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. They are important because due to their efficiency and low energy, they are beginning to replace most conventional light sources.
What are the advantages to using LED luminaires?
LEDs bring several advantages to the lighting industry, including high efficacy and durability, and, with superior life over other lamp sources, their required maintenance is greatly reduced. This translates into energy savings, maintenance savings, and environmental sustainability. There is also the potential for greater optical control (more controllable source), dimming, instant on/off, and reduced rate of lumen depreciation (potential for long application life).
Why does the identical LED chip package lumen depreciate at different rates from manufacturer to manufacturer?
Unlike previous technologies, LED manufacturers have a much greater impact on the rate of lumen depreciation based on their luminaire designs. Thermal design plays a critical role in the rate of lumen depreciation.
Do LED lights produce UV and/or IR emissions?
Unlike incandescent and fluorescent light sources, LED Lighting products produce virtually no light in the ultraviolet (UV) or infrared (IR) spectrums.
What does "Lifetime 50,000 hours" mean?
Useful life has been defined as the number of hours an LED device can operate until it emits only a certain percentage of its original lumen output. For general illumination applications, vision research suggests that 70 percent of original lumen output is the level where end users begin to notice a drop in light levels. This metric is indicated as L70. L70 life after more than 6,000 hours of testing and got the number 50,000 hours under normal operating conditions. Please note, any initial condition or parameter change will affect the useful life of LEDs in different ways.
Why are LEDs considered a GREEN technology?
Just imagine the benefits of choosing LED: • No concern over proper disposal (hopefully not simply thrown in a landfill) of old HID lamps containing harmful mercury. • No fuel used and the accompanying pollution to service those fixtures. • Greatly reduced potential for lane closures and other productivity and inconvenience-related costs associated with maintaining an HID system. • No natural resources lost to produce the replacement lamps that contain mercury. • No fuel used to move old-technology lamps from the factory (most likely overseas), to the distributor, to the contractor, to the job site. It's important to keep in mind all the positive and powerful ripple effects that using LED technology can have on the environment.
How does ambient temperature affect LED efficiency?
LED fixtures must be designed with junction temperature thermal management as a key component and use the correct LEDs. These products will then be robust enough to operate in most ambient temperature applications. Unlike fluorescent sources, cold temperatures do not impact the performance of LEDs.
What is binning?
LED chips are produced in millions and there are inevitably slight differences in the 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.
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 standardization.
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 in comparison to the original light source. • The heat generated by the LED during operation and the maximum operating temperature.
Why do LEDs require power supply / drivers?
LEDs are low voltage devices. Hence they require a device / power supply unit / driver or integrated electronics that convert line voltage to low voltage to run the LEDs. Sometimes the driver has electronics that can interpret control signals to dim LEDs.
What are there different types of LED power supplies / drivers?
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 theLED. • 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.
Is it true that some LEDs can be directly connected to the mains voltage power?
LEDs are inherently low voltage devices and require drivers. However many LED products in the market come with built-in drivers and hence can be directly connected to the mains voltage.
What are the advantages of dimming LEDs?
Dimming LEDs offer the following advantages: • Saving energy, because less energy is used for reduced output levels. • Extended life; 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. • Helps designers create ambient lighting presets to create mood settings. • Flexibility in usage of space. A brightly lit space for reading or an office space can turn into a presentation/conference area by dimming. • Increases productivity by individual control to reduce eye strain and fatigue or to improve concentration.
What are the various control protocols that can be used for dimming LEDs?
LEDs are controlled directly by signals coming from the central dimmer or they can be designed to interpret other protocols like 1-10V, DMX, Ethernet or ZigBee signals from the central dimming system. The manufacturers of the LEDs recommend the various protocols their devices can understand.
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: • Reduction in luminous flux • Colour shift (change in colour appearance) • Reduction in life of the LED
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.
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.
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.
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.
How are LEDs different from other light sources in the way they produce light?
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 ionisation of gases in a discharge tube which in turn produce photons.
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.
What are tuneable white LEDs?
Tuneable white LEDs are light engines that combine individual chips to produce a range of CCT from Warm white and Cool white.
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 does correlated colour temperature, CCT, mean?
Colour temperature defines the colour appearance of a white LED. CCT is defined in degrees Kelvin where a Warm light is around 2700K moving to Neutral White at around 4000K to Cool white, 5000K or more. Note that CCT does not tell you anything about the colour rendering ability of the LED.
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.
What is a MacAdam Ellipse?
This is an elliptical region on the CIE chromaticity diagram that contains all the colours that are indistinguishable to the average human eye, from the colour at the centre of the ellipse. Adjacent ellipses are “just distinguishable” in terms of colour. This are used to refine the binning process of LED colours. Slight colour differences in the appearance are measured in MacAdam ellipses or steps.
What are the various types of LED chip packages available in the market?
The basic types of chip LEDs are: • SMD (Surface mounted diode) is a standalone chip on a ceramic base that can be integrated into various packages for linear LED strips or downlights. • COB (chip on board) LED comes as a high powered chip in direct contact with a printed circuit board optimal thermal management. • MCOB (multiple chips on board) LEDs are multiple COB LEDs integrated to form a single chip. This is used inLED bulbs and tubes. • MCCOB (multiple chips and cups on board) are used for high bay fixtures and floodlights.
Which wattage LED should I use to replace my existing lights?
Just like any properly designed lighting system, the correct wattage will depend on a few factors that all lighting suppliers should know and be able to use to recommend the correct fittings for you. However some good rules of thumb are: • Halogen Downlight to LED 5 - 1 Wattage Ratio e.g. 50W Halogen Downlight is roughly equivalent to a 10W LED fitting. • Incandescent Lamps to LED 7 - 1 Wattage Ratio • CFL Lamps to LED 2 - 1 Wattage Ratio • Linear Fluorescent Tubes 2 - 1 Wattage Ratio • Other Discharge lamps such as Metal Halide and Mercury Vapour to either LED or Induction Solutions are usually a 2-1 Wattage Ratio The above rules of thumb are just a guide, but always remember that BIGGER IS NOT ALWAYS BETTER, an over-lit room is just as uncomfortable as an under-lit room. A correctly selected lamp will light your space to the appropriate level, and keep your energy use to a minimum.
What is a lumen?
A lumen is a measurement of light output. Understanding lumen is becoming increasingly important as we transition from traditional light bulbs to LEDs. With incandescent lighting, most people associate brightness with wattage. A 100 watt bulb is brighter than a 75 watt bulb. However, wattage is really a measurement of power required to light the bulb and not a measurement of light output. A 60 watt incandescent bulb produces about 800 lumens of light. LED bulbs emit the same amount of light using 12 watts or less. It is the lumens that are important. The less wattage needed to power light, the better and more efficient your lighting. In the future, lumen output will be listed on bulb packaging. It will make it easier for the consumer to compare lighting, measure efficiency and design spaces with LEDs.