LEDs are light emitting diodes. These are electronic components that convert electrical energy directly into light through the movement of electrons within the material of the diode. LEDs are important because owing to their efficiency and low energy, they are beginning to replace most conventional light sources.
The term solid state lighting is used because the electronics produces light directly from solid materials in which the electrons are embedded. It is unlike other technologies, for example fluorescent technology, which requires a gaseous discharge medium to initiate production of light.
LED technology is constantly changing. Rapid innovation continues to improve the performance of LED on an almost daily basis. Future-proofing of LED modules allows luminaire manufacturers to switch from one generation to the next improved generation without major retooling or changes in luminaire design, offering backward compatibility with drivers.
LED chips are mass produced in millions and there are inevitably slight differences in color appearance and light output. Binning is way of sorting the chips so that all the LEDs from one particular bin look the same and have similar light output.
A light engine is the LED equivalent of a conventional lamp. It normally consists of a LED chip mounted on a circuit board that has electrical and mechanical fixings, meaning it is ready to be fixed in the luminaire. Note that the light engine may not consist of only one chip; it may be an array of 9 or 16, sometimes with a phosphor coating.
LEDs have no gases, filaments, and no moving parts to fatigue. They provide light through a one-step process that takes place within the diode. There is no glass to break or screwed contacts to loosen.
LEDs are made of electronic components that need to be packaged together to offer long-lasting efficient light sources to the end user. Apart from the LED chip itself, which has sapphire and gallium in the semiconductor, the process of packaging with materials like ceramic, rare earth phosphors, silicone, solder, and gold wire add to the overall cost. White LEDs require further tests for calibration and standardization.
Although the initial cost of conventional light sources is less than LEDs, the operational and maintenance costs of LEDs are significantly lower. LEDs, having a longer life, reduce maintenance and lamp replacement cost. As LEDs need to be replaced less frequently, the owner spends less on new lamps and the labor needed to change them. LEDs also consume less energy; thus the overall cost of a LED system can be significantly lower than that of a conventional lighting system. Most applications with LEDs offer a payback period as low as three to four years.
Some of the strategies for reducing the cost of LEDs in the future are:
Here are some of the aspects that need to be taken into consideration:
Lights built into wardrobes can be of the following types:
LEDs can produce concentrated beams of light at specific light frequencies. While sunlight comprises the entire spectrum of light, LEDs can be designed to emit specific parts of the light spectrum that activate certain photoreceptors in the plant. For example, blue light promotes phototropism and cryptochromes, which contribute to germination and elongation of the plant, while red light stimulates phytochromes, which help the plant to flower at the optimum time. Regulation of the spectrum of light based on the plant’s life cycle promotes faster growth, and a stronger plant than what would be grown under sunlight conditions.
Note that the light output of LEDs lessens at higher temperatures. You should make sure that the luminaire is suitable for the environmental conditions.
Most insects are primarily attracted to ultraviolet rays, which help them forage, navigate, and select mates. For example, Indian moths are attracted to UV light (365nm) and green light (500nm). LEDs do not have UV content and hence do not attract many insects compared to conventional light sources.
LEDs do not emit ultraviolet light and do not carry heat in the beam, unlike their conventional counterparts. This helps keep food fresher in refrigerators and cold stores.
LEDs have the following advantages over neon:
It is important to compare the spectral power distribution of the light source (SPD), Color Rendering Index (CRI), Correlated Color Temperature (CCT), and the Color Quality Scale (CQS) of the light source depending on the nature of exhibits/displays to be lit. The illumination level needed within the exhibition and the hours of operation also need to be considered. This is a specialist area, and proper set up of lighting requires the advice of a consultant such as the curator.
In retail and display environments where the range of products changes by the season, the colors can be changed to match the type of product on display. For example, electronic goods may require a cool white light, while a warmer tone may be required for fabrics. When a fashion season has red as a theme, the store can use a color of light with more red in its spectrum to enhance and bring out the vibrancy of the display.
LEDs offer the capability of changing from warm white to cool white through digital control of the LEDs. This can be used in indoor or partly outdoor environments where the illumination level and color temperature can be adjusted to match the outdoor conditions (e.g. sunny, clear sky, or overcast) depending on the feel required in the space.
Using LEDs in mining areas has the following benefits:
LEDs have the capability to offer “biologically optimised” solutions that simulate the color temperature of the sky. This have been proven to improve concentration and maintain alertness of students in classrooms. It has successfully dealt with a kind of morning tiredness typical to young people. One way of creating the appropriate color temperature is by using a combination of independently controlled blue and white LEDs.
Use of tunable LEDs in aircrafts can help alter the circadian rhythms of passengers. The time-controlled simulation of daylight, noon, and dusk color temperatures with the LEDs in the aircraft can help passengers to gradually adapt to the time zone of the destination.
Underground stalactites are damaged by the heat of halogen lamps. Apart from having long lifecycle, LEDs also require much less maintenance than traditional light sources.
LEDs work more efficiently in cold temperatures. Better still, the cold air that offers a passive heat absorption extends their lifecycle. This gives LEDs an advantage in various applications like ice-skating rings/tracks, cold storage places, and lighting public places in colder countries.
The recent development of LEDs allows them to not only provide light, but also offer internet connectivity through “Li-fi” technology. By increasing the flicker rate of LEDs, data can be transmitted to specially adapted laptops and electronic devices via the visible spectrum, instead of via the currently used radio and microwaves.
Zhaga is an industry-wide consortium aiming to standardize specifications for interfaces between LED luminaires and light engines. The aim is to permit interchangeability between products made by different manufacturers. Zhaga defines test procedures for luminaires and LED light engines so that the luminaire will accept the LED engine.
CELMA is the Federation of National Manufacturers Associations for Luminaires and Electrotechnical components in the European Union. CELMA, along with ELC (European Lamp Companies Federation), provides standards and guides for LED lighting in Europe.
IP (Ingress Protection) ratings or UL (Universal Laboratories) ratings are commonly used to determine LED product suitability for various harsh, underwater, or outdoor applications.
In Europe, every light fitting must have a CE label, which defines the seller’s claim that the fitting conforms to all relevant European safety standards. The most important of these is EN 60598, which covers electrical, thermal, and mechanical safety.
PAS is the Publicly Available Standard, an informal rating used in Europe. While it is not a formal EN standard, it is an industry-agreed way of presenting data and procedures.
LEDs are low-voltage devices. Therefore, the LEDs require a device/power supply unit/driver or integrated electronics that convert line voltage to low voltage in order to run them. Sometimes, the driver has electronics that can interpret control signals to dim LEDs.
LEDs are driven by constant current (350mA, 700mA, or 1A) drivers or constant voltage (10V, 12V, or 24V) drivers. Constant current drivers fix the current of the system and vary the voltage depending on the load of the LED. Constant voltage drivers require a fixed voltage, and the LED loads are added in parallel across the output of the driver until maximum output currents are reached.
Constant current drivers are typically used in downlights where one or a series of luminaires is used per driver. These are connected in series.
Constant voltage drivers are used in applications where the load is not known and the LED loads are connected in parallel, for example in coves and signage applications. These drivers are sometimes similar to the low voltage electronic and magnetic transformers used in halogen light fixtures (MR16 lamps). The type of LED driver suitable to run a LED product is stated by the LED manufacturer in the product specification.
The LED rating of a product is usually noted in milliamps (mA) or volts (V). Products rated in mA can be used with a constant current driver, while those rated in Volts can be run with a constant voltage driver. LEDs designed for constant current drivers cannot run with constant voltage drivers without damaging them.
Vf is the term used for the LEDs forward voltage. It is the voltage required to activate the LED and produce the output specified, assuming that it is drawing the recommended current.
The maximum permissible distance is dependent on the LED load, conductor size, and the driver used. There is little practical limit on the distance between the driver and LED if you are using a constant current driver because it increases the output voltage to overcome any Volt drop caused by the cable length. The distance between the LED and the driver is more important for constant voltage drivers where there is a voltage drop due to the load and length of cable.
LEDs driven by 24V drivers have longer permissible distances between light source and driver compared to 12V DC LEDs. 12V LEDs are usually suitable for applications where low light outputs are required. 24V LEDs offer products with higher outputs than 12V products.
LEDs are inherently low-voltage devices that require drivers. However, many LED products in the market come with built-in drivers and hence can be directly connected to the mains voltage.
LED drivers need to be mounted in a ventilated space. Access to the driver needs to be provided for general maintenance purposes. The IP (Ingress Protection) rating of the driver needs to be considered before finalizing the mounting location of the driver (only those drivers designed for outdoor environments can be located outdoors). The distance between the driver and the light source needs to be taken into consideration in order to prevent a voltage drop, which results in reduced output of the LEDs.
LEDs are dimmed either by Pulse Width Modulation PWM or Constant Current Reduction CCR. PWM dimming involves switching current at a high frequency from zero to the rated output current. As for CCR dimming, the lighting level required is proportional to the current flowing through the LED. Current flows through the LED continuously and is reduced or increased based on whether the LED is to be dimmed further or made brighter.
The following are the advantages of PWM dimming:
The following are the disadvantages of PWM dimming:
CCR dimming is good in:
Although LED products are marked as compatible with traditional dimmers, there are various degrees to which LED products are compatible with incandescent dimmers. Compatibility needs to be checked and tested on a product-by-product basis for the following most common undesirable behaviors:
Analogue dimming is usually referred to as 1 - 10V dimming. In this case, a DC voltage is sent to the driver, which dims the LEDs in response to the voltage. With digital dimming, the driver receives a digital signal which tells it how to respond. The advantage of digital dimming is that fixtures are addressable. You can also have many more different levels of light output when using digital dimming.
For applications where single colors and white LEDs are used, analogue or PWM dimming protocols can be used to switch or dim LEDs. For intelligent controls like creating dynamic effects, tuning of white light, and more, DMX or Ethernet protocols can be used. Digital dimming works better with large numbers of luminaires.
This is usually due to incompatibility between the driver and the control system. When purchasing an LED product, it is important to use the correct driver type as specified by the manufacturer. It is also important to check that the LED is dimmable. Some retrofits are not.
Heat management is critical for the performance of LEDs. Increasing heat in LEDs has the following effects on performance characters:
The two-phase heat exchange technique is a cooling technique that uses the advantages of both active and passive cooling methods.
It works on the principles of evaporation and condensation. The process requires disposable heat to initiate the process that happens in a hermetically sealed tube that is filled with a minute quantity of liquid. The system has cooling fins around the tube to dissipate heat. This system offers high reliability and zero operation costs. Plus, it is not orientation dependent.
Junction temperature is the LED’s active region; the point at which the diode connects to the base. This is where the electrons jump between the two semiconductors to produce photons. A low junction temperature helps LEDs to produce more light, while also reducing lumen depreciation. Junction temperature is affected by the driver current, the thermal path, and the ambient temperature.
The following are the types of optical systems for LEDs:
LEDs are directional sources of light as opposed to traditional luminaires, which are omni-directional. When LEDs are fitted with reflectors, much of the light at the center of the beam passes out of the system without even touching the reflector. This reduces the scope of modulation of the light beam and can be the cause of glare. Lenses, however, help guide virtually every ray of light emitted by the LED.
Here are the few ways in which glare can be reduced from LEDs:
No. It is true that there is no heat, IR, in the beam. However, the LED fixture itself, does produce heat. However it may become warm or hot, to the touch.
The LED chip or light engine produces heat. This needs to be dissipated as quickly as possible. This is normally done with a heat sink, which often has fins. Cool LEDs are more efficient than hot ones. They also have a longer life. Of course, higher power LEDs generally run hotter than low power ones because of the extra heat to remove.
50,000 hours would imply 5.7 years if the light is operated for 24 hours a day, 7.6 years if the lights are on 18 hours per day, and 11.4 years if the light functions for 12 hours a day.
Unlike conventional light sources that reduce in output and eventually fail, LED products do not normally suddenly fail. Instead, the light output reduces over time.
The normal convention is to measure the life from when the output has reduced by 30%, i.e. when there is 70% light output remaining. This is often quoted as the L70 life and is measured in hours.
The thermal management of LEDs. If LEDs come on a standalone chip, appropriate heat sinks have to be designed to prevent premature failure of LEDs.
The electrical stress: Running LEDs at currents higher than specified make the LED run hot. This can happen with wrongly matched drivers. For example, if the driver produces 700mA, but the LED needs 350mA, this will put stress on the LED and reduce its lifespan.
Higher ambient temperatures than the ones that the LED is rated for will reduce its expected life.
Unlike discharge lamps, LEDs are semiconductors and their lifespan is not affected by the number of times they are turned on and off.
Typically, an LED will last four times longer than a CFL and 25 times longer than an incandescent source that puts out the same amount of light.
Sometimes simply comparing the lumen output of LEDs and conventional light sources may not be adequate. The amount of light falling on a specific task area (the lux) gives a more realistic comparison. You should also consider the amount of illumination visible on walls. This helps identify applications where LEDs offer better solutions than other light sources.
This may occur if you are using the same product from the same brand, with the same optics and hardware. However, in general, the nature of the components (like the optical system, heat sink, LED chip, and the driver) affects the output more than the wattage does. A 3Watt LED luminaire from one manufacturer will have a different output compared to a 3Watt LED luminaire from another manufacturer, even if the same LED chip is used. Hence, using a high-quality chip alone does not guarantee better performance. Note that as the wattage increases, the efficiency drops slightly. An LED driven at 3W will emit slightly less than three times the output of the one driven at 1W.
When comparing the lumen output between LEDs and conventional light sources, LEDs may have lower lumen value in many cases. However LEDs are directional light sources, all the lumens emitted from an LED are directed towards the task area. Conversely, conventional sources emit light in all directions. The light is then modulated in a given direction with optical systems like reflectors and lenses. The amount of lumens that falls in the intended task area from an LED light source is greater than that of a conventional light source.
Absolute photometry measures very precisely the lumens emitted by a specific luminaire, while relative photometry can be adjusted to measure light distribution by various lamps with different lumen outputs. Most LEDs are permanently fixed in the luminaire along with its optics. Replacement in case of premature failure means replacing the whole luminaire and not just the light source. The lumen performance of LEDs is best evaluated by considering the various accessories the light passes through (lenses, reflectors, etc.) before it falls on the surface to be lit. As a result, absolute photometry is the method usually used to measure LED performance. Note that some luminaires have replaceable LED modules, but the same arguments apply.
The lumen output of an LED is dependent on the thermal management/heat sink design, electrical characteristics such as the junction and rated ambient temperature, driver currents, and the optical system. This means that the light output is very much dependent on the design of the actual luminaire. This is unlike other light sources like HID where the photometrics of a luminaire are fairly independent of the lamp used.
These terms do not have any photometric or engineering meaning. However, "cold lumens" is the light output of the LED chip alone when it is first switched on. "Hot lumens", refers to the light output of the LED when it is fully warmed up in the luminaire. The hot lumen value may be 30% - 50% lower than the cold lumen value.
LEDs are more efficient than most other light sources, so they usually consume less energy for a given task or at a specific light output. Also, they do not contain hazardous materials such as toxic mercury. Moreover, LEDs have a longer lifespan and hence reduce the frequency of disposal of lamps.
LEDs normally use less power for a given application compared to traditional halogen and fluorescent sources. As such, the overall kW/hr consumption per year is less, which helps reduce the overall CO2 emissions.
LEDs are primarily made of electronic components like PCBs, diodes, semiconductors, etc. Therefore, they must be treated in the same way the traditional electronics are. They are collected separately from household wastes and must be treated the same as standard electronic equipment.
Most retrofits have the appearance of a conventional lamp and are used as a direct replacement for the existing one, i.e. they have a screw or bayonet cap base. With downlights and spotlights, it's common to have a 50mm dia reflector lamp. The mains voltage ones are usually called GU10, which refers to the flattened pins on the base. However, some are available for 12V supply fed from a transformer, e.g. direct replacements for 50mm dichroic LV downlights. These will have thinner pins and are often called MR16 or GU5.3 lamps.
As with complete LED luminaires, it is important to ask the supplier for the lumen output and to compare this with the unit you are replacing. If it is a spotlight, compare the two lamps side by side. Poor quality sales literature often states the output from the LED chip and not the complete lamp.
Retrofit lamps are offered with various white light outputs, ranging from warm to cool. This is often indicated on the packaging. Typically, it might say “2700K Warm White” or “4000K Cool White.” The bigger the number, the cooler is the appearance.
The general answer is no. The electronics in the retrofit will overheat and lead to a short lifecycle. A better solution is to use an LED module with a remote driver.
Most LED tubes, although they have the same size, lamp base as a linear fluorescent, and possibly a similar lumen output, do not have the same omni-directional light distribution. Many luminaires emit 20%-30% less light output with narrower beam spreads when fitted with LEDs. This is especially true of troffers with reflectors that offer batwing (widespread) light distribution with fluorescents. This needs to be taken into account when considering the overall 30-50% less power usage by LEDs with increased system efficiencies. It is likely that the luminaire will need some rewiring and this should be done in conformance with the local electrical installation standards.
Light emitting diodes produce light by the movement of electrons between the two terminals of diode, which occur by a process called electroluminescence. When a light emitting diode is electrically connected, electrons start moving at the junction of N-type and P-type semiconductors within the diode. When there is a jump over electrons at the p-n junction, the electron loses a portion of its energy. In regular diodes this energy loss is in the form of heat. However, in LEDs the specific type of N and P conductors produce photons (light) instead of heat. The amount of energy lost defines the color of light produced.
A typical LED is made with a chip, which is the semiconductor that produces the light when electrically connected. The chip is connected by a very thin bond wire to provide electrical contact that acts as the cathode. The chip is bonded with a thermal heat sink and a ceramic base. The chip is enclosed by a lens that not only protects the chip, but also modulates the light beam to the desired angle, depending on the nature of the lens. For production of white light, the chips are coated with phosphor.
LEDs produce light by direct conversion of electrical energy to light energy. On the other hand, incandescent light sources produce light by heating a filament until it grows red hot. Linear and compact fluorescent lamps use a UV discharge plus a phosphor to produce the light. HID lamps use the ionization of gases in a discharge tube which produce photons.
O-LEDs are organic light emitting diodes. They are made of carbon based films sandwiched between two electrodes; one is a metallic cathode and one is a transparent anode, which is usually transparent glass.
O-LEDs are two thin, flat dimensional surfaces, offering a soft, glare-free luminous surface. Some versions of O-LEDs are flexible. They can be transparent, mirrored, or diffused when not electrically connected.
LEDs do not directly produce white light. There are two ways in which white light is produced by LEDs as below:
Tunable white LEDs are light engines that combine individual chips to produce a range of CCT from warm white and cool white.
The light color is dependent on the inorganic material used in the P-type and N-type semiconductors (organic material in the case of O-LED). Different inorganic materials in the semiconductor release different amounts of energy when the LED is connected to a power supply. The amount of energy released defines the color of the light produced. For example, red is low-energy light and blue is high-energy light.
LEDs emit a very narrow spectrum of light. The type of material used in the semiconductor permits only a specific wavelength of light (one color) to be emitted when electrons cross the junction.
The RGB LED means red, blue, and green LEDs. RGB LED products combine these three colors to produce over 16 million hues of light. Note that not all colors are possible. Some colors are “outside” the triangle formed by the RGB LEDs. Also, pigment colors such as brown or pink are difficult or impossible to achieve.
The following are the different types of RGB LEDs:
This is a phosphor - converted Amber LED. Amber uses special phosphors in combination with royal blue LED chips.
These are chemical symbols used for materials used in the manufacturing process of LEDs to generate specific colors.
Color temperature defines the color appearance of a white LED. CCT is defined in degrees Kelvin; a warm light is around 2700K, moving to neutral white at around 4000K, and to cool white, at 5000K or more. Note that CCT does not tell you anything about the color rendering ability of the LED.
The thickness of the phosphor layer and the wavelength of the blue chip influence the color temperature of the LED.
Color Rendering Index - CRI indicates the accuracy with which a light source such as an LED can reveal the various colors of an object. The standard CRI system is based on eight colors across the spectrum.
Additional R-values of CRI are used to represent certain colors. The appropriate R-values are application specific. For example, R9 represents red and is good for lighting flesh. It also tends to make the light warmer.
Color Quality Scale CQS is a new system that uses a wider palette of 15 reference colors against the smaller palette of 8 reference colors used for the CRI system.
The CR-9 represents red tones, which are prevalent in skin tones, clothes, vegetable, and meat. For make-up rooms, supermarket, and grocery meat and vegetable counters, if the same visual freshness as seen with halogens and incandescent lights sources is required, looking into R-9 values of LEDs is a must. Usually, gallery owners and artists will easily note the difference in effect when red tones are prevalent in the art work.
SPD is the Spectral Power Distribution of a light source. The visible white light that we see is made up of a spectrum of various colors of light, ranging from wavelengths of 380nm (violet) to 760nm (red). The SPD is a graph that shows the power (strength) of each wavelength of light produced by a particular light source.
This is an elliptical region on the CIE chromaticity diagram that contains all the colors that are indistinguishable to the average human eye, from the color at the center of the ellipse. Adjacent ellipses are “just distinguishable” in terms of color. This system is used to refine the binning process of LED colors. Slight color differences in the appearance of LED light are measured in MacAdam ellipses or steps.
LEDs are standardized for consistency in color and performance through a process called binning, and they are classified further in the MacAdam steps. During the manufacturing process LEDs are allocated to specific 'bin' numbers based on tests conducted to determine their color, lumen output, and forward voltage. LEDs from each bin are further classified in a 7-step MacAdam ellipse.
Apart from CRI, R-values, and CQS, color consistency is also a measure of the quality of light. The color consistency can be evaluated at several levels as follows:
The white LEDs are made of a phosphor coated blue LED chip. The degradation of the phosphor layer over time causes the bluish tone of the light emitted. This degradation is most likely to be caused by the chip running too hot. Remote phosphor technology overcomes this issue.
There are several possible reasons why this happens:
The remote phosphor process offers:
Here are the various terminologies for developmental stages of LED in chronological order:
SMD means surface mounted diode. This is a better technology than the first generation DIP LEDs. The SMD type LEDs are mounted on an aluminum substrate and enveloped in an epoxy resin.
The advantages of SMD over DIP LEDs are:
The basic types of chip LEDs are:
LED modules may be available in the following forms:
Zigbee is a technology developed by a global alliance of companies to create wireless solutions for energy management. These solutions include a new open standard for LED lighting controls.