LED Lighting Operation and Benefits
By Stephen Ethier (Editor EnergyTrace.com and Member of the Illuminating Engineering Society)
Light emitting diodes, commonly called LEDs, are becoming more and more widespread in all uses from small flashlights to laptops, cellular phones, and televisions. You may think they are a new invention but they have been in commercial use since the 1970s as replacements for incandescent and neon indicator lights on electronic equipment. It has only been recently that LED manufacturing has reached a point where LEDs can be used to replace conventional lighting such as incandescent and fluorescent bulbs.
Before we discuss the benefits of LEDs, let’s review how LEDs operate. LEDs differ from conventional light sources in the manner in which they produce light. Incandescent lamps are composed of a tungsten filament surrounded by a glass bulb filled with an inert gas. The tungsten filament is heated by electric current until it glows and emits light. On the other hand, fluorescent lamps are composed of a glass tube coated in phosphor and a very small amount of mercury. An electric arc excites the mercury atoms, which emit ultraviolet (UV) radiation. When the UV rays strike the phosphor coating, they are converted and emitted as visible light.
An LED is essentially an electronic component referred to as a solid state device. When used in lighting, it is referred to as SSL (Solid State Lighting). It is composed of crystalline layers of semiconducting materials to form what is called a p-n (positive- negative) junction. The one-directional travel of electrons and electron holes flow into the junction between the semiconducting materials and combine to release energy in the form of photons. Depending on the semiconducting materials, the emitting light can be invisible or in the visible spectrum of radiation. Red LEDs are based on aluminum gallium arsenide (AlGaAs), blue LEDs are made from indium gallium nitride (InGaN) and green from aluminum gallium phosphide (AlGaP). The components are covered in an epoxy lens.
Since “white” light is necessary for most lighting applications and LED’s do not initially produce white light, a method of generating white light had to be developed.
The first method uses Red, Green and, Blue LEDs to form multiple LED chips sometimes referred to as an RGB-LED . By mixing multiple wavelengths of different LEDs, an approximation of “white” light is emitted. By the use of a controller, combinations of wavelength intensities can create a multitude of colors allowing the designer to adjust the white light to a specific color temperature. However, because of the use of three LEDs for each chip, this type of chip is often more expensive to manufacture.
The second method uses a single blue Indium-Gallium-Nitride (InGaN) LED with a yellow phosphor coating to create white light. This is the method that results in the more commonly seen “white LED”. The low cost and sufficient performance makes it the most widely used technology for general LED lighting today. The disadvantage is the inability to dynamically change the character of the light and the fact that phosphor conversion reduces the efficiency of the device.
LEDs come in two different basic categories, low power and high power. Low power LEDs are typically 0.1 watt, low current (~20 milliamps) and low voltage (3.2 volts DC). This type is used as indicators due to the small output of light, around 2 to 4 lumens. High power LEDs are manufactured in 1 to 3 watt packages, high current (350-1000 milliamps) and currently maximum 138 lumens per watt and are the type used for lighting. Compare this to a 100 watt incandescent bulb at 17 lumens per watt, a 32 watt T8 fluorescent at 85 to 95 lumens per watt, or a compact fluorescent at 48 to 60 lumens per watt.
Because the light output of individual light-emitting diodes is small compared to incandescent and compact fluorescent lamps, multiple diodes are typically arranged in arrays to achieve the desired light (lumen) output.
With some units, the LED array is an integral part of the luminaire/fixture, unlike an incandescent light source where you replace the bulb when it fails. There are several reasons why the LED array is part of the fixture. The main reason is heat dissipation. The fixture is designed in conjunction with the LED array to properly dissipate the heat generated by the many individual LED chips. LEDs lose their efficiency if allowed to heat up.
There has also been the introduction of the LED Module System made of the LED modules, power supply and control interface modules. This allows for a building block approach to create a variety of lighting patterns. There are now commercial LED lamps that are designed to replace incandescent quartz halogen lamps such as MR and PAR and fluorescent T8 36w lamps in existing installations without the need to replace the fixture.
From learning about the operation of LEDs you probably have realized the various benefits of using LEDs for a lighting source. So, to help solidify your thoughts on LEDS, here are excerpts from two energy reports giving you some percentages of savings.
According to the ICT for Energy Efficiency report compiled by the Ad-Hoc Advisory Group (European Commission) composed of Information and Communications Technologies providers, industry associations, end-users including regional and city groups as well as leading academics:
“Solid-state light sources, i.e. light-emitting diodes (LED) and organic light emitting diodes (OLED), may in the future outperform almost all other light sources in terms of efficiency and thus provide a saving potential of about 50% of the electrical energy used for lighting. If the advanced LED technology is combined with intelligent light management systems, which will control the light output according to ambient lighting conditions or people’s presence, another 20% can be saved – in sum 70%.”
But it doesn’t end there with the tremendous energy efficiency of the LED’s. There are also environmental aspects that need to be mentioned. The ability to direct the light from LED fixtures toward the desired area reduces light pollution. As well, LEDs do not contain mercury, lead, or glass.
In January of 2011, the DOE (US Department of Energy) released a report that targets the use of LED lighting in 12 specific product types spread over three general categories: general illumination, outdoor lighting, and consumer electronic displays. For general illumination applications, four markets were analyzed: PAR, BR, and R-shaped; MR16; 2-foot by 2-foot troffer fixtures; and general service A-type. For outdoor lighting, four markets were analyzed: roadway, parking, area and flood, and residential. DOE also analyzed four applications for consumer electronic displays: televisions, laptops, monitors, and mobile handsets.
The report indicates that converting to LED-based light sources could approach an estimated annual saving of 263 terawatt-hours. This is the equivalent of taking 21 million households off the power grid. The DOE SSL 2010 Multi-Year Program Plan predicts that commercial LED luminaire efficacy will increase 155% over the next decade to 219 lumens per watt (lm/W). Assuming that the LED replacements within each niche improve according to the DOE’s SSL 2010 Multi-Year Program Plan predictions for 2020, LED efficacy increases the total potential energy savings dramatically to 399 TWh. This equates to a forecasted primary energy savings of the total energy required to power nearly 32 million average U.S. households.
According to the DOE report, the advantages other than just energy savings include: longer operating life, reduced radiated heat, minimal light loss, dimmability and controllability, durability, enhanced performance at low temperatures, safety improvements, smaller package size, uniform illumination, mercury reduction, enhanced product appearance, improved color rendition, and lower lumen depreciation.
Now, let’s summarize the advantages of LEDs as well as the disadvantages.
Advantages of LEDs
Disadvantages of LEDs
There is no doubt that the use of LEDs for lighting applications has the great potential to save energy and allow for new and inventive lighting methods. They will not replace traditional methods such as incandescent and fluorescent overnight but they are evolving into a strong contender.