insulation!). Maintenance of the heatsink (keeping it dustfree) is important as well for a good temperature management. Fig : Thermal design of D1 (left) and D4 (right). Third edition, October Latest version at 19 ETAP

20 5. BINNING FOR CONSTANT LIGHT QUALITY During production, LEDs in the same batch or series display various properties, for example with respect to intensity and colour. The use of a mixture of various LEDs in the same luminaire would therefore inevitably lead to various luminous intensity levels and various light colours, which is why we practise binning. Binning is the sorting of the LEDs according to specific criteria such as: BIN 1 Colour binning: sorting according to colour coordinates (x, y), centred around individual colour temperatures. Flux binning: sorting according to luminous flux, measured in lumen (lm). Voltage binning: sorting according to forward voltage, measured in Volt. y Fig. 21: The principle of binning BIN 3 BIN 2 By selecting a specific colour bin, constant light quality is guaranteed. LEDs in the same bin therefore have the same appearance. Differences in colour bins attract attention when a wall is being uniformly illuminated In the study of colour vision, the so-called Mc Adam ellipse (see figure) is used, which is a region on the CIE diagram, which includes all colours indistinguishable to the average human eye from the colour at the centre of the ellipse. LED manufacturers use SDCM (Standard Deviation Colour Matching), whereby 1 SDCM equals 1 McAdam Fig. 22: Visualisation of McAdam-ellipses (source: Wikipedia) x How does ETAP apply binning? ETAP uses a systematic approach in order to guarantee uniformity at all levels: For each luminaire we always use LEDs with a variation smaller than 2 SDCM. We mark the various assembled circuit boards in accordance with the used colour bin, allowing us to always know from which colour bin the LEDs originate. Within the same partial delivery we always deliver luminaires with the same colour code. For partial deliveries spread over time, this is not guaranteed. Colour deviations may in that case be as high as 7 SDCM. Colour bin Flux bin 20 ETAP Third edition, October Latest version at

21 Fig. 23: Illustration of bins for different colour temperatures (green 2 SDCM; red 7 SDCM) 6. ELECTRICAL SAFETY LEDs work at a low voltage (typically about 3V), therefore it is often thought that electrical safety is not a concern. Currently, lighting solutions with LEDs can run at voltages of 100V or more. As a result, we must take additional measures in order to make the fittings safe to touch. LEDs in series increase voltage LEDs in lighting luminaires are preferably connected in series where possible. The logical result, however, is that the voltage increases. One of the benefits of LEDs is that they run on low voltage with a difference in voltage of approximately 3V per LED. But if 30 LEDs are connected in series within one luminaire, you already have 90V. There are even LED drivers that can generate an output voltage in excess of 200V. These require further protection electrically. Additional insulation needed from 24V International standards (IEC 61347) stipulate that for above 24V*, extra measures should be taken to make the luminaires safe. LEDs and other current conductive parts should not be accessible from the outside. The solution must be found so that the LED can only be touched with special tools after opening. Moreover there must be good basic insulation between all touchable conductive parts of the luminaire and all live parts. In practical terms, ETAP provides sufficient air and maintenance space and uses electrically insulated material without affecting the thermal management. AC DC V< 25 V RMS (I RMS < 0,7 ma) < 60 V DC (I DC < 2 ma) 25 V RMS < V < 60 V RMS < 60 V DC < V < 120 V DC 60 V RMS < V < 120 V RMS Fig. 24: According to the international standards IEC up to 24V (AC) or 60V (DC) there is no risk in touching (green). In LED luminaires with higher output voltage (red) additional safety measures should be taken. *The driver insulation grade determines whether further safety measures are required. Third edition, October Latest version at 21 ETAP

22 7. PUBLISHING THE CORRECT DATA Luminous efficacy is the new criterion For years, the efficiency of fluorescent luminaires has been expressed in terms of percentage, an indication of how efficiently the luminaire uses light. But in the LED era, we refer to lumen per Watt, i.e., light output per unit of power consumption. In this context, it is important that the specific efficiency of the full solution be taken into account, of both light source and luminaire. The efficiency of a fluorescent luminaire is determined by comparing the luminous flux of a luminaire with a naked lamp. An efficiency indication in terms of percentage is highly demonstrable. It shows how efficiently a luminaire deals with a given amount of light. That is why this indication has become the standard for fluorescent solutions. It is also very easy to determine: just measure the luminous flux of a luminaire with lamp and compare it with the luminous flux of the naked lamp. Naked LEDs are no usable reference In solutions with LEDs this is not possible, however, since the luminous flux of a naked LED is no absolute reference. For a start, there are many different types of LEDs, the product is not standardised. Currently there is no usable standard measurement method for the luminous flux of a naked LED. And more importantly, the luminous flux is temperature-sensitive. LEDs perform much better at 25 C than when they have been heated in a luminaire. That is why an indication in terms of percentage would, at the very least, be misleading. Specific luminous efficacy of lamp+luminaire That is why the lighting market is increasingly turning to a different concept. We now no longer look at a luminaire on its own, but at the lamp/luminaire combination. We work with lm/w, based on the amount of energy needed in a luminaire to achieve a certain luminous flux. This might not be as clear as a percentage, but it is more precise. The performance of LED solutions depends on a lot of factors, such as cooling, driver, power density, hot/cold factor (the extent to which the luminous flux declines when temperature rises), etc. The lm/w indication takes this into account: the more favourable these factors, the greater the luminous flux for the same power. At ETAP we constantly aim higher with our LED luminaires. Currently, 80 lm/w can be considered as very low-energy for a luminaire, but as LEDs continue to evolve, the bar will continue to be raised. Fig. 25: On the ETAP product sheets on the website both luminaire luminous flux and specific luminous flux are indicated (website screenshot) 22 ETAP Third edition, October Latest version at

23 In addition to luminous efficacy, further details on LEDs can be found on the ETAP website: Photobiological safety class Colour temperature Power Consumption Type of driver: dimmable or not Power factor Maintenance factor UPDATE 8. OBJECTIVE QUALITY INFORMATION The European lighting industry is currently working on an objective framework for the publication of qualitative performance information concerning LED luminaires. Consumers can only assess claims by manufacturers if they measure and publish quality performance data for LED luminaires in a consistent manner. Claims are not verifiable or comparable Currently in Europe there is no directive or normative framework concerning quality LED-luminaires. Manufacturers do publish quality information, but it cannot be compared with each other. For example: some manufacturers publish good grades for lifetime, but they do not mention how they get to those figures. Or they publish light output and life of the LED-light source, even though those are strongly determined by the optics and design of the luminaire. The lack of uniformity is difficult for consumers, because they often need to compare apples with oranges. European Quality Charter in the making That is why the Federation of National Manufacturers Associations for Luminaires and Electrotechnical Components for Luminaires in the European Union (CELMA) published a Guide on Quality Criteria for LED Luminaire s performance, the so-called Apples & Pears Guide, in which ETAP takes an active part. ETAP has been fighting for a few years now for increased transparency and consistency in the publication of quality claims in LEDs. In the United States and a number of individual (northern) European countries, they are already further along. In recent years ETAP has internally established a private charter, largely inspired by the Scandinavian model. These elements are now also picked up by CELMA. The Lighting Industry Liaison Group has also developed a guide for the specification of luminaires with LEDs (Guidelines for Specification of LED Lighting Products 2011). Indicators for the complete luminaire The CELMA Guide contains guidelines for measuring and publishing performance data and quality features of complete luminaires: - The input power (W) of the luminaire including the power supply, the output luminous flux (lm) and the efficiency = output/input (lm/w) - Display of the light intensity (cd) in a polar diagram - A photometric code that gives an indication of the quality of light (colour temperature of light, colour rendering index, chromaticity and luminous flux) - A maintenance code that indicates the depreciation of light output over time, indicating the expected lifetime, the then remaining flux percentage and the failure rate at that time (see further) - The ambient temperature ( C) for which the published values are valid Does your supplier use a reliable maintenance factor? The above mentioned code for the maintenance factor refers to a verifiable, measurable quality attribute of a luminaire. In practice, that code is usually determined for a period of 6,000 hours, or at best 12,000 hours. But in lighting studies we worked more with depreciations after 25,000 Third edition, October Latest version at 23 ETAP

24 UPDATE (which in many standard applications corresponds to 10 years), 50,000 or 75,000 lighting hours. For this extrapolations must be performed. Since the CELMA-guide does address this, ETAP applies American directive TM21. ETAP extrapolates its data on the basis of this guideline, in order to be able to take the correct maintenance factor into account for each project. Thus customers are assured that their lights perfectly meet the expectations of the planned end-of-life. The service live of the luminaire is for that matter determined by its weakest link, which is not necessarily the LED itself, but can also be the supply, for example. ETAP also takes this into account. generic data LLMF (%) F (lm) P (W) lm/w h h h UM2**/LEDW UM2**/LEDN Fig. 26: For extrapolations ETAP applies the American directive TM21 (e.g. UM2 LED with Lamp Lumen Maintenance Factor) 9. PHOTOBIOLOGICAL SAFETY The European standard for photo biological safety EN describes a measuring method to determine whether a lamp or luminaire carries a risk of eye and skin damage. Given the high luminance resulting from many high power LEDs, there is a risk of eye damage. That is why it is important that the photobiological safety be measured correctly and published clearly. LED light contains almost no light from the ultraviolet or infrared spectrum, and therefore is not dangerous to the skin. It does however provide a high peak in the blue spectrum which, when looking into a bright light source (for a long period of time), may result in irreversible damage to the retina, the so-called the Blue Light Hazard K 80 Relative Radiant Power (%) Wavelength (nm) Fig. 27: Because LED light contains a high peak in the blue spectrum, sufficient attention must be paid to protective measures. 24 ETAP Third edition, October Latest version at

25 UPDATE Four risk groups Whether the risk is real, depends on several factors: capacity of the LED, colour temperature, but also light distribution and distance to the luminaire play an important role. To allow users to estimate the risk, the standard EN determines that lamps and luminaries must be divided into four risk groups. For the Blue Light Hazard, those groups are defined as follows: Risk group 0 ( exempt group): this means that there is no danger, even with unlimited viewing of the light source. Risk group 1: The risk is limited, no more than seconds of viewing is allowed (just under 3 hours). Risk group 2: up to 100 seconds of viewing is allowed. Risk group 3: up to 0.25 seconds of viewing is allowed. This is shorter than the natural aversion reflex of the eye. Safety behind lens or diffusor For light sources of risk group 3, protective measures are always needed. For the other groups, it depends on the application. If the light sources belong in group 2 or 3, then this must be indicated. Normally you do not look into a light for a long time, but a technician must be able to safely monitor the proper operation of the light source. Worst case scenario, the LEDs belong to group 2. In ETAP luminaires that LED is located behind a lens or diffuser, thus levelling off the luminance. The LEDs are behind a diffusor or lenses, which soften the bright LED light. Measure correctly, publish clearly To which group a luminaire belongs is determined according to a specific measurement procedure, using specialized instruments (spectrometer). ETAP has the proper setup and instruments to carry out measurements in-house. This means that ETAP can carefully screen all luminaires for photobiological safety. The solution s eventual risk group will be published on the website and in the product documentation. ETAP has the proper instruments to carry out measurements. Third edition, October Latest version at 25 ETAP

26 UPDATE Fig. 28: You can find exact information about the photo biological safety class of an ETAP luminaire in the product sheet on our website (screenshot website, status August 2012). 10. LEDTUBES LED tubes are ready-made LED lamps that fit into the lamp holders of fluorescent luminaires. ETAP however, issues a warning for some of these solutions: safety is not always guaranteed and quality and comfort are seldom optimal. Unsafe LED tubes prohibited by EU Via the Rapid Alert System, the European Union has blocked sales of various LED tubes (see website of the European Commission because they are not in accordance with the 2006/95/EC Low Voltage Directive and the EN standard for lighting luminaires. In these products there is a risk, among other things, of electric shock during installation as some external components can become electrically charged. Therefore LED tubes are not always reliable or safe. 26 ETAP Third edition, October Latest version at

27 UPDATE Luminaire manufacturer no longer liable Fluorescent lamps cannot be replaced by LED tubes just like that. Often, the wiring needs to be changed, or luminaire components need to be replaced or bridged. This of course means the liability of the original luminaire manufacturer falls due. It is the company s responsibility making the conversion to prove the conformity and issue a CE declaration, which in practice is never done. Over- and underexposure And finally, often the light quality is not very good either. Every luminaire is designed for a certain light output and a certain light distribution. LED tubes change that picture and possibly result in lower lighting levels, worse uniformity, glare, in short loss of comfort. Also the larger loss of light must be taken into account: with LED tubes this can get up to 30% and more at the end of the lifetime of the LED tube. Finally, one should be well informed regarding the desired color and the distribution, since we regularly identify quality problems in this area as well. Fig. 29: While an E12/136HFW (with a 1 x 36W-fluorescent lamp) achieves a luminous flux of 3350 lm, and an efficacy of 72 lm/w, the same device with LED-tube achieves, respectively, only 1340 lm and 61 lm/w. Also, the light distribution with a LED tube (right) is different than the one with fluorescent lamp (middle). When considering LED tubes, you should choose a special luminaire, dimensioned based on an illumination study. Third edition, October Latest version at 27 ETAP

28 Section 3: Drivers for LED luminaires 1. QUALITY CRITERIA FOR DRIVERS The driver is one of the most crucial components in LED solutions, as is now widely recognised. The quality of LED luminaires not only depends on the LED light source and optical design, but also on the efficiency and reliability of the driver. A proper LED driver must meet six requirements: Lifetime. At a minimum, the power supply has to have the same lifetime as the LEDs, which will typically last 50,000 hours (at 70% of the luminous flux). Efficiency. One of the success factors of LEDs is energy efficiency. Therefore the conversion of mains voltage into current must be as efficient as possible. A good LED driver has an efficiency of at least 85%. Power factor. The power factor is a technical indicator of the driver that shows how close the current of the waveform approximates the sinusoidal reference of the voltage. The power factor ( ) is composed of two parts: the shift between voltage and current (cos ) and the distortion of the current (harmonics or the Total Harmonic Distortion). The smaller the shift and distortion of the waveform, the fewer losses and pollution on the distribution network of the energy supplier. For LED drivers, ETAP aims to achieve a power factor in excess of 0.9. Fig. 30: For drivers with a high power factor (left), the waveform of the current (blue) shows little distortion and shifting compared to the voltage (yellow). This is the case, however for supplies with a low power factor (right). Electromagnetic compatibility (EMC). The driver should minimise electromagnetic interference in its surrounding area and, simultaneously, be influenced as little as possible by electromagnetic interference from the surrounding area. Therefore proper electromagnetic compatibility is crucial. Switching current (Inrush current). When an LED driver is put under power there will be a high peak current on the net for a short period of time (a fraction of a millisecond), because at the start condensers are being charged. In drivers with low switching current, the circuit breakers are not deactivated when a number of luminaires are turned on. Waveform current: The good quality of the output current ensures that there are no colour shifts thus preventing flickering or stroboscopic effects. 28 ETAP Third edition, October Latest version at

29 Technical fact sheets Drivers are therefore crucial components in all LED solutions. High-quality drivers can be recognised by requesting the technical fact sheets from the manufacturer to check if the above quality requirements are met. ETAP always provides quality LED drivers, perfectly adapted to the solution and thoroughly tested in our labs. ETAP testing labs 2. CURRENT VS VOLTAGE SOURCES LEDs are current-controlled components. The current is directly responsible for the luminous output and must therefore be carefully adjusted. Two control methods are used: Constant current sources Directly convert mains voltage into constant current. This method yields the highest efficiency and is the most cost-effective method. The disadvantage is that modules with a constant current source can only be connected in series, which is more difficult in terms of installation. In addition, for higher levels the required output voltage adds up quickly (>100 V). Examples: Flare spot 500 ma, DIPP4, etc. Flare D4 downlight constant current 230 V AC LED driver Constant voltage sources Power supplies that convert mains voltage into carefully controlled voltage. When they are used with LEDs or LED modules, these supplies must always be fitted with a current limiter (e.g., a resistance) or a DC LED driver that converts direct voltage into constant current. The major advantage of voltage sources is that several modules can be easily connected in parallel. Examples: LED strip with 24 V supply (limitation by series resistances) Flare spot 24 V (DC LED driver integrated in the cable) constant current DC LED driver 230 V AC power supply Codes for luminaires for constant current sources end in C (for current ); codes for luminaires for constant voltage sources end in V (for voltage ). Third edition, October Latest version at 29 ETAP

30 Also for dimmable luminaires The driver should not only be reliable and efficient, it must also have the flexibility to be used in any modern lighting installation. In many cases the level of lighting must be adjustable, for example through a light control system such as ELS or an external dimmer. Note: it is important that the efficiency and the power factor remain the same when using a dimmer. UPDATE The maximum achievable efficiency for a driver is determined by the nominal power for which the driver was designed (see Figure 31). For drivers with a nominal power <25W maximum efficiency will never be higher than 80-85%. For drivers with a power greater than approx. 35W maximum efficiencies of 90% and higher can be achieved. Efficiency driver 1,00 0,90 0,80 0,70 0,60 0,50 0,40 0,30 25W 75W 0,20 0,10 0,00 0% 50% 100% Driver stress as % of nominal current Fig. 31: Impact of driver stress on efficiency, for a low power driver (blue) and high power driver (yellow) The above graphic shows that the actual efficiency of a driver also depends on the load. For a quality driver the efficiency will remain fairly constant to a minimum load of 50-60%. For lower loads the efficiency decreases significantly. That is why it is important to gear LED module and driver to each other, so that the driver always runs in its optimal operating range. All known dimming systems can in theory also be applied to LED lighting: DALI 1-10V (applied less frequently in LED lighting) TouchDim DMX (applied less often to lighting, primarily used in the theatre) 30 ETAP Third edition, October Latest version at

31 Section 4: Lighting with LEDs photometric aspects 1. DEPRECIATION AND MAINTENANCE FACTOR A lamp s luminous output decreases over time, which is referred to as depreciation. In order to take into account this loss, a maintenance factor is used in lighting studies (a number between 0 and 1), in order for the illuminence not to drop below a certain level over time. On the one hand, when used correctly, LEDs will from an electrical point of view work for a very long time. On the other hand, the LEDs luminous flux will decrease (depreciate) over this long lifetime. Both temperature management and electrical control have a major impact on this drop. The drop in luminous flux is primarily the result of the fading of the internal reflector and substrate, and of the decreased efficiency of the phosphorus that converts the light. Relative lumen output (%) Time (h x 1000) Fig. 32: Depreciation of the luminous flux over time Depreciation in fluorescent lighting In lighting studies with fluorescent luminaires, these days, we often use a total depreciation (drop in luminous flux) of 15%, of which approximately 10% is due to lamp aging. 15% depreciation corresponds to a 0.85 maintenance factor. Maintenance factor (MF) Dust pollution levels minimum low medium high Open luminaires for direct lighting (T5 - Ø16 mm of T8 - Ø26 mm: Ra > 85) Group replacement 0,85 0,80 0,75 0,70 Replace broken lamp + group replacement 0,90 0,85 0,80 0,70 Correction factor for Luminaires with cover for direct lighting Luminaires with painted reflector MF x 0,95 MF x 0,90 Fig. 33: Typical maintenance factors used with fluorescent lighting Depreciation in LED lighting The lifetime claimed today for LEDs involves an average light loss of 30%, which impacts the way we deal with depreciation factors for LEDs in lighting studies. Under normal circumstances, ETAP always follows the market standard; the problem is that currently there is no market standard for LEDs, which is why we use the maintenance factors corresponding to a lifetime of approximately 25,000 hours (+/- 10 years under normal conditions). In addition, we have an overview table to work with adjusted lifetimes (see point 2, Lighting studies with LED luminaires ). Third edition, October Latest version at 31 ETAP

32 2. LIGHTING STUDIES WITH LED LUMINAIRES UPDATE When drawing up lighting studies, we furthermore take into account Assumed service life (25,000, 50,000 or 75,000 burning hours) the LED used (LLMF or Lamp Lumen Maintenance Factor) Application (office or industry) Lamp survival factor Room pollution (room maintenance factor) Soiling of optics (open or closed luminaire) An example: In a lighting study with U7 in an office environment, the maintenance factor is calculated as follows: 99% (lamp maintenance factor) x 1 (lamp failure in LED luminaires is nearly non-existent, and therefore has no influence) x 0.94 (soiling of room) x 0.95 (maintenance factor for closed luminaire) = 88%. This means that after 25,000 hours, 88% of the luminous flux remains. After 50,000 87% of the luminous flux remains, which is significantly higher than the standard 70% after 50,000 (see box on page 7). After 75,000 hours, U7 still has 86% of its initial luminous flux. LED type LED luminaires 25kh 50kh 75kh LLMF (%) Clean office Industry Clean office Industry Clean office Industry 25kh 50kh 75kh High Power U Fig. 34: Extract from table with maintenance factors and LLMF of U7 for 25,000, 50,000 and 75,000 burning hours (status mid-2012) 3. INTEGRATION OF ENERGY-SAVING SYSTEMS LEDs are not only an energy-efficient light source, they also work perfectly with light control systems. This combination allows for a high savings potential, but also creates a few further advantages: LEDs can be dimmed more efficiently than fluorescent lamps and their service life is not shortened by frequent switching. The best known light control systems are motion detection, which dim or switch on the light when users enter or leave a space, and daylight control, whereby the light is dimmed depending on the amount of daylight entering a space. A combination of both systems can save 55% or more energy in specific situations. Currently one in six luminaires marketed by ETAP, is fitted with individual daylight control. LEDs are less sensitive to switching LEDs have a number of specific features that make them D4 downlight with daylight dependent light control (ELS) particularly suitable for use with light control systems. For example, frequent switching has little impact on the LEDs service life. This in contrast to fluorescent lamps, which when switched on each time lose a small part of the emitter material in the lamp. This can be seen, for example, in the ends darkening in the lamp. In spaces with relatively short presences just think of sanitary facilities or corridors we see that the replacement frequency for fluorescent lamps quickly adds up. LEDs do not have that problem. Since an LED is an electronic component, which is impervious to frequent switching. In addition, LEDs instantly provide full luminous flux when switched on, which increases user comfort when entering the space. 32 ETAP Third edition, October Latest version at

33 UPDATE LEDs react faster Electronic switching has a second advantage. LEDs not only respond quickly when switched on, but also react to any change in the supply, which also means that they can be more easily and precisely dimmed. Fluorescent lamps react more slowly, especially when cold. R7 with movement-dependant light control Third edition, October Latest version at 33 ETAP