1. LED Basics
Prepared by ISR – University of Coimbra
July 2017

2. LED Basics Content: 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

3. 1. Introduction
Solid-state radiators: are light sources where the light is created inside solid-state materials.
The phenomenon was discovered as early as 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, InGaP/GaAs, GaInAlN/GaN
packaging innovations, improved heat sinking and advanced reflector designs
advances in wafer bonding, and transparent substrates for improved light extraction

4. 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.
LEDs are semiconductor diodes or electronic devices, that permit current to flow in only one direction. The diode is formed by bringing two slightly
different semiconductor materials together to form a PN junction.
In a PN junction, the N side contains negative charge carriers, that is electrons, and the P side contains positive charge carriers, that is electron holes, which indicate the absence of electrons.
When a forward voltage is applied to the PN junction electrons move from the N side towards the P side and holes move from the P side towards the N side and combined (pair electron-hole) in the depletion zone between these regions. Some of these recombination's are radiative in which energy is released in the form of light.

5. 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.

6. 2. How does an LED Work?

7. 2. How does an LED Work? Source:Zeiss
Video only appears in presentation mode!!!
Source:Zeiss

8. 3. White LEDs White LEDs Creating white light White light White light
Phosphors
Color mixing optics
Color mixing optics
Blue or UV LED
Multi-Colored LEDs
Colored and PC LEDs
Figure shows the different ways that white light can be achieved with LEDs.
PHOSPHOR-CONVERTED LED
Phosphors are used to convert blue or near-ultraviolet light from the LED into white light
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

9. 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.
Good-quality white light, which is especially important when it comes to providing good color rendering, is obtained by using a blue LED chip in combination with fluorescent materials that convert much of the blue light into light of different wavelengths spread over almost the whole visible spectrum. In LED technology, such a fluorescent material is called a phosphor: hence the white LED based on this principle is called a “phosphor-converted white LED”.
The Figure shows the spectral power distribution of white phosphor LED, from wwhich it can be seen that now light is emitted over almost the whole of the visible spectrum.

10. 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.
The picture shows the spectral power distributions of tyipical blue, green and red LEDs.

11. 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.

12. 4. LED Packaging LED Packaging SMD LED CoB LED 5mm LED
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 (CoB)
SMD (Surface Mounted Devices),
CoB (Chips on Board) and 5 mm LEDs
SMD LED
CoB LED
5mm LED

13. 4. LED Packaging
Chip-on-board LED technology describes the mounting of a bare LED chip in direct contact with the substrate to produce LED arrays. It provides advantages over traditional surface-mount LED technology in that the packing density of the LEDs is much higher. This contributes to higher intensity, improved uniformity and a more compact package than would be achievable with surface-mount LED technology

14. 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.

15. 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.
Figure shows the projected performance improvement expected for LED products. Focus is on products already considered efficient, but still expecting a doubling in performance by The figure shows the historic and projected performance improvement for LED packages under specific operating conditions. LED packages are the LED light sources used in lamps and luminaires that are already very efficient. Their performance varies significantly with the operating temperature of the LED and the electrical current density.
As of today, LEDs are operating with efficacies of 220 lumens per watt, under favourable conditions. 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).
Source: U4E - 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).

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

17. 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. 

18. 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.
Example: L70 at hours means that after hours, the LEDs are emitting 70% of their original output.
Source: {10] page 22

19. 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 => LED modules for general lighting – Performance Requirements
IEC => Particular requirements for LED luminaires
LM80-08 => Measuring lumen maintenance of LED Light Sources
TM21 => Lumen degradation lifetime estimation method for LED light sources
LM80 is the approved standard for measuring lumen maintenance of an LED package, based on a test period of at least hours;
The TM21 tool takes this data and is used to apply a lifetime projection for an LED luminaire.
LM-80 was developed Illuminating Engineering Society (IES), USA

20. 5. LED Properties Life of an LED - Lumen maintenance
Test results provided by US Standard LM-80 sucha as the L90, L70 and L50 are used by many LED luminaire manufacturers for lumen maintenance thresholds of LED luminaires.
LM-80 Standard requires:
6.000 hours testing ( hours recommended)
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
Additional test conditions to ensure consistent and comparable results.
Leading LED manufacturers test their products to the LM-80 minimum of or hours, and then apply extrapolation methodologies as described in TM-21 to estimate the L90, L70 and L50 figures.
Luminaire manufacturers translate these curves into LED luminaire-specific curves, taking into account the luminaire design.
There are two constraints in translating these test results into LED luminaire performance:
First: catastrophic failures of individual LEDs and other failure modes affect the light output depreciation of a population of LEDs in an LED luminaire. This is not taken into account in LM-80.
Second: there is no validated way to translate the lumen maintenance curve of an individual LED into a curve for the LED luminaire.
Source: [10] page 22

21. 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 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 the threshold value. A B50 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.
Due to the importance of thermal management within LED life, the rate of depreciation will vary from manufacturer to manufacturer and output to output. This data should be sought from the specific manufacturer and is an important value to consider when benchmarking luminaire quality. The B value has no influence within established lighting design maintenance factor calculations.

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

23. 5. LED Properties Life of an LED - Luminaire Life
Luminaire life, on the other hand, has to do with the reliability of the components of an LED luminaire as a system, including the electronics, materials, housing, wiring, connectors, seals, and so on.
Since all the aspects of an LED luminaire are interdependent, operational performance can be determined only by testing the luminaire as an integrated system.
Source: Phillips

24. 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

25. 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

26. 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.

27. 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.

28. 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.

29. 6. The Total Lighting System Luminaires
Light output of LED luminaires with different beam widths
Remember that the light output (lumens) does not tell you the intensity, direction nor how much illumination you will achieve on a surface. It is very easy to achieve high illumination levels on a small area with a narrow beam. This is especially important when comparing the light output of downlights. A 24-degree beam will give an illuminance more than twice that of the same LED with a 36-degree beam.
h -> height
E -> illuminance
d(m) -> distance
Source [10]
Page 18

30. 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.
In a traditional bulb (incandescent, fluorescent metal halide, HPS etc.) a considerable portion of the light output is directed upwards. This light must then be reflected down. The efficacy of the reflector in turn is determined by the quality of finish, operating conditions and ambient temperature. 

31. 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

32. 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.

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

34. 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.
Luminaire efficacy describes the efficacy of the entire luminaire, including the light source, ballast and luminaire losses. The Luminaire Efficacy Rating (LER) provides a metric for comparing the relative energy efficiency of fluorescent luminaires. Initiated in response to the Energy Policy Act of 1992 (USA), LER offers a voluntary rating standard for several categories of commercial and industrial fluorescent luminaires such as 2×4 recessed lensed and louvered luminaires, plastic wraparounds and striplights
𝐿𝐸𝐹= 𝐿𝑂𝑅× ∅ 𝑙𝑎𝑚𝑝𝑠 × η 𝑑𝑟𝑖𝑣𝑒𝑟 𝑃 𝑖𝑛
ηdriver - Efficiency of the ballast or of the LED Driver

35. 6. The Total Lighting System LED + Luminaire Efficacy
Luminaires play a major role
The figure shows an approximate range of efficacy for various common light sources, as of January The black boxes show the efficacy of bare conventional lamps or LED packages, which can vary based on construction, materials, wattage, or other factors. The shaded regions show luminaire efficacy, which considers the entire system, including driver, thermal, and optical losses. Of the light source technologies listed, only LED is expected to make substantial increases in efficacy in the near future.

36. 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
Legislation in Europe, USA, and other parts of the world will effectively ban the use of inefficient incandescent lamps. Most of the replacements will use LEDs. This will either be, as complete new fixtures or as one for one replacements lamps in existing luminaires.
LEDs are also being used to replace linear and compact fluorescente lamps.
Source [10] page 40

37. 7. LED retrofitting LED direct retrofit lamps LED Lamp Types
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
Manufacturers introduce new models several times each year with a commitment of maintaining consistency and offering the most useful, cost-effective LED solutions.
LEDspot PAR distribute light in a precise flood or spot
LEDcandle distribute light in a soft glow or sparkle

38. 7. LED retrofitting
When making such retrofitting several aspects must be taken into account, for instance when replacing a fluorescent T8 lamp by a T8 LED:
Is the new T8 LED lamp suitable for the luminaire that was developed to reflect a specified photometry of a T8 florescent tubular lamp?
Does the new T8 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?
T8 florescent lamp of 36W (1200mm) => 3350 lm (93lm/W)
T8 LED lamp of 16W (1200mm) => 1920 lm (120lm/W)
In conclusion, sometimes it’s better to make a redesign of the lighting system when thinking on making a retrofit to LED lamps;
To maintain the quality of service, sometimes it’s better to use new LED luminaires then making direct retrofit.

39. 7. LED retrofitting
Compared to the flux from the fluorescent tube, the LED retrofit tube typically only emits % with a radiation in a smaller beam angle such as ° 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.
In conclusion, sometimes it’s better to make a redesign of the lighting system when thinking on making a retrofit to LED lamps;
To maintain the quality of service, sometimes it’s better to use new LED luminaires then making direct retrofit.

40. Incandescent Equivalency Average Rated Life (hours)
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
LED bulbs are the most popular type sold in europe and represent major energy saving opportunities. The core of the LED bulb assortments are 6, 10 and 12 watt lamps equivalent to 40, 60 and 75 standard incandescent lamps. They feature light output of 470, 800 and 1100 lumens respectevly, distribute light in all directions. The rated average life based on engineering testing and probability analysis is 25,000 hours for all three lamps
Watts Used
Incandescent Equivalency
Light Output (lumens)
Average Rated Life (hours) 6 40
470
25,000 10 60
800 12 75
1100

41. 7. LED retrofitting Retail or focused task lighting Broad assortment
LEDspot PAR
Retail or focused task lighting
Broad assortment
Dimmable
Cool, light, sleek
45,000 hour rated average life
LEDspot PAR lamps light up retail displays and serve in downlights for focused task lighting or illumination from hire ceilings. There are among the most popular LED lamps today. There are a variaty of PAR lamps available on the market. PAR38, PAR30 and PAR20 lamps with a choice of beam spread, intensity and Kelvin rating.

42. 7. LED retrofitting LED tube Choice of colour with 80-90 CRI
Long life > hours
Choice of integral or external driver
Integral Driver:
Lower wattage
Higher energy savings
Reduced maintenance
Easy retrofit
Built-in driver
External driver:
Higher lumen output
Higher efficiency
Longer life
Nowadays, LED tubes are offering generous illumination, excelent colour and long life. This LED lamps are available in two configurations: integral or external driver. The integral driver offers lower wattage and therefore higher energy savings if the delivered light level is appropriated. Additionally, since the driver is in the lamp, ongoing maintenance is reduced. To instal the lamp, you simply remove the existing balast and rewire the lamp holders to receive input power directly. You should make sure that the wiring confirms to your local electrical standards. The external driver offers higher lumen output, higher efficiency and longer life. With higher output, the external driver configuration can provide effective illumination in more applications. In some countries, this may qualify for energy rebate schemes or tax allowances. It instals like a fluorescent lamp and balast. On like many fluorescent replacements, the LED tube fixtures a diffuser that eliminates the distracting image of the LEDs themselfs. Fluorescent remains among the most cost effective technologies today. LED tube can offer an attractive replacement in several applications. This include cold environments, instalations with frequent switching and applications in which eliminating mercury is a high priority.

43. 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
Decorative candle shaped lamps appear permanently in chandeliers and sconces, which are importante fixtures in hospitality applications, residences, houses of worship, even some formally designed commercial spaces. Some models have clear, refractive optic creates a pleasing source of glowing light in the lamp and it is dimmable. The savings in a chandelier can be very significant given a number of lamps.

44. 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
Popular for accent lighting as well as general lighting. Hallogen spot lamps present both energy and maintenance challenges, which LED replacement can effectivelly resolve.

45. 7. LED retrofitting Choosing the right retrofit lamp
The features to be checked before retrofiting a product:
Lamp Cap and base
Dimming
Transformers compatibility
Physical Dimensions
Before replacing the existing lamps with LEDs you must insure that some factors such as the mechanical and electrical compatibility are correct. There are other characteristics of the lamp that you can make a decision about wich retrofit to choose.

46. 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.

47. 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.

48. 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

49. 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.

50. 8. Advantages and Disadvantages
LEDs high-effiiency of LEDs leads to significant energy savings.
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.
Increased reliability - LEDs fail less often, last longer, emit a more solid, flicker-free, full spectrum light.
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
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.
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.

51. 8. Advantages and Disadvantages
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.
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
LEDs do not contain mercury, unlike compact fluorescent lamps