A light emitting diode (LED) is a semiconductor device that emits light when an electric current is passed therethrough. Improvement in the quality of artificial illumination is nowadays a top priority requirement. Advances in LED technology have triggered the development of LEDs with a satisfactorily high light output, which makes them an appealing alternative to incandescent or fluorescent lamps. LED lighting systems come to be more ubiquitous as replacements for present lighting systems. LEDs feature a plethora of unique attributes which may make them the perfect choice for some lighting applications. The special characteristics covered in this guideline include: Energy Efficiency; Controllability; Directionality; Small Size; Durability; Cold temperature operation; Instant-on/ Rapid cycling; Negligible IR and UV emissions; Extended Life; Environmental impact.
Incandescent or filament-based lamps are extremely inefficient light sources, with up to a whopping 95% of the input energy lost, mostly in the form of heat or infrared energy. While a fluorescent lamp that yields as much useful visible light energy may require just one-third to one-quarter as much power. LEDs are solid state devices that convert electric energy to light and typically consist of one or more active regions of semiconductor material interposed amid oppositely doped semiconductor layers. An LED circuit will get closer to 80% efficiency, which implies 80% of the electrical energy is converted to light energy; the rest of the 20% is lost as heat energy. The economics of lighting has three key variables--light (lumens, lm), power (watt, W), and cost (dollar, $). Luminous efficacy is the amount of light emitted per unit of electrical power (lm/W). For reference, incandescent lamps have a luminous efficacy of approximately 8-15 lm/W. A fluorescent lamp is significantly better at somewhere around up to 85 lumens/Watt. Today's white LEDs, at around 160 lumens/Watt, have luminous efficacies that are undoubtedly superior to those of incandescent lamps. Aside from that, it is believed possible to raise the luminous efficacies of LEDs up to 200-300 lumens/Watt, with additional improvements in the underlying materials and device properties and design.
Not only the LEDs can be combined in red-blue-green arrays which can be regulated to produce almost any color light. With effectively designed electronic control systems, LED luminaires can be controlled for color balance and intensity at the same time maintaining color fidelity. Lighting control systems can be applied to LED lightings for a massive space, including lightings on the exterior walls of a building, or lighting systems for concerts. The DALI standard, let's say, makes it possible for a digital communication lighting control system capable of satisfying a variety of user needs by allocating addresses to different combinations of lighting scenes. This is simply not commonly attainable with conventional light sources. Compared to incandescent lamps and fluorescent lamps, LED lighting has an excellent dimming capability. In other words, dimming an LED light source does not reduce the life span of the LED light source. Thus, as the cost of LED lighting goes down, LED lighting is becoming the lighting of choice for numerous applications.
LED-based luminaires are highly directional by nature. LED devices are flat and emit light from a single side. An LED is fundamentally a Lambertian source in which the light intensity varies around with the cosine of the angle away from the LED surface normal. They characteristically emits in a directional Lambertian spatial intensity distribution having intensity that fluctuates with cos(?) in the range ?=[0°, 90°] and has zero intensity for ?>90°. Incandescent, halogen, and fluorescent lamps are generally omni-directional light sources. Omnidirectional lamps usually are meant to produce substantially uniform intensity distribution as opposed to angle in the far field, more than 1 meter away from the lamp. But nevertheless, a great deal of the light produced by the lamp can be wasted within the fixture, reabsorbed by the lamp, or escapes from the fixture in a direction that is not a good choice for the intended application. As a result of directional nature of their light output, LEDs potentially have higher application efficiency than other light sources in a number of lighting applications. This intensity distribution strongly elevates light intensity in the forward direction, making the LED a highly directional light source, trimming the need for reflectors and other optical elements that can trap light. The direct nature of LEDs can bring about efficiencies of 80% to 90%. This ends up with reduced maintenance costs by eradicating or practically reducing the frequency of required maintenance. Therefore, well-designed fixtures and systems using LEDs can potentially produce illumination more efficiently to the intended location.
Conventional light sources are generally bulky, problematic to integrate, and are inclined to result in increased size in optical systems that utilize them. LED lamps works extremely well in a very flexible manner owing to their exceptionally small dimensions. LED lighting modules are very small in size. The compactness of LED modules makes it possible for lighting designers to make light sources into shapes and sizes suited for numerous applications. Although LEDs by nature operate on direct current (DC) and need a driver to convert alternating current into a suitable direct current for the LED. Electronic circuitries employed to drive the LEDs are becoming tremendously compact and for that reason can be incorporated in many different compact fixture designs.
Incandescent light bulb packages comprise a light source made up of an incandescent filament within a glass enclosure. Fluorescent tubes have tube-shape shells manufactured from transparent, fragile material such as thin glass. Nevertheless, the filaments and glass encloures are fragile. LED characteristics do not change drastically with age and they are not easily broken by shock or vibration. LEDs are solid-state devices without any moving parts. LEDs are generally formed as dies having an anode terminal and a cathode terminal. The LED die and optional substrate are subsequently packaged and soldered to a printed circuit board (PCB). There is nothing to break, rupture, and shatter. This makes LED lighting systems extremely reliable and offers added value in applications where broken lamps present a hazard to occupants.
Instant-on/ Rapid Cycling
The LED is an instant on, instant off light source without any re-strike delay, as opposed to the longer warm-up and response times involved with fluorescent lighting. Mercury and sodium vapor lamps both exhibit seriously slow starting times, often measured by many minutes. The optical output of the LED light sources in LED lighting systems changes rapidly with changes to the electrical input. and are well suited for use in applications that are subject to frequent on-off cycling, in contrast to fluorescent lamps that burn out more quickly when cycled frequently.
The manufacturing of LED systems are environmentally safe and recyclable since they don't make use of mercury or other hazardous materials. Fluorescent lamps contain mercury and phosphors which can be hazardous materials and will need special disposal to prevent environmental problems. Fluorescent tubes have tube-shape shells built from transparent, fragile material such as thin glass, and further have harmful materials including mercury vapor filled in the shells. As soon as the fluorescent tubes were broken, mercury or mercury vapor would leak out instantly from fluorescent tubes to cause an atmospheric pollution or a terrible damage to ambient people. Even very small amounts of mercury are adequate to pollute a property. Thus, both the manufacture and disposal of mercury-containing fluorescent tubes is hazardous. Accordingly, fluorescent tubes have a great hidden trouble and are in high risk of resulting in damage to both people and environment directly. LEDs contain no mercury, and LED products can be manufactured without lead solder, simplifying their end of life disposal.
LED lighting systems can offer a long operational lifetime when compared with conventional incandescent and fluorescent bulbs. Incandescent lamps typically have limited lifetimes (around 1,000 hours) as a consequence of high temperatures of the filaments, while fluorescent lamps have moderate lifetimes (around 10,000 hours) that are limited by the electrodes for the discharge. In contrast, LED lights are capable of operation for longer than 25,000 hours, and even as long as 100,000 hours or more.
Less Health Concerns
Typical LEDs produce negligible or no ultraviolet (UV) light and minimal infrared radiation (IR). Like incandescent light bulbs, LEDs come up with a certain amount of heat. Whereas incandescent light bulbs radiate a large amount of heat as infrared radiation when it comes to LEDs heat must primarily be dissipated by conduction and convection. Additionally, fluorescent lamps emit a tiny amount of ultraviolet (UV) light. UV light is unhealthy for humans, being the component that causes sun burns, so the UV component of the light is required to be converted into visible light. Unlike other light sources, LEDs manufactured for visible light illumination radiate a small amount of heat in the form of IR that may cause damage to sensitive objects or fabrics.
Cold Temperature operation
Fluorescent bulbs have significant performance variations across a wide range of temperatures. At some colder temperatures fluorescent bulbs do not operate at all. LEDs are solid state devices and its performance inherently improves as operating temperatures fall.