As per caveats of UNO ‘Electricity for lighting accounts for almost 20% of electricity consumption and 6% of CO2 emissions worldwide. According to the International Energy Agency, approximately 3% of global oil demand can be attributed to lighting. If not addressed immediately, global energy consumption for lighting will grow by 60% by the year 2030. This would have dramatic consequences for climate change’
In the world of lighting 20% of electrical energy is used for lighting, of which 40% is for incandescent lighting, this represents 2000×1012 Wh consumption per year. So it would be a significant impact on energy saving by replacing inefficient light sources such as incandescent lamps with more energy-efficient solutions.
DEVELOPMENTS OF LED
In late 1961, while working at Texas Instruments Inc. in Dallas, TX, James R. Biard and Gary Pittman found gallium arsenide (GaAs) emitted infrared light when electric current was applied. After that first visible-spectrum (red) LED was developed in 1962 by Nick Holonyak Jr., while working at General Electric Company. The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation in 1994 and was based on InGaN. The existence of blue LEDs and high-efficiency LEDs quickly led to the development of the first white LED, which employed a Y3Al5O12:Ce
With the rapid development in high brightness light-emitting diode (LED) technologies, both the performance and the cost of phosphor-converted white LED (WLED) have improved significantly. Due to its high efficacy (light output per watt), long life, and very low maintenance requirement, WLED is more and more accepted in general lighting applications
LIGHT EMITTING DIODE –L.E.D
A Light Emitting Diode (LED) is an electronic device that produces light when an electrical current is passed through it. The wavelength (or color) of light that is emitted is dependent on the materials from which the LED is made. LEDs are available in many colors, including red, blue, amber, green, and near-UV colors, with lumen outputs ranging from 10 lumens to 200 lumens.
The LEDs used predominantly in general illumination applications are “Phosphor Converted Blue” LEDs, which are blue LEDs that have a layer of yellow phosphor placed over the LED. The phosphor absorbs some of the blue light, and emits yellow light. When the unabsorbed blue light mixes with the yellow light it creates what your eye perceives as “white” light.
ADVANTAGES AND LIMITATIONS OF LEDS FOR GENERAL ILLUMINATION
Advantages
• High Efficacy (Lumens per Watt): LED-based lighting fixtures can achieve efficacies ranging from 25 LPW to over 80 LPW, compared to an incandescent efficacy of 5-10 LPW.
• Eco Friendly: LEDs do not contain hazardous materials as compared to mercury vapor in CFL bulbs.
• Longevity: LEDs can achieve useful lifetimes ranging from 25,000 hours to up to 100,000 hours, compared to ~1000 hours for an incandescent.
Limitations
• Controls compatibility: Due to the wide range of LED-based lighting product types, not all LED lamps are dimmable, and the ones that can be dimmed may be limited in dimming performance and system compatibility.
• Higher cost: High Brightness LEDs, necessary for general illumination, are expensive. They also require electronic drivers to convert conventional AC voltage to discrete DC voltages for the LED arrays.
DIMMING LEDs
Similar to fluorescent, incandescent and other conventional light sources, dimming LEDs saves energy at a roughly 1:1 ratio. This means that if you dim LEDs down to 50% of their light output you will save nearly 50% of your energy usage. So not only do you save by using a more efficient source, you save even more energy by dimming LEDs.
Dimming LEDs also makes them run cooler, which should extend the life of the electronic components of the driver, as well as the phosphor on the LEDs. This will extend their life, doubling or tripling the LEDs lumen maintenance. Research is ongoing to better quantify the relationship of dimming LEDs and lifetime extension. Dimming any lamp, be it incandescent, CFL or LED enhances ambiance, and so whether you are in a restaurant, theater or presentation space, you can create the environment that the lighting designer intended.
DIMMING OFFERS MANY OTHER BENEFITS:
• Space Flexibility: Dimming control systems provide for space flexibility. Your home and your workplace should be designed to complement your needs. As your needs change throughout the day, your lighting should adapt as well; bright to read a book, but dim for computer use. Whether you are at home or at work, lighting control can create a comfortable atmosphere to support your activities throughout the day.
• Enhanced Safety: Lighting controls can enhance the safety and security of your home. You can control both interior and exterior lights from the car as you approach your driveway to ensure optimal visibility and can even connect to security systems to turn on lights in case of an emergency.
• Increased Productivity: Lighting control also increases productivity allowing the user to select the level he/she needs to reduce eye strain and fatigue so that they can work at peak performance for more of the day, or so students can concentrate better and learn more at home or at school.
MEASURED LIGHT AND PERCEIVED LIGHT
To understand the performance of dimming LED we have to know the difference between measured light output and perceived light output.
Measured light: Measured light output is the quantifiable value of light measured by a light meter or similar device. This is the dimming percentage indicated on LED product specification sheets.
Perceived light: Perceived light is the amount of light that your eye interprets because of pupil dilation. The eye’s pupil dilates at lower light levels, causing the amount of light to be perceived higher than measured (e.g., 20 percent measured light equals 45 percent perceived light). The equation for determining perceived light is to take the square root of the measured light percentage (e.g. √0.2 = 0.45).
You need to select the dimming range of your fixture or lamp that will be suitable for your application. A product that dims to 20 percent measured light (45 percent perceived) wouldn’t make sense in a media room, but may be the energy-saving solution necessary for an office
LED PRODUCT AND DRIVERS
LEDs are low-voltage devices. Therefore, additional electronic components are typically required to convert the line-voltage power to a low voltage for the LEDs. These electronics may also interpret control signals, and dim the LEDs accordingly. These devices are referred to as LED drivers. LED luminaries come in two distinct types: the LED fixture and the LED bulb (also called an LEDi or retrofit lamp).
LED bulbshave Edison-base sockets and are meant to replace standard incandescent or screw-in CFL bulbs. The bases of these bulbs have integral drivers that determine if they are dimmable, and if so, what the dimming performance i
LED fixtures can vary from cove lights to down lights and usually have an external driver. Some fixture manufacturers offer different driver options on the same fixture to support different control technologies or applications (such as dimmable vs. non-dimmable).
There are two different types of drivers. LED drivers may be constant voltage types (usually 10V, 12V and 24V, etc.) or constant current types (350mA, 700mA and 1A, etc.).
Just as their names would suggest, a constant current driver provides a constant current, such as 700mA, to a pre-made LED array that is designed to operate at or below that current level. This is great for a down light, sconce or other LED fixtures that use only one light source per driver (much like a fluorescent lamp with its associated ballast).
A constant voltage driver provides a constant voltage to one or more LED arrays connected in parallel. A constant voltage driver is used in areas where you may have a variable amount of fixtures, such as a cove or under-cabinet light. Some drivers are manufactured to operate specific LED devices or arrays, while others can operate most commonly available LEDs. Additionally, the long-life benefits of LEDs would be reduced if the driver was not designed for an equally long life.
Dimming drivers can dim LEDs by Constant Current Reduction (CCR) or Pulse Width Modulation (PWM). Most dimming drivers operate using the PWM method. With this method, the frequency could range from a hundred modulations per second to thousands of modulations per second. The instantaneous response of LEDs to changing current makes them highly susceptible to flicker, especially compared to incandescent sources. One of the most important LED driver features to understand is the quality of the DC output voltage of the driver. Finally, be cautioned that remote mounting of the driver could result in potential voltage drops, power losses, or noise susceptibility on the DC wiring that must be properly accounted for.
CONCLUSION
Ten years ago, many people didn’t even know what an LED was. Today, they’re the new hot item. The rapid adoption of LED light sources is rooted in energy savings, long life, and new fixture options that enable them to use in almost any application. They are highly efficient; deliver a useful life-time averaging 50,000 hours; and offer very good color rendering. LED lamps also emits very little infrared(IR) radiation and contain no mercury. Despite those clear advantages, issues of compatibility between LED lamps, drivers, and controls continue to cause confusion for specifiers and their customers. If they are paired improperly performance will suffer.
Data source: IEEE papers on LED , www.lutron.com, LED Magazine etc.