LEDs (light emitting diodes) are solid-state semiconductor devices that can convert electrical energy directly into light. The heart of a led is a semiconductor chip of which one side is attached on the top of an anvil that is the negative power lead, and the other side is connected with a whisker to a positive power lead. it is the most important part of the LED. and it is entirely encapsulated in an epoxy resin enclosure.
A semiconductor chip consists of two parts, one is called P- type semiconductor where holes dominate the region, and the other part is N-type semiconductor where is dominate by electrons. When they are sandwiched together, there is a PN junction in between. And when an electric current is applied to the chip through the lead, electrons are pushed across the junction into the P-region, there, electrons and holes meet and recombine, and then release energy in the form of photons of light. That is why LED can shine. And the wavelength of the light, therefore its color, depends on the materials forming the PN junction, which is, the materials used to make the LED chip.
Generally, LED chips are made from gallium-based crystals that contain one or more additional materials such as phosphor to produce a distinct color.
The Development of LED
Since the first practical visible-spectrum LED was developed in 1962, the development of LED has attained to such a high level that LED has been widely chosen as the best alternative to incandescent bulb, neon and fluorescent light in many area. And it is predicted that with the further development of LED. the above-mentioned light sources would entirely give way to LED in the near future. And the future of the human being will be brighter since the common use of LED would save us a lot of energy, money, and time.
The development of LED can be roughly divided into three steps, which are the advent of red light lED, and then blue light Led, and white light LED. Red light and green light Led have been developed for decades, but they are all monochromatic LED, if they were used as light sources, objects illuminated would all wear the color emitted from the monochromatic LED, instead of the inherent color of the objects, so their applications are limited. The ultimate aim of LED development is super-bright white light LED that can actually replace the conventional light sources. lt has been a long and hard way to go until Shuji Nakamura, a Japanese scientist, managed to make a blue light LED from gallium nitride in 1993. lt turned out to be a crucial breakthrough in the development of LED. Based on the technology of blue light LED, a white light LED was soon invented in 1997,From then on, LED products have been widely used in many areas, and regarded as the light source of future.
Features and Benefits of LED
The inherent features of LED is decidedly the ability of LED to become the best alternative to conventional light sources, and provide a wider range of applications.
Small Size
An LED is essentially a microscopic chip once encapsulated in an epoxy resin are extremely small and lightweight.
Low power consumption
LED consume very little power, far less than standard light bulbs leading to greatly reduced energy costs and extremely enhanced global energy savings. LEDs also require far less energy to manufacture than other light sources, reducing the environmental impact of artificial lighting even further. Generally a LED is designed to operate at 2 - 3.6V, 0.02-0.03A current which means a LED typically requires no more than 0.1W to operate.
Rugged
LEDs are rugged, solid state devices and are not susceptible to vibration such as with incandescent filament based bulbs.
Long Lifetime
When operating at specified voltage, current, and within specified environmental conditions, LEDs can enjoy a long life of up to 100,000 hours. A newer way to evaluate LED lifetime has been established and adopted by Neo-Neon which is based on lumens depreciation over time to determine the Mean Time between Failure (MTBF).
High Luminous Efficiency and Low heat Emitting
Due to the special materials that are used to manufacture LEDs during electrons transition, LED’s mainly emit electromagnetic energy in the visible parts of spectrum. This is unlike incandescent fi laments which are heated and emit large amounts of electromagnetic energy in the infrared spectrum which can’t be seen and is felt as heat. That is to say, LEDs can convert significantly more of the energy applied into light, and therefore LEDs have a higher luminous efficiency with substantially lower amounts of heat produced.
Environmental Protection
LEDs are made from non-toxic materials, unlike fluorescent lights that contain mercury which poses a danger to the environment and human health.
LEDs are recyclable.
Unbreakable
The LED semi-conductor chip is completely embedded in an epoxy resin enclosure which is much more sturdy than traditional glass bulbs and fluorescent tubes. They are solid-state technology thus no loose and moving parts which makes LEDs virtually indestructible.
The application of LED
LEDs proprietary characteristics mentioned above determines their ideal suitability to be applied in a wide range of products and applications.
Decorative Lighting
Due to the rich variety in colors, compact size, durability, energy savings, and long life LEDs are a perfect light source for decorative application. Mounted on a PCB, flexible PCB, cable wire, or other electrically conductive materials LEDs are versatile and are being applied to the entire range of decorative lighting.
General and Commercial Illumination
With the advance of the WLED (White LED) technology applied singularly, in clusters, or arrays are now bright enough to be used for General and Commercial Illumination. Homes, Offices, Public Buildings, Shopping Centers, and alike, all around the world are applying new WLED based illumination products.
Display
Indoor and Outdoor Visual display systems are rapidly becoming the mainstay of the display and signage industry. The affordability of LED based screens and displays are also rapidly becoming more cost effective through a variety of designs, resolutions, and varied pixel pitch. The largest LED display in the world is 36m high located in Times Square, Manhattan, U.S.A.
LCD Backlight
Because of LEDs compact size, durability, energy savings, long life, and low power consumption, LEDs are perfect light sources for LCD backlight displays.
Color
The advancement of LED technology and color control systems have brought about a very broad spectrum of single, mixed RG, RB, GB, AWB (Amber White Blue) RGB, RGBY, Cool White, Warm White, and Ultra-Warm White. Varied combinations of varied blue wavelengths, blue green combinations, applied with various mixtures of phosphors have brought about a true rainbow of available colors.
Intensity, Beam angle, and Viewing angle
LED light output varies with the type of chip, encapsulation process, as well as other variables. Generally, the amount of light emitted from a LED is quantified by a single point, on-axis luminous intensity value (LV), and is specified in milli-candela (MCD). A LED with higher luminous intensity value does not mean that it has higher total light output. To measure the total light output, the viewing angle must be taken into account too. LED viewing angle is also a function of the LED chip type and the epoxy lens that distributes the light. LEDs with different chips and epoxy lens will have different viewing angles. lf two LEDs have the same luminous intensity value, the lamp with the larger viewing angle will have the higher total light output.
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