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LED Lights Selection Guide
LED Lights is a new solution way of lighting in the fulture. Compared with the traditional fluorescent lamp and incandescent bulbs,the LED Lights is much more advanced.Do you want to buy it,While you may be puzzled to choice.So here are some suggestion for you.
What is LED lights
A Light Emitting Diode (LED) is a semiconductor device which converts electricity into light. LED lighting has been around since the 1960s, but is just now beginning to appear in the residential market for space lighting. At first white LEDs were only possible by "rainbow" groups of three LEDs -- red, green, and blue -- by controlling the current to each to yield an overall white light. This changed in 1993 when Nichia created a blue indium gallium chip with a phosphor coating that is used to create the wave shift necessary to emit white light from a single diode. This process is much less expensive for the amount of light generated.
THE Feature of LED Lights
Advantages:
- Efficiency: LEDs produce more light per watt than incandescent bulbs.
- Color: LEDs can emit light of an intended color without the use of color filters that traditional lighting methods require. This is more efficient and can lower initial costs.
- Size: LEDs can be very small (smaller than 2 mm2) and are easily populated onto printed circuit boards.
- On/Off time: LEDs light up very quickly. A typical red indicator LED will achieve full brightness in microseconds.LEDs used in communications devices can have even faster response times.
- Cycling: LEDs are ideal for use in applications that are subject to frequent on-off cycling, unlike fluorescent lamps that burn out more quickly when cycled frequently, or HID lamps that require a long time before restarting.
- Dimming: LEDs can very easily be dimmed either by Pulse-width modulation or lowering the forward current.
- 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.
- Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt burn-out of incandescent bulbs.
- 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.
- Shock resistance: LEDs, being solid state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs which are fragile.
- 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.
- Toxicity: LEDs do not contain mercury, unlike fluorescent lamps.
Disadvantages:
- High initial price: LEDs are currently more expensive, price per lumen, on an initial capital cost basis, than most conventional lighting technologies. The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed. However, when considering the total cost of ownership (including energy and maintenance costs), LEDs far surpass incandescent or halogen sources and begin to threaten compact fluorescent lamps[citation needed].
- Temperature dependence: LED performance largely depends on the ambient temperature of the operating environment. Over-driving the LED in high ambient temperatures may result in overheating of the LED package, eventually leading to device failure. Adequate heat-sinking is required to maintain long life. This is especially important when considering automotive, medical, and military applications where the device must operate over a large range of temperatures, and is required to have a low failure rate.
- Voltage sensitivity: LEDs must be supplied with the voltage above the threshold and a current below the rating. This can involve series resistors or current-regulated power supplies.
- 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, due to metamerism, red surfaces being rendered particularly badly by typical phosphor based cool-white LEDs. However, the color rendering properties of common fluorescent lamps are often inferior to what is now available in state-of-art white LEDs.
- Area light source: LEDs do not approximate a “point source” of light, but rather a lambertian distribution. So LEDs are difficult to use in applications requiring a spherical light field. LEDs are not capable of providing divergence below a few degrees. This is contrasted with lasers, which can produce beams with divergences of 0.2 degrees or less.
- Blue Hazard: There is increasing 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.
- Blue pollution: Because cool-white LEDs (i.e., LEDs with high color temperature) emit much more blue light than conventional outdoor light sources such as high-pressure sodium lamps, the strong wavelength dependence of Rayleigh scattering means that cool-white LEDs can cause more light pollution than other light sources. It is therefore very important that cool-white LEDs are fully shielded when used outdoors. Compared to low-pressure sodium lamps, which emit at 589.3 nm, the 460 nm emission spike of cool-white and blue LEDs is scattered about 2.7 times more by the Earth's atmosphere. Cool-white LEDs should not be used for outdoor lighting near astronomical observatories.
The types of LED Lights :
The main types of LEDs are miniature, high power devices and custom designs such as alphanumeric or multi-color.
Miniature LEDs
These are mostly single-die LEDs used as indicators, and they come in various-sizes from 2 mm to 8 mm, through-hole and surface mount packages. They are usually simple in design, not requiring any separate cooling body.[45] Typical current ratings ranges from around 1 mA to above 20 mA. The small scale sets a natural upper boundary on power consumption due to heat caused by the high current density and need for heat sinking.
High power LEDs
High power LEDs (HPLED) can be driven at hundreds of mA to more than an ampere of current, compared with the tens of mA for other LEDs. They produce several hundred lumens. Since overheating is destructive, the HPLEDs must be mounted on a heat sink to allow for heat dissipation. If the heat from a HPLED is not removed, the device will burn out in seconds. A single HPLED can often replace an incandescent bulb in a flashlight, or be set in an array to form a powerful LED lamp.
Some well-known HPLED's in this category are the Lumileds Rebel Led, Osram Opto Semiconductors Golden Dragon and Cree X-lamp. As of September 2009 some HPLEDs manufactured by Cree Inc. now exceed 105 lm/W [46] (e.g. the XLamp XP-G LED chip emitting Cool White light) and are being sold in lamps intended to replace incandescent, halogen, and even fluorescent style lights as LEDs become more cost competitive.
LEDs have been developed by Seoul Semiconductor that can operate on AC power without the need for a DC converter. For each half cycle part of the LED emits light and part is dark, and this is reversed during the next half cycle. The efficacy of this type of HPLED is typically 40 lm/W.[47] A large number of LED elements in series may be able to operate directly from line voltage.
Offer LED Lights information and selection guide for you.
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