LED Knowledge
LED LIGHT F&Q
1. Question: what is an LED?
Answer: a light emitting diode (LED) is a semiconductor device that emits visible light when electrical current passes through it, it is a special kind of diode.
2. Question: what color of light can LED emit?
Answer: most LEDs are monochromatic. Light color is associated with the light wavelength. LEDs made with different semiconductor materials emit lights in different wavelengths. LED light wavelengths range from 400 nanometers (blue) to 800 nanometers (red). The colors of popularly available LEDs in the market are red, orange, amber, yellow, green, blue and white.
3. Question: Can LEDs be used to replace conventional incandescent and florescent light bulbs?
Answer: yes and no. LEDs have increasingly been used in many different applications to replace old incandescent light bulbs. Examples include LED indicator lights for all kinds of electronic devices such as cell phone, calculators, automotive dash panel, LCD back-lighting, etc., LED seasonal decoration lights for Christmas and holidays, LED traffic signs and other LED direction signs, LED flashing lights, and so on. As currently available LEDs have limited brightness, in most cases, they can not be used to replace incandescent or florescent light bulbs for general lighting purposes.
4. Question: what are the advantages of LEDs compared with conventional incandescent lights?
Answer: there are several obvious advantages LEDs have over traditional incandescent light bulbs, they are as follows:
Low power consumption - energy saving,
Long lasting,
Cold lighting,
Ruggedness,
Small size and weight,
Fast switch times,
Simple to use.
5. Question: could you give more detailed explanations about these LED advantages?
Yes. Currently available LEDs are more energy efficient than incandescent bulbs, but less than florescent bulbs with the same light output. The power consumption of popular LEDs ranges from 30mW to 200 mW.
People can save money & energy by using LEDs instead of equivalent incandescent decorative bulbs.
The rated average working life of LED is 100,000 hours compared with 1,000 hours of incandescent bulbs.
LEDs emit cold lights as working LEDs generate very small amount of heat, so LEDs are much safer than equivalent incandescent light bulbs in terms of danger of fire. LEDs don’t have filaments to heat up in order to emit lights just like the case of incandescent bulbs. Lights are emitted from LEDs as a result of energy exchange occurring in the different semiconductor materials an LED is made of.
LEDs are usually shielded with solid transparent plastic materials so they are more rugged than incandescent and florescent bulbs that are usually sealed with glass.
LEDs can be powered by either AC voltage or DC voltage. The circuit that is required to appropriately drive LEDs is much simpler than that for florescent bulbs.
6. Question: we have seen so many advantages LEDs have over incandescent light and florescent bulbs, are there any disadvantages LEDs exhibit compared with incandescent or florescent bulbs?
Yes, the most significant disadvantage is the light output limitation of LED. Currently available LEDs emit limited amount of lights at a relatively small angle range, while incandescent and florescent light bulbs illuminate in all directions and give out much more brightness of light. And this is the reason why LEDs currently can not be used for general lighting applications.
The second significant disadvantage is the high prices of LEDs. The currently available LEDs in the market are 3 ~ 10 times more expensive than equivalent incandescent light bulbs. This is why some customers still hesitate to buy LED products even though LEDs have so many obvious advantages over incandescent bulbs and people actually can save money by using LED products in the long run.
7. Question: what LED products are currently available for general customers?
Answer: the most popular LED products available in volume at the market place are various kinds of LED decoration light products. And in fact, they are ideal for replacing conventional incandescent decoration light products, because when compared with incandescent light products, these LED products save up to 95% energy, have much longer working hours, are more rugged, and safer in terms of danger of fire and electric shock.
At present, people can buy beautiful LED light strings, LED rope lights, LED icicle strings, and individual round LED bulbs with changeable colors, LED rope lights, LED pipe lights, and more other LED products will be put into market in the near future.
8. Question: as we notice that in LED light strings, LEDs are in series connection just like incandescent light strings, how do you compare these two kinds of light strings in terms of reliability?
Answer: LEDs are more reliable. Most available LED light strings have series configuration like old incandescent light strings, where lights in the string are connected in series with each other, so a disconnection of LED light from the string will always make the entire string fail just like incandescent light strings. However, in the case of light burning, an incandescent light bulb will always burn open, namely, the filament of the incandescent bulb breaks, so the whole string will always fail, while an LED light may either burn open like an incandescent light bulb or burn short where a short circuit is formed inside the LED, so the burned LED will stop lighting but all the rest LEDs in the string still light normally. And LEDs usually burn short, therefore, LEDs are more reliable than incandescent light bulbs in that respect.
9. Question: are there any LED strings better than those in series connection?
Answer: yes, there is. Various LED string products are more reliable than those LED strings in series connection in market. OUR strings use a unique patented connection configuration that ensures an LED string will work normally even one or several LEDs are disconnected from the string while keeping the low prices and all the features of LED strings.
10. Question: why are LEDs of some colors are more expensive than LEDs of other colors?
Answer: the reason is that different semiconductor materials are used for different color LEDs, and some semiconductor materials are more expensive than others; another reason is that manufacturing costs are different. White LEDs are the most expensive because red, green and blue LEDs are combined together to make a white LED.
What is LED ?
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).
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 higherluminous 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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