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What are LEDs?


LEDs are Light Emitting Diodes. These are electronic components that produce light by conversion of electrical energy directly to light by the movement of electrons within the material of the diode.


Why is LED technology classified as solid state lighting?


The term solid state lighting is used because the electronics produce light directly from solid materials in which the electrons are embedded. This is unlike other technologies; for example fluorescent technology that requires a gaseous discharge medium to initiate production of light.


What is Future-proofing of LED products?


LED technology is constantly changing. Rapid innovation continues to improve the performance on a 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.


What makes LEDs more robust than other light sources?


LEDs have no gases, filaments or any 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.


Why do LEDs have a higher initial cost than conventional light sources?


LEDs are made of electronic components which 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 standardisation.


What are the economic advantages of using LEDs over conventional light sources?


Although the initial cost of conventional light sources is less than LEDs, they do not take into account the operational and maintenance cost of the lighting system. LEDs, having a longer life, reduce maintenance and lamp replacement cost. This reduces cost of labour to replace lamps and the cost of new lamps at the end of lamp life cycle. LEDs, also consume less energy. Thus the overall cost of a LED system can thus be significantly lower than conventional lighting systems. Most applications with LEDs offer a payback period as low as 3-4 years.


What are the strategies in the development of LED technology that are helping to reduce the cost of LEDs in the future?


Some of the strategies reducing the cost of LEDs in the future are:


  1. Reduction in the production process.

  2. Simplification and reduction in the number of components.

  3. Introduction of new materials.


What are the considerations that need to be taken into account when integrating LEDs into interior/architectural elements or furniture?


Here are some aspects that need to be taken into consideration:


  1. The luminaire spacing and layout.

  2. Preventing a view of the light source and minimising glare.

  3. Ventilation/cooling of LEDs

  4. Wiring access to LEDs in case of maintenance or replacement.

  5. Location of driver, if not integrated in luminaire.

  6. Switching / dimming or control type and location.


What aspects need to be taken in consideration when replacing a light source with LEDs in a retrofit scenario?


The lamp base/holder screw fixing position. The physical dimension of the LED lamp and how it fits into the existing housing. The electrical characteristics of LEDs compared to the existing system (mains voltage, low voltage, control methods). The location and size of the light emitting surface in relation to the luminaire reflector and in comparison to the original light source. The light distribution, lumen output and other photometric properties like colour temperature and colour rendering in comparison to the original light source. The heat generated by the LED during operation and the maximum operating temperature.


Is it true that LED lights do not attract insects?


Most insects are primarily attracted to Ultra-violet rays to help them forage, navigate and select mates. For example Indian moths are attracted to UV-365nm and green light-500nm. LEDs do not have UV content and hence do not attract so many insects compared to conventional light sources. Some products that are being released claim to have light wave lengths that actively repel insects.


What are the advantages of LED over neon in signage applications?


LEDs have the following advantages over neon:


  1. Power consumption: LEDs use much less power required than neon to deliver the same light output. 

  2. LEDs offer a far wider a range of products and configuration of solutions than neon.

  3. Neon has limitation due the nature by which they produce light and fabricated.

  4. Heat dissipation: LEDs produce less heat than neon

  5. Safety: Neon runs on high voltage and are unsafe to be located in places where public can touch.

  6. Neon uses fragile glass tubes.

  7. LEDs offer a wider palette of colour and colour changing effects through digital control.

  8. Maintenance: LEDs virtually need no maintenance compared to neon.


How can the colour changing facility of LEDs be advantageous in retail and display environments?


In retail and display environments where the range of products change by the season, the colours 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. A fashion season which has red as a theme can utilize a colour of light with more red in its spectrum to enhance and bring out the vibrancy of the display.


How can flexibility in changing colour temperature offer more comfortable environments?


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 illuminance level and colour temperature can be adjusted to match the outdoor conditions (sunny, clear sky day or overcast day) depending on the intended feel required in the space.


Can mains voltage LED products be dimmed with traditional incandescent dimmers?


Although LED products are marked as compatible with traditional dimmers, there are various degrees to which LED products are compatible with incandescent dimmers. This needs to be checked and tested on a product by product basis for the following common undesirable behaviours; Reduced dimming range, Flickering of the lamp, inconsistent performance based on the number and different types of LEDs connected to a single incandescent dimmer.


What are the advantages of dimming LEDs?


Dimming LEDs offer the following advantages: Saving energy, because less energy is used for reduced output levels and  extended life due to the electronic components run cooler. This not only extends the life of LEDs but also increases the life of the phosphor coating that is used to produce white light. Furthermore an advantage of dimming LEDs is the asssitance to designers creating ambient lighting presets to create mood settings. Moreover, flexibility in usage of space is affected. A brightly lit space for reading or an office space can turn into a presentation/conference area by dimming. Thus, potentially increasing productivity by individual control to reduce eye strain and fatigue or to improve concentration. 


What is the difference between analogue and digital dimming?


Analogue dimming is usually referred to as 1 - 10v dimming. In this case, a DC voltage is sent to thedriver 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.


What lighting protocol is appropriate for an application?


For applications where single colours 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 etc, DMX or Ethernet protocols can be used. Digital dimming works better with large numbers of luminaires.


Why do some LEDs flicker when dimmed or turned off?


This is usually due to incompatibility between the driver and the control system. When purchasing an LED product, it is important to use the driver type as specified by the manufacturer. Also it is important to check that the LED is dimmable. Some retrofits are not.


Why is the heat sink design critical for the performance of an LED fitting?


Heat management is critical for the performance of LEDs. Increasing heat in LEDs has the following effects in performance characters:


  1. Reduction in luminous fluxColour shift (change in colour appearance).

  2. Reduction in life of the LED.


What are the heat transfer techniques used to cool LEDs?


LEDs are cooled either by passive cooling or active cooling. Passive cooling involves a finned heat exchange system made of cast or extruded metal or plastic coated metal heat sink, that offers a totally silent, robust, heat transfer. Passive cooling is reliant on the surface area of heat sink material and is orientation dependant. Active cooling may include conventional fans or diaphragm- based forced air cooling. Active cooling using a fan, although more efficient; is noisy, not so reliable, and needs electricity to run. Active cooling lays emphasis on forced air flow rate and is not orientation dependant.


What is the two-phase heat exchange technique of cooling LEDs?


Two-phase heat technique is a cooling technique that uses the advantages of both active and passive cooling methods.It works on the principle of evaporation and condensation. The process requires disposable heat to initiate the process that happens in a hermitically 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, zero operation costs and is not orientation dependant.


What is junction temperature?


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 and also reduce the lumen depreciation. Junction temperature is affected by the driver current, the thermal path and the ambient temperature.


What are the different types of optical systems for LEDs?


The following are types of optical systems of LEDs: Primary systems with integrated lenses - specific beam angles. Secondary optical system in the form of lenses, reflectors or diffusers. Combination of primary and secondary optics for specific applications.


Why are lenses preferred over reflectors for many LED luminaires?


LEDs are directional sources of light rather than omni-directional from traditional sources of light. For LEDs with reflectors, much of the light at the centre of the beam passes out of the system without even touching the reflector. This reduces the scope of modulating the beam of light and is a very visible source of glare. Lenses help guide virtually every ray of light emitted by the LED.


What are common challenges or problems when using LED fixtures in harsh environments?


The LED drivers can fail early due to ingress of moisture or condensation. The driver enclosure needs to be properly sealed.LEDs are less resistant to damp than other light sources. This means that particular attention needs to be given to the light fixture seal and cable glands. What are the various causes of condensation within LED luminaires?Heat build up as the luminaire is turned on and cools down when it is switched off. Pressure formed due to change in altitude and environmental conditions during transportation as cargo or in planes. Thermal shock due to rain, snow or washing cycles. What are the product features to look for in LEDs used in harsh environments? Integration of more rugged O rings and gaskets for more robust seals. Providing thicker enclosures to prevent movement around seals to prevent breakage of seals. Providing additional bolting around gaskets and seals to prevent snapping of seals. Provide a vent made of two-way permeable membrane. This allows water vapour and gas to pass through but not liquid water.


Is it true that LEDs do not produce heat?


No. It is true that there is no heat, IR, in the beam. However, the LED fixture, itself, does produce heat. It may become warm, or hot, to the touch. The LED luminaire is hot to touch.


Why is this?


The LED chip, or light engine produces heat. This needs to be dissipated as quickly as possible. This is normally by using a heat sink. This 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. Back 5. Life and Light output.


What does a life of 50,000 hours mean in the case of LEDs?


50,000 hours would imply 5.7 years if the light is operated for 24 hours in a day, 7.6 years if the lights are on 18 hours per day and 11.4 years for 12 hours a day.


Why is the life of LEDs measured as lumen depreciation?


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 quote the life 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. What are the factors that affect the lifespan of the LEDs? The thermal management of the 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. E.g. the driver produces 700mA whereas the LED needs 350mA stresses the LEDs and reduces its lifespan. Higher ambient temperatures than that for which the product is rated reduces the life of the LEDs.


Is lifespan reduced if the LEDs are frequently turned on and off?


Unlike discharge lamps, LEDs are semiconductors and their life span is not affected by the number of times they are turned on and off.


How much longer does an LED last than a conventional light source?


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. What is the best way to compare the output of LEDs with other light sources? Sometimes simply comparing the lumen output of LEDs and conventional light sources may not be adequate. The amount of light falling on specific task area (the lux) gives a more realistic comparison. You should also consider the illumination on the walls. This helps identify applications where LEDs offer better solutions than other light sources.


Does increasing the wattage of LEDs increase their output?


This may be true if it the same product from the same brand with the same optics and hardware used. However; in general the nature of the components like the optical system, the heat sink, the LED chip used and the driver affects the output more than by just the wattage. A 3watt LED luminaire from one manufacturer will have a different output from a 3watt LED luminaire from another make, 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 driven at 1W.


Why are LEDs considered more efficient than conventional light sources?


In many cases when comparing the lumen output between LEDs and conventional light sources, LEDs may have lower lumen value However LEDs are directional light sources. All the lumens emitted from an LED are directed towards the task area; while conventional sources emit light in all directions which are then modulated in a given direction with optical systems like reflectors and lenses. The proportion of lumens that falls in the task area from an LED light source is greater than that of a conventional light source.


Why are LEDs considered green technology?


LEDs are more efficient than most other light sources, so they usually consume less energy for a given task or 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.


How are LEDs beneficial in developing countries?


Many areas in developing countries use kerosene or bio-mass as fuel for lighting, which degrade the environment and emit large amounts of CO2. LED technology offers light with minimal wattage that can be generated by micro power generators like solar panels and hydroelectric systems.


How can LED lighting help reduce CO2 emission?


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, so this helps reduce the overall CO2 emissions.


What you need to know about replacing an existing lamp with an LED Are all retrofits main voltage?


Most retrofits have the appearance of a conventional lamp and are used as direct replacements for the existing one. I.e. they have a screw or bayonet cap base. In 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.


Are they all the same size?


No. You should check that the replacement unit will fit the luminaire. Many have slightly different dimensions from the lamp they are replacing. It may be necessary to get a sample of the retrofit lamp to ensure it fits your particular light fitting.


Will the light output be the same?


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. 


Why is this?


Retrofit lamps are offered with a range of white light 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.


Can I put a retrofit in an enclosed or sealed luminaire?


The general answer is NO. The electronics in the retrofit will overheat and lead to a short life. A better solution is to use an LED module with a remote driver.


Can linear LEDs be used as a substitute for T8 or T5 fluorescent lamps?


Most LED tubes, although they have the same size, lamp base and possibly a lumen output close to that of linear fluorescent; do not have the same omni directional light distribution of linear fluorescents. Many luminaires, especially troffers with reflectors that offer batwing (wide-spread) light distribution with fluorescents; emit 20%-30% less light output with narrower beam spreads with LEDs. 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.


What are the core components of a typical LED that gets soldered to a Printed Circuit Board?


A typical LED is made up of the chip which is the semiconductor that produces the light when electrically connected. The chip is connected by a very thin bond wire to a lead 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 dependant on the nature of the lens. For production of white light; the chips are coated with phosphors.


Do LEDs require time to reach maximum brightness?


No. LEDs directly convert electrical energy to photons. It is a one step process of electroluminescence that does not require time to reach maximum output. Other sources such as fluorescents or HID work on discharge technology. This requires an arc to warm up and may take a few minutes to reach full output.


Why do LEDs produce more vibrant and saturated colours than conventional lamps?


LEDs emit a very narrow spectrum of light. The type of material used in the semiconductor permits only a specific wavelength of light (one colour) to be emitted when electrons cross the junction.


What does RGB LED mean?


RGB LED means red, blue and green LEDs. RGB LED products combine these three colours to produce over 16 million hues of light. Note that not all colours are possible. Some colours are “outside” the triangle formed by the RGB LEDs. Also, pigment colours such as brown or pink are difficult, or impossible, to achieve.


What are the different types of RGB LEDs?


The following are the different types of RGB LEDs:R/G/B/W - Has an additional White LED. This is often used where you need a pure white as well other combined colours. RGB / 3 in 1 LED - A red, a blue and a green LED chip are mounted within a common light engine and focussed through a lens to produce a more uniform hue across the beam of light. RGBW / 4 in 1 LED - similar to the RGB LED but with a warm white LED integrated in the light engine to offer more colour tones. RGBA - Has an additional Amber LED chip.


What are the standard comparisons used to evaluate the colour quality of light sources?


Colour Rendering Index - CRI indicates the accuracy with which a light source such as an LED can reveal the various colours of an object. The standard CRI system is based on eight colours across the spectrum. Additional R-values of CRI are used to represent certain colours. The appropriate R-values are application specific. For example R9 represents red and is good for lighting for lighting flesh. It also tends to make the light Warmer. Colour Quality Scale CQS is a new system that uses a wider palette of 15 reference colours as against the smaller palette of 8 reference colours used for the CRI system.


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