LED Light working Process & Its Pros and Cons
1. Introduction
LED (Light Emitting Diode) is a small light emitting device that comes under “active” semiconductor of electronic components. It is quite comparable to the normal general-purpose diode, with the only big difference being its capability to emit light in different colors. The two terminals (anode and cathode) of a LED when connected to a voltage source in the correct polarity may produce lights of different colors, as per the semiconductor substance used inside it.
Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike incandescent bulbs, they don't have filaments that burn out, they use less electricity, and they don't get especially hot. They're illuminated solely by the movement of electrons in a semiconductor material, and they last just as long as a standard transistor. The life span of an LED surpasses the short life of an incandescent bulb by thousands of hours
Until the mid-90s LEDs had a limited range of colors, and in particular commercial blue and white LEDs did not exist. The development of LEDs based on the gallium nitride (GaN) material system completed the palette of colors and opened up many new applications.
2. Working Process
A light-emitting diode is a two-lead semiconductor light source. It is a p–n junction diode that emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor. Detail working process is given below:
- The material used in LEDs is basically aluminum-gallium-arsenide (AlGaAs). In its original state, the atoms of this material are strongly bonded. Without free electrons, conduction of electricity becomes impossible here.
- By adding an impurity, which is known as doping, extra atoms are introduced, effectively disturbing the balance of the material.
- These impurities in the form of additional atoms are able either to provide free electrons (N-type) into the system or suck out some of the already existing electrons from the atoms (P-Type) creating “holes” in the atomic orbits. In both ways the material is rendered more conductive. Thus in the influence of an electric current in N-type of material, the electrons are able to travel from anode (positive) to the cathode (negative) and vice versa in the P-type of material. Due to the virtue of the semiconductor property, current will never travel in opposite directions in the respective cases.
- From the above explanation, it’s clear that the intensity of light emitted from a source (LED in this case) will depend on the energy level of the emitted photons which in turn will depend on the energy released by the electrons jumping in between the atomic orbits of the semiconductor material.
- We know that to make an electron shoot from lower orbital to higher orbital its energy level is required to be lifted. Conversely, if the electrons are made to fall from the higher to the lower orbitals, logically energy should be released in the process.
- In LEDs, the above phenomena is well exploited. In response to the P-type of doping, electrons in LEDs move by falling from the higher orbitals to the lower ones releasing energy in the form of photons i.e. light. The farther these orbitals are apart from each other, the greater the intensity of the emitted light.
Different wavelengths involved in the process determine the different colors produced from the LEDs. Hence, light emitted by the device depends on the type of semiconductor material used.
Infrared light is produced by using Gallium Arsenide (GaAs) as a semiconductor. Red or yellow light is produced by using Gallium-Arsenide-Phosphorus (GaAsP) as a semiconductor. Red or green light is produced by using Gallium-Phosphorus (GaP) as a semiconductor.
3. Pros and Cons
Pros
1. Energy efficiency: LED lights use about 50 percent less electricity than traditional incandescent, fluorescent and halogen options, resulting in substantial energy cost savings, especially for spaces with lights that are on for extended periods. These lights are up to 80% more efficient than traditional lighting such as fluorescent and incandescent lights.
2. Lighting Efficiency: LEDs emit more lumens per watt than incandescent light bulbs. The efficiency of LED lighting fixtures is not affected by shape and size, unlike fluorescent light bulbs or tubes.
3. Extended life: Unlike incandescent lighting, LEDs don’t “burn out” or fail, they merely dim over time. Quality LEDs have an expected lifespan of 30,000–50,000 hours or even longer, depending on the quality of the lamp or fixture. A typical incandescent bulb lasts only about 1,000 hours; a comparable compact fluorescent lasts 8,000 to 10,000 hours.
4. Cold temperature operation: LEDs love the cold unlike fluorescent lamps. At low temperatures, higher voltage is required to start fluorescent lamps, and luminous flux (the perceived power or intensity of light) is decreased. In contrast, LED performance increases as operating temperatures drop.
5. Durability: Traditional lighting is usually contained in a glass or quartz exterior, which can be susceptible to damage. LEDs, on the other hand, tend not to use any glass, instead they are mounted on a circuit board and connected with soldered leads that can be vulnerable to direct impact.
6. Instant on: Most fluorescent and HID lamps do not provide full brightness the moment they’re switched on, with many requiring three minutes or more to reach maximum light output. LEDs come on at 100-percent brightness almost instantly. The response time is very less – only about 10 nanoseconds.
7. Controllability: It can take more than a few dollars to make commercial fluorescent lighting systems dimmable, but LEDs, as semiconductor devices, are inherently compatible with controls. Some LEDs can even be dimmed to 10 percent of light output while most fluorescent lights only reach about 30 percent of full brightness. LEDs also offer continuous, opposed to step-level, dimming.
8. No IR or UV Emissions: Less than 10 percent of the power used by incandescent lamps is actually converted to visible light; the majority of the power is converted into infrared (IR) or radiated heat. Excessive heat and ultraviolet radiation (UV) presents a burn hazard to people and materials. LEDs emit virtually no IR or UV. Rapid advancements in LED lighting technologies, with more improvements on the horizon, have resulted in lowered costs and increased reliability of LEDs.
9. Low voltage require: Very low voltage and current are enough to drive the LED. Voltage range – 1 to 2 volts. Current – 5 to 20 milliamperes.
10. Color: LEDs can emit light of an intended color without using any color filters as traditional lighting methods need. This is more efficient and can lower initial costs
11. Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt failure of incandescent bulbs.
12. Shock resistance: LEDs, being solid-state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs, which are fragile.
13. Focus: The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner. For larger LED packages total internal reflection (TIR) lenses are often used to the same effect.
14. Light weight and can be small size: Miniature in size and hence lightweight. LEDs can be very small (smaller than 2 mm2) and are easily attached to printed circuit boards.
Cons
1. Efficiency droop: The efficiency of LEDs decreases as the electric current increases. Heating also increases with higher currents which compromises the lifetime of the LED. These effects put practical limits on the current through an LED in high power applications.
2. Light quality: Most cool-white LEDs have spectra that differ significantly from a black body radiator like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under cool-white LED illumination than sunlight or incandescent sources.
3. High initial price: LEDs are currently more expensive (price per lumen) on an initial capital cost basis, than most conventional lighting technologies. As of 2012, the cost per thousand lumens (kilolumen) was about $6. The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed.
4. Temperature dependence: LED performance largely depends on the ambient temperature of the operating environment – or "thermal management" properties. Over-driving an LED in high ambient temperatures may result in overheating the LED package, eventually leading to device failure. An adequate heat sink is needed to maintain long life. Toshiba has produced LEDs with an operating temperature range of -40 to 100 °C, which suits the LEDs for both indoor and outdoor use in applications.
5. Use in winter conditions: Since they do not give off much heat in comparison to traditional electrical lights, LED lights used for traffic control can have snow obscuring them, leading to accidents.
6. Electrical polarity: Unlike incandescent light bulbs, which illuminate regardless of the electrical polarity, LEDs will only light with correct electrical polarity. To automatically match source polarity to LED devices, rectifiers can be used.
7. Area light source: Single LEDs do not approximate a point source of light giving a spherical light distribution, but rather a lambertiandistribution. So LEDs are difficult to apply to uses needing a spherical light field; however, different fields of light can be manipulated by the application of different optics or "lenses". LEDs cannot provide divergence below a few degrees. In contrast, lasers can emit beams with divergences of 0.2 degrees or less.
8. Impact on insects: LEDs are much more attractive to insects than sodium-vapor lights, so much so that there has been speculative concern about the possibility of disruption to food webs.
9. Voltage sensitivity: LEDs must be supplied with the voltage above the threshold and a current below the rating. Current and lifetime change greatly with a small change in applied voltage. A slight excess of voltage or current can damage the device.
10. Blue hazard: There is a concern that blue LEDs and cool-white LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ANSI/IESNA RP-27.1–05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems.
11. Studies reveal that light emitted by LEDs can cause retinal changes, if there is high exposure for even a short period.
4. Conclusion
LED lights are made up of small diodes. Each diode is created from semiconductor material. This difference in electron levels allows electrons to move from one layer to the next, creating light through electronic excitation.
LEDs have swept the conventional lighting marketplace for a variety of reasons, most notably their extended lifespans, reduced energy consumption and lower maintenance requirements. By 2030, the DOE estimates that LED lighting could save 190 terawatt hours of electricity per year, which equates to a whopping $15 billion. As the purchase price of lamps and fixtures continues to fall, more and more facility managers are looking to upgrade their lighting systems with LEDs, given their many benefits compared to traditional technologies.
References:
1. https://www.toppr.com/bytes/principles-of-led/
2. https://www.gecurrent.com/ideas/8-advantages-of-led-lighting
3. https://www.linkedin.com/pulse/advantages-disadvantages-led-lucas-du/
5. https://electronics.howstuffworks.com/led.htm