What is LED?
A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.
When a light-emitting diode is forward biased (switched on), 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 gap of the semiconductor.
An LED is often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern. LEDs present many advantages over incandescent light sources including lower energy consumption, longer life time, improved robustness, smaller size, faster switching, and greater durability and reliability. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output.
Light-emitting diodes are used in applications as diverse as replacements for aviation lighting, automotive lighting (particularly brake lamps, turn signals and indicators) as well as in traffic signals. The compact size, the possibility of narrow bandwidth, switching speed, and extreme reliability of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are also useful in advanced communications technology. Infrared LEDs are also used in the remote control units of many commercial products including televisions, DVD players, and other domestic appliances.
What's the main advantage of LED?
1.Efficiency:LEDs emit more light per watt than incandescent light bulbs. Their efficiency is not affected by shape and size, unlike fluorescent light bulbs or tubes.
2.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.
3.Size: LEDs can be very small (smaller than 2 mm2) and are easily populated onto printed circuit boards.
4.On/Off time: LEDs light up very quickly. A typical red indicator LED will achieve full brightness in under a microsecond.LEDs used in communications devices can have even faster response times.
5.Cycling:LEDs are ideal for uses subject to frequent on-off cycling, unlike fluorescent lamps that fail faster when cycled often, or HID lamps that require a long time before restarting.
6.Dimming: LEDs can very easily be dimmed either by pulse-width modulation or lowering the forward current.
7.Cool light:In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED.
8.Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt failure of incandescent bulbs.
9.Lifetime:LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. Fluorescent tubes typically are rated at about 10,000 to 15,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000–2,000 hours.
10.Shock resistance: LEDs, being solid state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs which are fragile.
11.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.
What's the LED general techical term?
Often used incorrectly with respect to illumination as a synonym for luminous flux, an objective measurement of the visible power of a light source. The term is correctly used when describing screen brightness in a display or television
A general expression for the effect of a light source on the color appearance of objects.
3.Color Rendering Index (CRI)
A measure of the degree of color shift objects undergo when illuminated by the light source as compared with those same objects when illuminated by a reference source of comparable color temperature. The reference source has a CRI of 100.
4.Color Spectrum / Visible Spectrum
The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye, typically between 390nm and 750nm.
The description used to describe the effect of heating an object until it glows incandescently, the emitted radiation, and apparent color, changes proportional to the temperature; easily envisioned when considering hot metal in a forge that glows red, then orange, and then white as the temperature increases.
6.Correlated Color Temperature (CCT)
The absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source. Usually specified in Kelvin (K). The lower the Kelvin temperature, the warmer the light feels, or appears.
7.Digital Addressable Lighting Interface (DALI)
A digital communications protocol for controlling and dimming lighting fixtures, originally developed in Europe.
8.Direct-View Lighting Fixtures
Lighting fixtures intended for viewing, rather than for illumination. For example, arrays of direct-view fixtures or nodes are used in large-scale video displays, traffic signals, and signage applications.
9.Directional Light Source
A light source that emits light only in the direction it is pointed or oriented.
A digital communications protocol for controlling lighting fixtures, originally developed to control stage lighting.
The light output of a light source divided by the total electrical power input to that source, expressed in lumens per watt (lm/W).
12.Flux / Luminous Flux
Luminous flux is the measure of the perceived power of light, adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light.
A widely accepted printed circuit board (PCB) material which is fiberglass reinforced epoxy laminates that are flame retardant.
An effect that occurs when lighting fixtures in the OFF state faintly glow as a result of residual voltage in the circuit.
A photometric device for testing the luminous intensity distribution, efficiency, and luminous flux of luminaires.
A part of the thermal system that conducts or converts heat away from sensitive components, such as LEDs and electronics.
17.High Power LED
A high power LED, sometimes referred to as a power LED, is one that is driven at a current of 350 mA or higher.
High-brightness is a term that is often applied to an LED but has no measured meaning and does not indicate any level of performance.
19.Hot / Cold Factor
The relative light output performance at a temperature compared to the light output at a nominal or test temperature. For LUXEON products this is the relative light output at 100C Tj compared to 25C Tj. For 'Hot Tested” products like LUXEON A it is the relative light output at 100C Tj compared to 85C Tj.
LED performance testing and specification at an elevated temperature of 85°C.
The intensity of light falling on a surface area. If the area is measured in square feet, the unit of illuminance is foot-candles (fc). If measured in square meters, the unit of illuminance is lux (lx).
22.Illuminating Engineering Society of North America (IES)
The recognized technical authority on illumination, communicating information on all aspects of good lighting practice to its members, to the lighting community, and to consumers through a variety of programs, publications, and services.
23.Inboard Power Integration
An approach to power management that integrates the power supply directly into a fixture’s circuitry, creating an efficient power stage that consolidates line voltage conversion and LED current regulation.
Electromagnetic radiation with wavelength range from 700 nm – 3000 nm.
A device used for a variety of optical, photometric, or radiometric measurements.
Junction temperature, noted as Tj, is the temperature of the LED’s active region.
Term and symbol (K) used to indicate the comparative color appearance of a light source when compared to a theoretical blackbody. Yellowish incandescent lamps are 3000K. Fluorescent light sources range from 3000K to 7500K and higher.
The international (SI) unit of luminous flux or quantity of light and equals the amount of light that is spread over a square foot of surface by one candle power when all parts of the surface are exactly one foot from the light source. For example, a dinner candle provides about 12 lumens.
Describes the percentage of light lost relative to the initial lumen output. See lumen maintenance for more information.
The luminous flux at a give time in the life of the LED. This is expressed as a percentage of the initial luminous flux.
31.Lumen Maintenance Curve
A graph illustrating the predicted average light output behavior over time of a single LED or solution.
The total lumens emitted of a light source, system, or solution.
A lighting fixture complete with installed lamps and other accessories.
The percentage of total lamp lumens that a lighting fixture, luminaries, or system emits, minus any blocked or wasted light.
The SI (International) unit of luminance, or luminous flux incident on a unit area, frequently defined as one lumen per square meter (lm/m2).
The active power divided by the apparent power (i.e., product of the input voltage and input current of a driver).
37.Power Factor Correction
In an electronic device, such as an LED lighting fixture, a system of inductors, capacitors, or voltage converters to adjust the power factor of electronic devices toward the ideal power factor of 1.0.
38.Pulse Width Modulation (PWM)
A method, used by LED drivers, to regulate the amount of energy to the LEDs. PWM turns LEDs on and off at high frequency, reducing total ON time to achieve a desired dimming level.
A description of the devices that do not contain moving parts or parts that can break, rupture, shatter, leak or contaminate the environment.
40.Thermal Resistance (K/W)
The property of a material's ability to conduct heat.
Electromagnetic radiation with wavelength shorter than that of visible light.
The amount of light a lighting fixture delivers in an application, minus any wasted light.
How many kind of LED packaging method?
What are the going great advantages of white LED?
At present, white LED function lighting is mainly LED streetlight, LED tunnel light, LED tube light. Compared with traditional lighting, white LED light source in the application process shows many advantages. In the next few years, the next generation of white LED lighting will become the main product.
White LED as a semiconductor light source, compared to traditional lighting sources, and its power consumption is only about 20% of the latter. With white LED light source, will reduce to a conventional semiconductor light-emitting energy consumption about 20% of lighting.
Details are as below:
1.Long life span. More than 30,000hrs, 5 times longer than traditional lighting products.
2.High lighting efficacy and color rendering index. Luminous efficiency is more than 100lm/w, narrow light spectrum, high CRI.
3.Easy installation. Especially for tube light, no need to remove starter, install directly in lighting fitting.
4.Low heat productivity. Within 50°in summer for temperature control, also can adopt passive heat dissipation.
5.Low maintenance cost. Compared with traditional lighting products, the maintenance cost is low. For modularization, when partial failure will not affect whole lamp working.
6.Energy saving. More than 50% energy saving compared with traditional lighting fixture.
7.High safety. Safe voltage (low voltage) to drive, stable lighting, no stroboscopic and ultraviolet radiation damage.
8.Start immediately. LED reflects immediately; ensure multi light connecting and different area changing at the same LED. When using dedicated driver to supply power, the start time is less than 10ms;
9.No light pollution. Directional light of LED is helpful for controlling distribution of light, to ensure ideal lighting effect. At the same time, eliminate LED glare, light pollution and improve the using of LED lighting efficiency greatly.
10.Low light decay. Integrated design of lighting fixture is avoid of reduplicate waste of light; The color temperature is adjustable to meet different requirements to have a comfortable feeling.
11.Green initiative. No lead, mercury and other harmful element, very friendly to environmental, no UV-light pollution.
As mentioned above, there are so many advantages of white LED, LED lighting was called third revolution in human lighting history. At present, all over the world is seeking for solution of the contradiction between economic development and energy shortage, seeking for the way of human being and environment harmonious development. As known to us all, semiconductor illumination industry will generate great investment opportunity.
In China, illumination is 12% in total electricity consumption. LED lamps are energy saving, environmental protection, long lifespan, maintenance-free, easy to control and so on. In terms of saving energy, reducing greenhouse gas emissions point of view, or from the perspective of reducing environmental pollution, LED light source as a new choice to traditional lighting sources have great potential. The same as transistors replaced electronic valve, semiconductor light alternative to traditional incandescent and fluorescent lamps in general lighting will cause a revolution.