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  • Benefits and drawbacks of LEDs

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    LEDs offer a huge variety of benefits but at the same time they cannot be viewed as the optimum solution for every lighting-related application. Here, in no particular order, we list some of the main advantages of LEDs, together with some of the challenges faced by these devices.
    By Tim Whitaker - the Editor of LEDs Magazine.

    Lifetime
    As solid-state light sources, LEDs have very long lifetimes and are generally very robust. While incandescent bulbs may have an expected lifetime (to failure) of 1000 hours, LEDs are often quoted of having a lifetime of up to 100,000 hours - more than 11 years. However, this figure is extremely misleading; like all other light sources, the performance of LEDs degrades over time, and this degradation is strongly affected by factors such as operating current and temperature.
    At present, there is no standard definition of lifetime for LEDs, although various parties have suggested that lifetime should be the time taken for the LED’s output to fall to some percentage (such as 70% or 50%) of its original value.

    Standardization
    The general lack of standardization in the LED field is an ongoing issue. Various standards relating to LEDs exist in areas such as automotive lighting and traffic signals. Other efforts are being conducted by bodies such as CIE, NEMA and IES.

    Low maintenance
    The long lifetime of LEDs reduces the need to replace failed lamps, and this can lead to significant savings, particularly in the cost of sending out maintenance crews. This also makes LED fixtures useful for installation in relatively inaccessible locations. However, if tasks like cleaning the light fixture or performing electrical checks need to be carried out regularly, then the light sources could be replaced at the same time, negating the "low maintenance" advantage.

    Efficiency
    LEDs are high-efficiency light sources. White LEDs with efficacies of 25 lm/W and up are commercially available, exceeding the performance of incandescent and some fluorescent sources. The directional nature of light produced by LEDs allows the design of luminaires with higher overall efficiency.

    Low power consumption
    The low power consumption of LEDs leads to significant energy savings that can often drive the installation of LED-based systems, for example traffic signals. National programs to develop effective solid-state lighting industries in the US and Japan have been driven by the potential energy savings associated with using LEDs.

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    Brightness
    Although LEDs have high efficiency and consume a small amount of power, the devices produce a small total number of lumens. For example, a 60 W incandescent bulb with an efficiency of 20 lm/W produces 1200 lumens. A one-watt LED with an efficiency of 30 lm/W produces only 30 lumens i.e. 40 such LEDs are required to produce the same amount of light as the incandescent bulb.

    Heat
    LEDs don't produce heat in the form of infrared radiation, which makes incandescent bulbs hot to the touch. The absence of IR radiation allows LED fixtures to be positioned in locations where heating from conventional sources would cause a particular problem e.g. illuminating food or textiles.
    However, LEDs do produce heat at the semiconductor junction within the device. The wall-plug efficiency (optical power out divided by electrical power in) of LED packages is typically in the region of 5-40%, meaning that somewhere between 60 and 95% of the input power is lost as heat.
    Without very efficient thermal management and heat sinking this causes the junction temperature of the LED to rise, which causes the LED characteristics to change. Driving LEDs above their rated current causes the junction temperature to rise to levels where permanent damage may occur.

    Cost
    In many applications, LEDs are expensive compared with other light sources, when measured by metrics such as “dollars-per-lumen”. LED manufacturers continue to work towards reducing their production costs while at the same time increasing the light output of their devices.
    However, the high initial cost of LED-based systems is offset by lower energy consumption, lower maintenance costs and other factors.

    Small form-factors
    LEDs are very small - typical high-brightness LED chips measure 0.3 mm by 0.3 mm, while high-power devices can be 1 mm x 1 mm or larger. There are many examples where the availability of small, high-brightness devices have enabled significant market advancement. The obvious example is in mobile phone handsets, where blue, green and white LEDs are now used in most models to backlight keypads and liquid-crystal display (LCD) screens.

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    Instantaneous switch-on
    LEDs switch on rapidly, even when cold, and this is a particular advantage for certain applications such as vehicle brake lights.

    Color
    LEDs are available in a broad range of brilliant, saturated colors (although performance varies across the spectrum), and white devices are also available. Modules containing different-colored LEDs (typically red, green and blue, or RGB) can be tuned to a huge range of colors, and easily dimmed. RGB modules provide a much wider gamut of colors than white LEDs or other traditional white light sources, which is a particular advantage in applications such as backlighting liquid-crystal displays (LCDs).

    RGB LEDs and color mixing
    LED characteristics change with time, temperature and current, and from device to device. For RGB LEDs, the performance of different-colored devices changes at different rates. This can result in variation of lamp color and intensity, and poor reproducibility.

    White LEDs
    The color of white LEDs can be very inconsistent, although manufacturers have narrowed their binning ranges. White LEDs with the same correlated color temperature can have different color tints perceptible to the human eye.

    Semiconductor processing
    Fabricating LEDs is a complex high-temperature process involving the growth of crystalline layers across the surface of a semiconductor wafer. The quality of these layers determines the properties of the LED. Reproducibility is difficult to achieve across a single wafer, or from wafer to wafer, or from day to day. Some LEDs processed from a wafer will yield high quality devices, while others from the same wafer will have much lower quality and will end up in low-end applications such as children's toys.

    Designability
    LEDs open up many new design options, some of which were previously inconceivable.

    Environmental
    LEDs do not contain mercury and in many cases steps are being taken to replace lead-containing solders (used mainly to fix LEDs to circuit boards) with lead-free material, in line with European directives. The energy-efficient nature of LEDs also makes them environmentally friendly.

    Drivers
    LEDs are low-voltage light sources, generally requiring a constant DC voltage or current to operate optimally. Designing and implementing an effective driver is key to obtain all the benefits of LEDs.

    Knowledge gap
    In general, there is a gap in understanding between the LED manufacturers and the lighting community. The former group do not include the latter in their product development activities and do not provide information that is directly comparable to the information available for competing light sources. The latter do not understand a huge amount about LEDs and are unfamiliar with crucial issues such as thermal management, or why white LED performance is not highly consistent.

    [Source: LEDs Magazine]

  • What is OLED?

     

    OLED as of organic light-emitting diode, a display device that sandwiches carbon-based films between two charged electrodes, one a metallic cathode and one a transparent anode, usually being glass.

    The organic films consist of a hole-injection layer, a hole-transport layer, an emissive layer and an electron-transport layer.
    When voltage is applied to the OLED cell, the injected positive and negative charges recombine in the emissive layer and create electro luminescent light.

    Unlike LCDs, which require backlighting, OLED displays are emissive devices they emit light rather than modulate transmitted or reflected light.

    21c8niq

    OLED technology was invented by Eastman Kodak in the early 1980s. It is beginning to replace LCD technology in handheld devices such as PDAs and cellular phones because the technology is brighter, thinner, faster and lighter than LCDs, use less power, offer higher contrast and are cheaper to manufacture.

  • Too Much Blue Light Can Damage Your Eyes

    Blue light is important for the body to regulate the circadian rhythm, but too much exposure can cause permanent damage to the eyes, reported Pocono Record.

    The growing number of LED backlit devices emerging on the market ranging from smartphone screens, computer displays to tablet, are placing people at higher risks of experiencing retina and Age-Related Macular Degeneration (AMD).

    "It is when your eyes are exposed to the stronger blue light from light emitting diodes, or LEDs, you risk damage to the retina or macula," said Dr. John J. Glasner, co-owner of Eye Associates of Monroe County, Stroudsburg.

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          (Photo Courtesy of Reveiw of Optometry)

    The public’s exposure to blue light is expected to increase, as up to 90% of light sources will be replaced with LEDs, wrote Ronald Melton, adjunct faculty member at Indiana University School of Optometry and Salus University College of Optometry, in a Review of Optometry article in February 2014.

    According to Melton, LEDs and CFLs tend to emit a high level of blue light, in which LEDs contain a higher level of harmful blue light about 35% compared to CFLs 25%. The cooler the white LED the higher the blue light it emits.

    Blue light in the 415 nm to 455 nm has been identified by researchers as most harmful to the retina, while the 40 nm band of visible light caused the most retinal cell death. Blue light which is emitted by the sun combined with exposure to artificial LED light sources can cause accumulation of blue-violet light that over time can cause AMD.

    However, not all blue light is harmful. The blue-turquoise light range of 465 nm to 495 nm is essential for vision, and regulates our circadian biological clock and sleep/wake cycle.

    Studies have shown blue light from LEDs definitely affects the body’s circadian rhythms, said Dr. Michael Grandner, an instructor in psychiatry and a member of the Center for Sleep at the University of Pennsylvania

    To protect your eyesight, Glasner recommended limiting using computers, tablets, and smartphones before sleep time, adding people should dim the screen and keep it as far from the eyes as possible.

    People who work in front of a computer screen all day or for long hours should also consider using glasses tinted for reading LED screens, which mostly are in yellow or orange tings.

    Researchers at Rensselaer Polytechnic Institute also suggested limit time spent looking at smartphone screens to 10 minutes instead of three hours.

    Glasner also reminded people to research before buying glasses or filters, while some are able of blocking blue light not all are capable of doing so.

    Source: LEDinside.com

  • LED COB and MCOB package: The difference

    Most of the LED COB package by now, including Japan COB packaging technology, are based on inner substrate package, that is to integrated many chip encapsulated in one substrate, this is what we said COB technology. As we know under the substrate is copper foil, it a good conductive, but not good for optical processing.
    MCOB is different from COB, MCOB technology is place chip inside the optical cup directly, and it produced based on the optics, it’s not just one cup, but multiple cups, emitted lighting just concentrate inside the chip. In order to let more light emit out, it’s need a lot of angles, that means the more light outlet the better, and light efficiency will be improved, MCOB used in both lower and high power package.
    In any case, the efficiency of small-power encapsulation must be 15% greater than high-power packages, because the high power LED chip is large, and the light outlet area is only four, but the low power chip is divided into 16, than the light outlet area is 4 by 16 that is 64, so there are more light area. Anyhow we can improve the optical efficiency by 15%, MCOB use more light cups aim to improve the light efficiency, so finally have different light efficiency from COB.
    Mcob

  • What’s color temperature ?

    The color temperature is a light source color scale, the unit is K (Kelvin). Color temperature has important applications in the field of photography, video, publishing and so on. The color temperature of the light source is determined by comparing its colors with theoretical thermal blackbody radiation. When light source color match thermal blackbody radiation, then that Kelvin temperature is that the color temperature of the light source, which directly linked to the Planck’s blackbody radiation law.
    The color temperature is most universal indicator for the quality of the light source spectrum. Symbol Tc.

    Colour Temp

    The color temperature is to define by absolute blackbody radiation, when the light source radiation in the visible region identical with the absolute blackbody, then the temperature of the blackbody is the color temperature of the light source.
    The characteristic of low color temperature light source is more red radiation in the energy distribution, usually referred to as “warm light”. After the color temperature increases, there are more blue radiation in the energy distribution, high color temperature commonly referred to as “cold”. Some commonly used color temperature: standard candle is 1930K (Kelvin units), incandescent light is 2760-2900K, fluorescent 3000K, flashlight 3800K, sun at noon 5600K, electronic flash 6000K, blue sky 12000-18000K.

  • What’s lower power LED?

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    Usually, low power LED with rated current lower than 20mA, if higher current can be counted as high power LED. And recently most common used lower power LED is DIP and SMD. And they also have different types, here are the details:
    1) DIP LED (Light emitting diode): We have called LAMP LED, DIP LED also includes many types:
    By colloidal shape: 3mm, 4mm, 5mm, 8mm, 10mm, 12mm, square, oval, and there are also some special sharps;
    By color: red, orange, yellow, green yellow, green, blue green, blue, pink, UV, white, infrared, etc.
    DIP LED
    2) SMD LED (Surface mount device): surface mount diodes or surface mount components are its name; SMD also has a variety of types:
    By size: there are 2020, 3528, 3535, 5050, 0603, 0805, 1210, 5060, 1010 and so on. Generally, SMD are diamond-shaped, so its name is based on the size L * W, most SMD use inches for units, only a few are used millimeters, such as 1608 (1.6 * 0.8mm) and so on. The color and colloid are the similar to DIP LED, only the shape of the product is different.

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    SMD LED
    Low power LED advantages:
    It is with small size, good for lighting design with small space; and even color; also good for radiate heating.
    Low power LED disadvantages:
    Low brightness and light efficiency; high light attenuation; usually one lamp need several LED, poor stability.
    Application range:
    Usually used as back light source for TV, mobile phone, card light etc; and LED display also need thousands of lower power LED, some companies even used in LED lamps.

  • What’s the high power LED?

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    Generally, high-power LED light source is a single LED power higher than 0.5W. At present, many manufacturers use low power LED, but it need use a lot of LED, and also lower power LED with higher light decay. So its trend to use high power LED source in commercial lighting.
    High power LED is a light emitting diode with high rated current. Low LED power is generally 0.1W, operating current is 20mA, but high power LED can reach 1W, 2W, or even tens of watts, operating current can be range from tens of mA to several hundred mA. Due to the constraints of flux conversion efficiency and cost, it decides high-power mainly used in some special lighting areas in short-term, and long-term goal is the general lighting.
    High power LED advantages:
    High-power LED as the light source with features of low power consumption, less heating, long life, fast response, good direction and so on. Housing is available for PC pipe, able to bear high temperature of 135 degrees, low temperature of -45 degrees.
    High power LED disadvantages:
    Current high-power LED light conversion efficiency is still low, and cost is high. White LED color is easy to be changed for long time use, cooling.
    Application range:
    High-power LED mainly used in oilfield, petrochemical, railway, mining, military and other special industries. And most important is high power LED is more and more popular in general lighting.
    LED EXPRESS's photo.

  • How to calculate LED display brightness ?

    LED display now become very popular product for the outside advertising, event, shows and so on, and there are many people don’t know how to calculate the brightness, here give detail information for the calculation. Let’s take P12mm outdoor 1R1G1B DIP346 for example, total pixels is 6944/m2, and scan module 1/2.

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    And before calculation, we need know the brightness of each LED, this can be supplied by the package companies, we take the following list for example:
    Color Red Green Blue
    Original brightness 1000 mcd 2100 mcd 400 mcd
    Ratio 30% 60% 10%
    All with 10% 1000/3=333 mcd 2100/6=350 mcd 400/1=400 mcd
    P12mm LED display with 1R1G1B, so the original brightness for each pixel is:
    1x1000mcd+1x2100mcd+1x400mcd=3500mcd=3.5cd
    But the original brightness is not with R:G:B=3:6:1, so it’s not in white balance. And now we need to adjust the LED brightness with 3:6:1 ratio, this ratio means: red take 30% of total brightness, blue take 60%, and Blue take 10%.
    Color Red Green Blue
    All with 10% 1000/3=333 mcd 2100/6=350 mcd 400/1=400 mcd
    Adjust brightness 10%=333 mcd 10%=333 mcd 10%=333 mcd
    White Balance 30%=1000 mcd 60%=2000 mcd 10%=333 mcd
    Pixel brightness One pixel in total: 1000+2000+333=3333mcd=3.333cd
    Sq.m brightness One squre meter in total: 3.333×6944=23144cd
    1/2 scan 23144/2=11572cd/m2
    20% loss 11572×80%=9257.6cd/m2

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    When in 10% brightness:
    Red 333mcd So we calculate based on red brightness, and cut the green and blue color, and meet the ratio:R:G:B=3:6:1. And the one pixel brightness is: 3.333cd, for P12mm with 6944 pixels each square meter, so the brightness is 23144/m2, also for P12mm LED screen, when in 1/2 scan, the brightness is also 1/2, that 11572cd/m2, and this is just theoretical value, there will be about 20% loss when use, so the final brightness is 9257.6cd/m2, or 9257.6 nit.
    So, did you got how to calculate the brightness finally ?

  • How to choose a good LED display ?

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    Now, LED display is very popular for the advertising, TV studio, touring shows and so on. And many buyers may confused how to find a good quality and suitable screen, lednews.org will guide you step by step, and teach you how to choose a good LED display, and it’s mainly lies in the following aspects.
    1. Flatness: Display surface flatness need to within ±1mm, in order to ensure the display image is not distorted, partial raised or recessed will lead display dead viewing angle. The flatness mainly depends on the design and production process of both mask and cabinet.
    Flatness

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    2. Brightness: Usually, indoor full color brightness ≥800cd/m2, for outdoor full color display brightness ≥4000cd/m2, if outdoor against the sun, then much ≥6500cd/m2, otherwise it will be too low brightness to see the displayed image. The brightness is determined by LED and LED chip are used, and can be measured by luminance colorimeter.
    luminance colorimeter
    3. Viewing angle: Screen viewing angle directly determines the amount of audience, and of course the bigger the better. It’s mainly depending on the LED chip package. Usually, for SMD LED with angle of 120° (horizontal) and 120° (vertical), for DIP LED is 120°(horizontal) and 60° (vertical).
    Viewing angle

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    4. White balance: White balance is one of the most important indicators for LED display. In color science, it will show pure white color only when red, green and blue ratio meets 1:4.6:0.16. If the actual proportion is different, the white balance will have deviation. Generally pay attention to the LED screen whether there is bluish white or yellowish green color. White balance is affected by display control system and LED chip.
    white balance

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    5. Refresh rate: Refresh is a very important parameter for LED screen, especially in TV studio. If low refresh rate there will be scan lines in the image when the camera shoots on it, and the audience will see the flicker though the camera. Usually the refresh rate ≥1000Hz, some high standard application need 3000Hz or more.
    Refresh rate
    6. Color reduction: Color reduction refers to how the image color is produced by display, that means the LED screen color and video source must maintain highly consistent, so as to ensure that the image realism.
    color reduction

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    7. No mosaic and dead LED: Mosaic is square in the LED screen that always on or off, also means broken modules, mainly because broken cable or connector. Dead LED is the pixel in the display always on or off, and it’s mainly determined by LED chips are used.
    dead LED
    8. No color block: Color block is difference color between modules, the block mainly caused by signal transition between modules, this phenomenon is mainly depend on the control system, gray level, and scanning mode.
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  • LED light bulb advantages

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    LED light bulbs are considered the next generation lighting solutions as they provide environment-friendly illuminations and economical retrofitting solutions for existing buildings. In addition to providing long-term savings in energy bills, they provide better visibility and reduce maintenance needs.
    It is a natural trend to witness advancement and innovations in Science and Technology such that new inventions replace the status quo. In the light of this fact, the aspect of lighting system started with oil lamps, and gradually it turned into the era of candles, incandescent bulbs and LED bulbs.
    There are certain reasons for this technological metamorphosis, and these have to do with their limitations. Oil lamps and candles produce soot, and there is also emission of carbon dioxide with a trace amount of carbon monoxide (a toxic substance). Incandescent bulbs consume excessive energy. Compact fluorescent light bulbs (CFL) consume low energy, but it is not really an eco-friendly option as it may seem to be. CFL bulbs contain a small trace of mercury which is quite toxic to human life. If the bulb breaks, and any person comes in contact with the toxic substance, it will cause mercury poisoning.
    Today, a better option for lighting which most people now opt for is the use of LED light bulbs (light emitting diodes bulbs). They are safe and friendly to the human environment. A LED bulb has a number of advantages over other forms of lighting that could be used in a home or an office. Here are some of the advantages:
    1. Energy saving: The use of LED-powered bulbs is highly economical compared to other sources of lighting. The amount of energy required to power a LED lamp for a specific measure of luminosity (the brightness of light) is far below what is required in incandescent bulbs and in CFLs. LEDs save a great deal of energy. In fact, they are the best energy-saving bulbs. Using them in a home or in a working environment will drastically reduce the monthly energy bill.
    2. Long lifespan: LED lights generally have a lifespan of 10 years or more. By the time you might have used 10s of incandescent bulbs within the space of ten years, a user of a LED bulb may have to change it about 10 years later. It shows that a very little amount of money will be spent on the purchase of this lighting system.
    3. No lead and mercury: The absence of toxic substances such as mercury (which is found in CFL) makes LED lamps very safe to use anywhere. Once they get damaged, they can be disposed of with no need for extra scare, unlike CFL bulbs.

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    4. Light emitting diodes with solid state technology: As a result, the bulb can safely undergo an alternate on-and-off switching in millions of time without getting burnt. In fact, there is no filament that can burn, as it is in an incandescent bulb. It does not need to warm up before it lights up, as it is in the case of a compact fluorescent light bulb. So, switching on or switching off LED-powered bulbs is instant in effect.
    Moreover, LED lighting comes in various colors and they are gradually taking the place of CFLs. Their decreasing prices now encourage their use. There are big companies that are already using them as a way to cut down expenses on energy bill. All these things are indications that the usage of a LED light bulb is taking over as our best lighting system.

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