LED Basics Prepared by ISR University of Coimbra

LED Basics Prepared by ISR – University of Coimbra July 2017

LED Basics Content: 1. 2. 3. 4. 5. 6. 7. 8. Introduction How does an LED work? White LEDs LED Packaging LEDs Properties The Total Lighting System (Drivers, Luminaires) Retrofiting Lamps Benefits and disadvantages of LEDs 2

1. Introduction Solid-state radiators: are light sources where the light is created inside solid-state materials. • • The phenomenon was discovered as early as 1907. The first practical product based on it was developed in 1962. Although LEDs are a relatively old technology they have witnessed a dramatic leap in the 1990's due to: • • • new semiconductor materials developed in the search for red, green and blue lasers, In. Ga. P/Ga. As, Ga. In. Al. N/Ga. N packaging innovations, improved heat sinking and advanced reflector designs advances in wafer bonding, and transparent substrates for improved light extraction 3

2. How does an LED Work? • LEDs are semiconductor diodes, that permit the current to flow in only one direction. • The semiconductor material is layered as a p-n junction. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. Hence the name Light- Emitting Diode or LED. • All diodes can emit electromagnetic radiation. The semiconductor materials used in LEDs are selected so as to emit in the visible range. • Different materials produce light with different wavelengths and thus different colors. 4

2. How does an LED Work? • The n-material has an excess of electrons (which are free electrons), whereas the p-material has electrons missing i. e. electron holes. • Applying a voltage across the p-n junction moves electrons towards the junction of the two materials. • Electrons from the n-material fall into the holes of the p-material. In doing so, the electron moves from a high energy level to a lower one, and the energy difference is emitted as light or heat. 5

2. How does an LED Work? 6

2. How does an LED Work? Source: Zeiss 7

3. White LEDs Creating white light White light Phosphors Blue or UV LED PHOSPHOR-CONVERTED LED Phosphors are used to convert blue or near-ultraviolet light from the LED into white light White light Color mixing optics Multi-Colored LEDs Colored and PC LEDs COLOR-MIXED LED Mixing the proper amount of light from red, green, and blue LEDs yields white light HYBRID METHOD LED A hybrid approach uses both phosphor-converted and discrete monochromatic LEDs 8

3. White LEDs Phosphor-Converted Led (PC-LED) • • For most applications, the white light from the LEDs is produced from a blue chip. This chip also produces shorter (invisible) wavelengths which stimulate a phosphor coating to produce white light. The yellow patch when the LED is switched off is the phosphor coating. 9

3. White LEDs Red, Green and Blue LEDs • • • One way to produce white light is to combine RGB chips together in a single point. This may not produce good results since, over time, the colors degrade at different speeds and so the white appearance becomes colored. LEDs are more efficient at producing colored light because there are no losses due to filtering white light. By carefully controlling the output of each Red, Green, Blue (RGB) chip, almost any color can be achieved including Warm and Cool white. 10

3. White LEDs Tuneable White LEDs In a manner similar to the way that light intensity can be varied by dimming, Tuneable White enables infinite adjustment of the light temperature. From "warm white" to "cool" daylight, light-colour ranging between 1, 700 K and 6, 500 K are possible. State-of-the-art drivers and light control devices make it possible to precisely adjust light temperatures to suit the given circumstances, not only in retail and office environments, but also in medical facilities and other applications. 11

4. LED Packaging Ø LED chips can be implemented into various form factors via a number of packaging methods: • 5 mm LEDs • Surface Mounted Devices (SMD) • Chips on Board (Co. B) SMD LED Co. B LED 5 mm LED 12

4. LED Packaging 13

5. LED Properties Efficiency • Energy that is not released as radiated light is converted into heat and is lost. This is the internal efficiency of the LED. • Some of the light is lost within the semiconductor material due to effects such as total internal reflection, absorption, and shadowing of contacts etc. . , resulting in only a certain portion of the light exiting the package. This is the extraction efficiency of the LED. • The overall efficiency of an LED package is the combination of both the internal and extraction efficiency of the LED. 14

5. LED Properties Efficacy LEDs are highly energy efficient when measuring light output for watts of electricity input. In the market today, the most efficacious LED lamps operate at around 150 lumens per watt. Source: U 4 E - Energy-Efficient Lighting The grey-shaded bars show the potential for further improvement with phosphor-converted blue or violet LEDs (PC-LED), hybrid mixtures containing additional red emitters (HY-LED) and with four or more primary emitters covering the whole spectrum (RGBA CM-LED). 15

5. LED Properties Efficacy – Available in the market (Mid-2017) Incandescent Halogen White LED Mercury vapor Linear Compact Fluorescent High pressure sodium Metal Halide 16

5. LED Properties Efficacy Ways to improve the LED efficacy: • Advances in material sciences to create materials with better band gaps • Better fabrication techniques for reducing the cost and increasing the efficiency • Improvement in heat dissipation • Light extraction from the material comprising the diode. New materials allow more light to be extracted, thus, improving the lumen per watt characteristics of LEDs. • Improvements in phosphor technology to increase the efficiency of conversion of light from one wavelength to a wider band of wavelengths. 17

5. LED Properties The life of an LED • Contrary to most conventional lamps, in well designed fixtures(contrary to conventional lamps), LEDs do not fail abruptly or catastrophically. Instead, their light output deteriorates over time. • Lifetime is therefore based on the lamp lumen maintenance factor (LMF). This is the amount of light from the light source at a specific time in the future. • Life is referred to as Lxx where “xx” is the percentage of light output remaining after a certain number of hours. Ø Example: L 70 at 60. 000 hours means that after 60. 000 hours, the LEDs are emitting 70% of their original output. 18

5. LED Properties Lifetime of an LED • With the advent of LED luminaires, different standards and terminology from conventional source lamps are being used to define life; • • IEC 62717 => LED modules for general lighting – Performance Requirements IEC 62722 -2 -1 => Particular requirements for LED luminaires LM 80 -08 => Measuring lumen maintenance of LED Light Sources TM 21 => Lumen degradation lifetime estimation method for LED light sources • LM 80 is the approved standard for measuring lumen maintenance of an LED package, based on a test period of at least 6. 000 hours; • The TM 21 tool takes this data and is used to apply a lifetime projection for an LED luminaire. 19

5. LED Properties Life of an LED - Lumen maintenance • • Test results provided by US Standard LM-80 sucha as the L 90, L 70 and L 50 are used by many LED luminaire manufacturers for lumen maintenance thresholds of LED luminaires. LM-80 Standard requires: Ø 6. 000 hours testing (10. 000 hours recommended) Ø Testing at three surface temperatures: 55°C, 85 °C and a third one determined by the manufacturer, to see the effects of temperature on light output Ø Additional test conditions to ensure consistent and comparable results. • • Leading LED manufacturers test their products to the LM-80 minimum of 6. 000 or 10. 000 hours, and then apply extrapolation methodologies as described in TM-21 to estimate the L 90, L 70 and L 50 figures. Luminaire manufacturers translate these curves into LED luminaire-specific curves, taking into account the luminaire design. 20

5. LED Properties Life of an LED – L and B value • The L value states the percentage of initial lumens that will be delivered by an LED luminaire at a point in time; • For example, an LED luminaire that is stated as having a lifetime metric of L 90@50, 000 hours will be delivering 90% of the initial lumen output at 50, 000 hours; • The lumen output of LED chips will depreciate at slightly different rates. The B value defines the % of LED chips that will fall below the L value threshold; • The remaining chips will be at or above threshold value. A B 50 value stated provides the median performance of a light fixture with 50% of the chips being below the lumen output (L value) and the remaining being at or above. 21

5. LED Properties Life of an LED – L and B value 22

5. LED Properties Life of an LED - Luminaire Life Source: Phillips 23

6. The Total Lighting System The efficacy of the total lighting system is affected by: 1) Driver efficiency 2) Luminaire / System efficiency 3) Lumen Maintenance driver/ballast light source luminaire 24

6. The Total Lighting System Drivers Fluorescent and high-intensity discharge (HID) light sources cannot function without a ballast, which provides a starting voltage and limits electrical current to the lamp. Similarly, LEDs require a power supply (commonly called a “driver”). The power supply converts line (AC) power to the appropriate DC voltage and current 25

6. The Total Lighting System Drivers • Unlike a transformer, which supplies a constant output voltage (current varies with the electrical load), the driver maintains a constant current through the LEDs and it is the driver output voltage that varies. • The driver also protects the LEDs from normal supply voltage fluctuations and occasional voltage‘spikes’. • Drivers can be integrated in the lamp, located inside the luminaire, as a separate component to the luminaire, or some distance away. • Drivers can be used for color changing (in this case, they have three output terminals for RGB LEDs), dimming and control. 26

6. The Total Lighting System Drivers Driver Efficiency • High quality devices feature efficiency upwards of 85% (η ≥ 0. 85). • Also important is the standby power consumption of the driver!! • High power factor and low harmonic distortion is also desirable. 27

6. The Total Lighting System Luminaires A number of parameters are relevant to select the appropriate luminaire for your application: • The appearance • The light distribution needed • Is there a need for a combination of direct and indirect lighting? • Is there a need for directing the light by reflectors? • Glare control, the needed light distribution and illuminance (lux) and being as energy efficient as possible. • Is there a need for lighting control and which types of controls are needed? • Ease of maintenance including resistance to dirt, cleaning, exchange of components, modular design and repair. 28

6. The Total Lighting System Luminaires Light output of LED luminaires with different beam widths 29

6. The Total Lighting System Luminaires Light output of an LED (luminaires) Trapped light and reflection inefficiency are the first source of lower light output from traditional lamps. 30

6. The Total Lighting System Luminaires Temperature and Light output of an LED • • • The light output from an LED is affected by temperature, reducing as the chip temperature rises. The difference in light output between a chip running at 25°C and 125°C may be as much as 50%. Reducing the LED operating temperature, also increases its life-time 31

6. The Total Lighting System Luminaires Light output of an LED (luminaires) • One of the most important aspects of achieving high light output from an LED is to make sure it is fitted in a well-designed luminaire. Must be designed so that it quickly and easily conducts the heat away from the LEDs • Fitting aluminium fins on the rear of the luminaire; For high power lamps: • Using small fans fitted to blow air across the fins; • Using liquid cooling, similar to that used in cars radiators. 32

6. The Total Lighting System Luminaires Light output of an LED (luminaires) Example of cooling fins 33

6. The Total Lighting System Luminaires Luminaire efficacy factor (LEF), also known as luminaire efficacy ratio, measures the lumen output of a fixture as a function of input power, enabling comparisons between fixtures. The higher the LEF, the more efficient the luminaire. 34

6. The Total Lighting System LED + Luminaire Efficacy Luminaires play a major role 35

7. LED retrofitting LED retrofit lamps • Retrofiting lamps into existing luminaires is a quick and easy way to save energy. • It is quite often possible to improve the quality of the light. • Payback period often less than two years 36

7. LED retrofitting LEDspot distribute light in a precise flood or spot LED direct retrofit lamps LEDcapsules emit an intense Bright light in all directions LEDbulb distribute light in all directions LED Lamp Types LEDtube distribute light in a soft wash LEDspot PAR distribute light in a precise flood or spot LEDcandle distribute light in a soft glow or sparkle 37

7. LED retrofitting When making such retrofitting several aspects must be taken into account, for instance when replacing a fluorescent T 8 lamp by a T 8 LED: • Is the new T 8 LED lamp suitable for the luminaire that was developed to reflect a specified photometry of a T 8 florescent tubular lamp? • Does the new T 8 LED have good heat dissipation? • Will the beam angle of the LED lamp affect the uniformity of the light in the room? • How many lumens does it have? Is it necessary to install more luminaires to deliver the same lumens as before? • • T 8 florescent lamp of 36 W (1200 mm) => 3350 lm (93 lm/W) T 8 LED lamp of 16 W (1200 mm) => 1920 lm (120 lm/W) 38

7. LED retrofitting • Compared to the flux from the fluorescent tube, the LED retrofit tube typically only emits 50 - 60% with a radiation in a smaller beam angle such as 135 -160° where the fluorescent tube radiates in 360°. • Depending on the luminaire, the installation geometry and the application, the smaller beam angle of the LED tube typically compensates for the smaller flux direct under the luminaire with provision of the required amount of lighting. But the original light calculation is no longer applicable as the luminaire geometry and reflector is only providing optimal light distribution and reflectance in the room when the fluorescent tube is used. • The LED retrofit solution might not be acceptable as the client might experience black spots in the room with too little lighting. 39

7. LED retrofitting LED bulbs • • • LED bulbs are the most popular type sold in Europe and present major energy saving opportunities. Their long life and energy saving makes them a very attractive proposition to both domestic and comercial customers. These are mainly used in lampshades, table lamps and free-standing luminaires. Both dimming and non-dimming LED retrofits are availabe Source: Reggs Watts Used Incandescent Equivalency Light Output (lumens) Average Rated Life (hours) 6 40 470 25, 000 10 60 800 25, 000 12 75 1100 25, 000 40

7. LED retrofitting LEDspot PAR • • • Retail or focused task lighting Broad assortment Dimmable Cool, light, sleek 45, 000 hour rated average life 41

7. LED retrofitting LED tube • • Choice of colour with 80 -90 CRI Long life > 25 000 hours Choice of integral or external driver Integral Driver: Ø Lower wattage Ø Higher energy savings Ø Reduced maintenance Easy retrofit Built-in driver External driver: Ø Higher lumen output Ø Higher efficiency Ø Longer life 42

7. LED retrofitting LED candle • • Decorative lighting Elegant candle design Warm colour Clear, refractive optic Dimmable >80% energy savings. 25, 000 hour rated average life time 43

7. LED retrofitting LEDspot • • • Accent and ambient lighting Solves both energy and maintenance challenges of an Halogen spot lamp High beam spread rate Operates on electronic driver or magnetic transformer The bi-pin lamp can fixtures a dimmable driver 25, 000 hours rated average life 44

7. LED retrofitting Choosing the right retrofit lamp The features to be checked before retrofiting a product: Ø Ø Lamp Cap and base Dimming Transformers compatibility Physical Dimensions 45

7. LED retrofitting Lamp Cap and base • • Smaller wattage lamps are available with a range of different caps and bases. The pin can be a different diameter or distance apart. Similarly, screw bases are available in different diameters. 46

7. LED retrofitting Driver / Dimming • • • Some brands of LED electronic driver technology are not compatible with each other. Dimmer compatibility is of high importance as many LED products are often not completely compatible with currently installed dimmers. As manufacturers are still trying to define and adopt a new dimming standard, the dimmer compatibility of LED products is likely to continue to be a problem. Some dimmable LEDs are physically larger than non-dimming ones. If the existing installation does not have a dimmable system, it may be worthwhile installing dimming lamps so that the client can introduce a dimming system at a later date and save additional energy. Some LED retrofit lamps will work on almost all dimmers, but others will only on some. You should always check compatibility with the dimming system before installing retrofit lamps. Check whether that the LED can dim to a low level since some will start to flicker around below 30% output. 47

7. LED retrofitting Physical Dimensions • • • Although the lamp cap might be correct, not all retrofit lamps are the same physical size. It is necessary to make sure that the retrofit lamp will actually fit inside the light fitting. In recessed downlights, it’s necessary to check that the lamp support mechanism accepts the retrofit 48

8. Advantages and Disadvantages • Higher initial cost. LED bulbs are currently priced at the high end of affordability in home lighting markets. The growing widespread use of LED light bulbs in homes and offices, is quickly driving down prices. • Thermal management. LEDs require very efficient thermal management and heat sinking without which the junction temperature of the LED will rise, eventually leading to premature failure. • Color maintenance. LED’s can shift color due to age and temperature. • Heavy compared to CFLs and incandescent lamps. Some LED bulbs incorporate an integrated metal heat sink. This makes them heavier than similarly sized filament and CFL lamps. The added weight may require sturdier luminaires when retrofitting. 49

8. Advantages and Disadvantages Advantages ü LEDs high-effiiency of LEDs leads to significant energy savings. ü Lower Lifecycle Cost – Despite the higher initial cost, when considering the total cost of ownership (including energy and maintenance costs), LEDs far surpass conventional technologies. ü Increased reliability - LEDs fail less often, last longer, emit a more solid, flicker-free, full spectrum light. ü 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. ü LEDs can very easily be dimmed ü Since more of the energy drawn is converted into visible light, less is converted into wasteful heat. This can lower air-conditioning costs in establishments and homes that replace many incandescent and CFL bulbs with LED units. ü Silent operation - LED lamps demonstrate virtually noise free lighting. Even when fed from a light dimmer, buzzing, ringing, or whistling of any kind is virtually unheard of. 50

8. Advantages and Disadvantages Advantages ü Wide range of color temperatures - Unlike incandescent bulbs, LED lamps are available in several color temperatures, and in some models the colors can even be controlled. ü 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 ü LEDs do not contain mercury, unlike compact fluorescent lamps 51