LED retrofit lamps have started to show up on retail shelves. Many players in the LED industry are giddy about the anticipated growth over the next few years. Nevertheless, the road to success for LED lighting will not be completely smooth, as there are a number of pitfalls to navigate.
Bumps in the road ahead for solid-state lighting article gives a picture of the expected pitfalls. Some of the potential problems ahead are pricing, color quality, thermal management, regulatory, and consumer education. While most of these issues are not technical, the design engineer will nonetheless need to understand them.
While white LEDs are very efficient light sources, converting approximately one-third of the input power into light, the remaining two-thirds is converted into heat in the LED. Currently impossible to passively cool an LED that outputs 1,500 lm (the typical output of a 100-W light bulb) in the physical confines of the normal light bulb size form factor. So at 100 lm/W, about 10 W must be continuously and rapidly dissipated while keeping the LED well below maximum operating temperature (typically approximately 120ºC).
Thermal management will get somewhat easier in the future. As LED efficiencies improve, the thermal management improves by approximately the square of the efficiency, because the total power supplied to the LED decreases and the percentage of heat generated by that input power also decreases by the same amount.
Color quality may be the most difficult problem to solve. The industry has spent tremendous time and expense in measuring and controlling the color variability of white LEDs. But color temperature and tight chromaticity binning don’t tell the complete story, because two light sources with identical chromaticity coordinates may have very different wavelength spectra. LED spectrum is very different from the incandescent’s spectrum. If the spectra are too different, non-white surfaces will appear to be different colors under the two light sources. The Color Rendering Index or CRI is a measure of how closely the perceived color of a surface illuminated by a particular light source will be to the perceived color of the same surface under incandescent illumination. A CRI of 100 is a perfect match. A CRI above 80 for an LED is considered good.
In the short term, LED retrofit bulbs will make the initial splash, but in the long term there are great opportunities for custom LED luminaires. LEDs make possible much more complex form factors and consequently can create more interesting and useable illumination patterns than traditional bulbs and CFLs. Imagine a luminaire that not only is dimmable, but one that you can select the color temperature you desire.
When LED efficiencies reach the 150 lm/W range, it will become feasible to increase office lighting to 1,000 lux, as opposed to the 300 lux now typical in most office spaces.
To Protect LEDs, Know Your Standards
http://www.designnews.com/author.asp?section_id=1386&doc_id=256265
Light-emitting diodes (LEDs) have become so prominent in so short a time that new standards and specifications are emerging faster than most engineers can gain familiarity with them. Prime among those are standards involving overcurrent and overvoltage protection from such organizations as the International Electrotechnical Commission (IEC), the Institute of Electrical and Electronics Engineers (IEEE), Underwriters Laboratories (UL), and the US Department of Energy’s Municipal Solid State Street Lighting Consortium (MSSSLC), among others.
The Future in Automotive Front Lighting
http://www.designnews.com/author.asp?section_id=1365&doc_id=256391&cid=NL_Newsletters+-+DN+Daily
the non-incandescent solutions require power electronics to regulate light output. Ultimately, the article predicted a move toward a completely LED-based two-stage electronics design.
This two-stage converter (a single boost stage followed by multiple independent buck stages) was shown to have the most flexibility and scalability while providing the best performance. Though it is fairly easy to describe the benefits of LED-based headlights versus incandescent or HID, the nuances of one LED driver topology versus another are less obvious. To better understand the merits of a two-stage design, the single-stage solutions must be examined in more detail.
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The market has pulled a record number of dangerous electrical equipment. Finnish Safety and Chemicals Agency’s control in the attacks was caught almost 260 items. Very many of them were LED light.
Poor equipment design have been found in a lot, especially in LED light bulbs.
- With high enthusiasm we went to the new technology and then forgotten the basic electrical engineering, grant Hannu Mattila.
The majority of those who reject the decision device is derived from the Asian countries. Similarly, there are also quality equipment, as electronics production has shifted to Asia almost completely. The European Union as required CE marking can be found in the quality of products, but also in bad products.
CE marking is not in itself guarantee that the product is safe for sure.
Source: http://yle.fi/uutiset/hehkulamput_havitettiin_sahkoiskun_vaara_tuli_tilalle/6440515
Linear and switcher LED supplies combine, overcome disadvantages of each topology
http://www.edn.com/design/led/4404595/Linear-and-switcher-LED-supplies-combine–overcome-disadvantages-of-each-topology
To control their brightness, LEDs need a constant current; this can be done with a resistor placed in series with the LED string. Both the LED-string voltage and the supply voltage can vary, so a dedicated LED driver is a must to guarantee the current accuracy. Two solutions—each with advantages and disadvantages—are widely used: a linear constant-current LED driver or a step-down switching converter.
In spite of the additional components, the combined linear/buck solution is valuable in applications where low-noise performance and the extended supply-voltage range are desirable. Linear-to-buck transition voltages can be set to optimize the thermal dissipation.
Correction Technique Adds ‘Warmth’ to Dimmable LED Light
http://www.designnews.com/author.asp?section_id=1395&doc_id=257274&cid=NL_Newsletters+-+DN+Daily
Engineers at NXP Semiconductors say they’ve found a way to take the “coldness” out of dimmable white light-emitting diode (LED) light.
Using a combination of new technologies that earned the company 15 patents, the company’s engineers can reportedly remove the harshness from white LEDs and replace it with the “warmer” combination of yellow and white that’s familiar to consumers
“LED lights have always had this cold white — a hospital white,” Radu Sudeanu, senior scientist for NXP, told Design News. “But now we know how to correct it to get the right color.”
With its new technology, NXP hopes to make LEDs acceptable to a broader swath of consumers. In the past, some retailers have reportedly received dimmable white LEDs back from unhappy customers, some of whom say the light is too much like that of a fluorescent bulb. “Many people don’t like it,” Surdeanu told us. “They want the same yellowish light that we’ve all grown accustomed to for a hundred years with the Edison bulb, and for a thousand years before that with fire.”
NXP engineers remove “coldness” from LED light with a three-pronged solution. By combining the black body radiation curve (which relates light wavelength to light intensity) of an incandescent bulb with a logarithmically-based dimming technique, and then correcting for temperature variation, they say they can produce a color that lies between amber and white.
First driver compatibility program for LED modules
http://www.edn.com/electronics-products/other/4405003/First-driver-compatibility-program-for-LED-modules?cid=EDNToday
The Driver Compatibility Program for LED products provides LED lighting manufacturers with a list of driers compatible with Cree LED modules, based on evaluation and testing by Cree. Leveraging the technology and features of third-party drivers, the program enables lighting manufacturers to quickly address unique requirements in various countries, and differentiate their products.
The program, previously limited to the use of Cree drivers with Cree products, extends Cree’s LED module warranty to the use of Cree’s LED module with a compatible third-party LED driver.
Light an LED without wasting energy
http://www.edn.com/design/led/4369638/Light-an-LED-without-wasting-energy
LEDs need current to illuminate, and current usually flows through a power supply to an LED. A typical LED-driver circuit uses a transistor to provide current and a series resistor to decrease the voltage you apply to the LED. Unfortunately, the energy (VSOURCE−VDIODE)×IDIODE in a transistor/resistor combination goes to waste, giving off heat.
minimize this waste by using an inductor and an oscillating circuit to control the current through the LED
This circuit provides a general way of saving power without worrying about the intensity issues or operating voltage of the device.
You can expect efficiencies as high as 80% with this circuit.
You can use a 5- to 10-mH ferrite-core inductor for L1 with a white LED with a forward-voltage drop of approximately 3V.
Dimming LEDs with pulse-width modulation
http://www.eetimes.com/design/smart-energy-design/4405792/Dimming-LEDs-with-pulse-width-modulation
LEDs can be dimmed in two ways: analog and pulse-width modulation (PWM) dimming. Analog dimming changes LED light output by simply adjusting the DC current in the string, while PWM dimming achieves the same effect by varying the duty cycle of a constant current in the string to effectively change the average current in the string. Despite its attractive simplicity, analog dimming is inappropriate for many applications.
Analog dimming is inappropriate for many applications because it loses dimming accuracy by about 25 percent+ at only 10:1 brightness levels, and it skews the color of the LEDs. In contrast, PWM dimming can produce 3000:1 and higher dimming ratios (at 100Hz) without any significant loss of accuracy, and no change in LED color.
World’s most energy efficient light bulb
NanoLight surpasses standard fluorescents and LEDs
http://www.electronicproducts.com/Optoelectronics/LEDs/World_s_most_energy_efficient_light_bulb.aspx
It may look a little funny, but NanoLight is used to the stares. The futuristic-looking light bulb has an unconventional look big enough to match its unique energy-efficiency.
The bulbs look a bit like a three-dimensional jigsaw puzzle, all sharp corners and seams, because that’s essentially what they are: several small circuit boards with LEDs connected that are cut to fit together. The loose, interconnected design allows the bulb to dissipate more heat than a standard bulb while also directing light in all directions.
Currently, NanoLight comes in 10W and 12W bulbs. While the 10W uses 50% less energy than a compact fluorescent bulb with the same light output, the 12W is NanoLight’s breakthrough product. The bulb generates more than 1600 lumens, equivalent to a 100W incandescent light bulb. That works out to a little more than 133 lumens per watt — about 200% more efficient than other light bulbs on the market.
The project almost immediately surpassed its $20,000 goal on Kickstarter with more than 2,000 backers pledging over $100,000.
LED dimming adjusts to circadian rhythm
http://www.edn.com/electronics-products/other/4406362/LED-dimming-adjusts-to-circadian-rhythm
Warm Glow Dimming and Color Curve Dimming LED technologies adjust and change color temperatures throughout the day to improve the user’s performance and comfort by stabilizing their circadian rhythm.
Steampunker extraordinaire [Jake von Slatt] loves the idea of solar-powered garden lights soaking up the sun’s rays during the day and powering a LED in the evening. Commercially available solar lanterns, as [Jake], you, me, and everyone else on the planet have discovered, are universally terrible and either don’t have solar panels large enough to charge a battery, or only last a year or so.
Source: http://hackaday.com/2013/02/13/a-table-saw-to-cut-solar-panels/
Pairing LEDs with dimmers: The ground rules
Tips on making your LED bulbs dimmable
http://www.electronicproducts.com/Optoelectronics/LEDs/Pairing_LEDs_with_dimmers_The_ground_rules.aspx
you’ve decided to replace all your bulbs with LEDs and connect them to dimmer circuits for extra home ambiance. Unfortunately, the pairing of LEDs and a dimmer circuit is not that simple, and you must meet a number of factors to ensure proper dimming.
Pick a dimmer designed for LED
Verify LED labeling: Purchasing LED-compatible dimmers is not enough, the LED itself must be labeled by the manufacturer as being dimmable in the first place; otherwise the LED will not perform properly.
Compare light output: Recall that LEDs are energy efficient; therefore, a 16 to 20-watt LED is equivalent to a 100-watt incandescent bulb in terms of light produced. Rather than focusing on wattage when selecting the LED bulb, pay attention to lumens
Match the base shape
The bottom line: The most important thing to remember when pairing your LED bulbs with dimmer switches is that the two must be compatible. Failing to install the right switch will produce inadequate dimming.
Get more operating life from LED-based bulbs
http://www.edn.com/design/led/4410231/Get-more-operating-life-from-LED-based-bulbs-
Replacing incandescent lighting mandated by the largest countries around the world is powering a paradigm shift to solid-state lighting.
While a traditional incandescent bulb has a life expectancy of 1000 hours(1), LED bulbs offer the promise of up to 50,000(2) hours of operating time, while consuming only approximately 20% of the power for equivalent light output. But without the right precautions, the lofty promise of nearly 25 years without changing a light bulb may fall short.
The complexity and reliability of the driver circuit compatibility with legacy dimmer technology and the LEDs themselves are areas of concern that need to be addressed in order to maximize operating life.
The legacy LED driver technology previously available for LED bulbs required large numbers of external components, costly isolation components and special design considerations to avoid long-term degrading of key components (such as electrolytic capacitors) when interacting with dimmers, commonly used in homes across the world.
The integration of the driver circuit inside the bulb now makes the bulb susceptible to reliability issues, such as infant mortality or degraded MTTF (mean time to failure) rates.
Since the driver circuit transforms a high AC-voltage (100VAC/220VAC) down to a DC voltage that can be used to power the LEDs, electrical isolation is necessary for safety reasons.
primary-side digital control technology that allows for sensing of the LED current via the primary side of the isolation transformer using real-time waveform analysis. This eliminates the need for direct feedback from the output
By reducing the external components count and eliminating the opto-isolator (the component with the highest FIT rate), the reliability of the LED driver circuit goes up, improving the overall reliability of the entire bulb.
The LED driver needs to manage several factors to support the dimmer function, including dimmer detection, compatibility and light flicker.
When a dimmer is used to control the brightness of an A-lamp, the resulting load on the dimmer is also purely resistive and the current through the dimmer is constant and controlled.
An LED driver is effectively a current source and its input looks highly capacitive to the dimmer, which on start-up will see a large spike of in-rush current
An elegant solution to the dimmer in-rush problem is to use a two-step approach to driving the LEDs.
The digital control block that provides the primary-side control also contains algorithms for detecting and operating with virtually all dimmers available in the market
One method to ensure long operating life is to de-rate the current driving the LED and simply use more LEDs to generate a specific light output, resulting in less heat generation per LED and therefore a lower junction temperature.
A second method is to optimize the maximum LED current then establish a desired maximum junction temperature at which the LEDs current needs to be reduced in order to prevent degradation.
In the event that the maximum programmed temperature threshold is reached, the controller reduces the LED current by 10% increments until the temperature stabilizes.
fail-safe mode where the current through the LEDs reduces to 1% of programmed output current
This over temperature protection (OTP) topology offers flexibility in the design of the LED bulb and peace of mind that the bulb will be fully protected under extreme operating conditions.
Switching from CCFL to LED backlighting
http://www.electronicproducts.com/Optoelectronics/LEDs/Switching_from_CCFL_to_LED_backlighting.aspx
Here are some options available for liquid crystal display backlighting
There are currently four options for backlighting a display: (1) continue to use CCFLs with dc/ac inverters for as long as parts are available, (2) make an easy switch to an LED driver using a number of options currently on the market such as kits and drop-ins, (3) choose an LED driver, standard or newly designed, for an LED display that does not come with an onboard driver, and (4) for the display that has an onboard driver, it is possible to use the system’s existing input power signals and convert the analog dimming signal used for the inverter into a PWM signal for the LED driver.
CCFL still hanging on
CCFLs are not entirely dead yet, and they are still an option for certain legacy applications (for example, medical and point-of-sale) where a re-design for LED backlighting is not yet necessary or economical.
The majority of LCD users, however, are switching to LED backlights.
If you are sourcing a driver for an LED backlit LCD, you have a few options that can make the switch surprisingly fast and easy.
One option is a development kit available for OEM LED-backlit LCDs that includes everything necessary to get the panel, backlight and driver fully operational.
For CCFL designs already in the field, it’s possible to swap an LED rail for the CCFL lamp, or tube. LED rails are available on a long, narrow PC board that fits into a metal channel or “rail” that is similar in form factor to the channel in which CCFLs are commonly fitted. These are available as a drop-in replacement
There are many standard LED drivers available on the market today. However, LED backlights create new challenges for the power supply driving the BLU, challenges that cannot be met by the many single-chip ICs currently available. Getting optimum performance from LED BLUs requires a full-function power supply,
Another option is to integrate an LED display into an existing design by providing interconnectivity from the existing controller or power supply to the LCD backlight driver.
Ensure long lifetimes from electrolytic capacitors: A case study in LED light bulbs
http://www.edn.com/design/analog/4411475/Ensure-long-lifetimes-from-electrolytic-capacitors–A-case-study-in-LED-light-bulbs
Hot LEDs and short-lived electrolytic capacitors
Several years ago I worked on a few designs for LED light bulbs. Very early on it became clear that the temperatures of components in such light bulbs can get quite high. I personally measured component temperatures as high as +130°C in light bulbs purchased at local retail stores. Now admittedly, these were early LED bulb designs. Manufacturers now understand that, even though these LED bulbs consume substantially lower power than those they would replace, they still must have good thermal engineering. This is the only way to get the lifetime of the electronics to match the lifetime of the LEDs themselves.
I found it disturbing that many of these hot designs contained electrolytic capacitors which are notorious for a short lifetime at elevated temperatures. I expected that the lifetimes of these capacitors would severely compromise the lifetime of the products, and not allow them to reach the 30,000 to 50,000 hour capability of the LEDs themselves. With common electrolytics rated at 2,000 to 5,000 hours at +85°C, I vowed not to use an electrolytic in any LED bulb designs.
In talking to LED bulb manufacturers at that time I found that many did not understand the limitations of electrolytic capacitors.
It is important to understand both the “endurance” spec of electrolytic capacitors and how temperature affects it.
Conversely, lifetime decreases by a factor of 2 for every +10°C increase in temperature. Therefore, at +100°C, the endurance of the 2,000 hour, +105°C-rated capacitor mentioned above would be 21/2 x 2000, or about 2800 hours. Even if you assume that, on average, the capacitor operates at +95°C, its lifetime only increases to 4000 hours. This is hardly the 30,000 to 50,000 hours desired for LED light bulbs.
Power factor and ripple: a trade-off
The more cost-effective LED light bulb designs back in those years all utilized single stages. All of the single-stage architectures of which I am aware produce either good power factor or low-output 120Hz (100HZ) ripple. Not both…unless you use at least one large-valued capacitor. To get capacitor values large enough to allow a design to deliver both, electrolytics must be used.
As time passed LED bulb manufacturers have become more sophisticated and low ripple is now desired. A good solution involves two-stage designs with a front-end power factor correction (PFC) circuit followed by a separate regulator, typically a fly-back.
We built a couple of prototypes and placed a much lower-valued ceramic capacitor right at the output and our larger electrolytic further away where it was not near the heat-generating components.
It was also important to examine the reduction in capacitance over the time that the endurance spec implied.
This is a good example of the importance of fully understanding the details of component specifications.
Will new lighting technology save energy?
http://www.electronicproducts.com/Optoelectronics/LEDs/Will_new_lighting_technology_save_energy.aspx
Lighting needs are said to use about 20% of our global energy production. So the use of CFL and LEDs can lead to fewer coal-fired power plants and that directly reduces the amount of CO2 released into the atmosphere, which is good for the atmosphere.
The U.S. Energy Information Administration says that in 2011 about 461 billion kWh of electricity were used for lighting by residential and commercial sectors, which equaled about 12% of total U.S. electricity consumption
A simplistic comparison states that the LED has a life-span of 50,000 h vs 1,200 h for incandescent bulbs (and 8,000 h for CFLs). Additionally, an incandescent bulb producing the typical 800 lumens requires 60-W of power while a CFL uses 13 to 15 W, and an LED lamp needs only 6 to 8 W. For example, the environmental impact (CO2 emissions) of 30 incandescent bulbs (4500 lbs CO2/year) is about 10X more than the same number of LED bulbs (451 lbs/year). These are promising numbers if the comparison holds up.
Gadget Freak Case #239: Bridge Rectifier Eliminates LED Light Flicker
http://www.designnews.com/author.asp?section_id=1362&doc_id=262542&dfpPParams=bid_30,aid_262542&dfpLayout=blog
When I converted my holiday lights from incandescent mini-lights to LEDs, my wife and daughter did not want them in the house. That was a surprise. They’re both visual people, and I thought they would like the vivid colors of the LEDs. At first, they did, but soon they complained the flickering LEDs gave them headaches. Eventually, I noticed the flicker and knew the cause: 60Hz line power. Even if you cannot see the flicker, your eyes might detect it — with ill effect.
By rectifying the AC line power with a full-wave bridge rectifier and using its output to power the strings, I eliminated the flicker.
Most LED strings used for holiday or festivity lighting work with the rectified current. The DC power produces a brighter light without any discernible flicker.
LEDs will never be seen here
edn.com/electronics-blogs/led-zone/4412955/LEDs-will-never-be-seen-here
That doesn’t mean they don’t exist. GE Commercial Lighting claims, in a recent press release, that there’s a dramatic transformation involving commercial lighting and design. LEDs, they claim, have found their way into places where they’ll never be seen by customers, including:
Inventory warehouses
Factories
Industrial spaces with tall, open ceilings
The primary reasons they’re finding their way into these spaces naturally include energy efficiency compared with previous HID systems and maintenance based on substantially slower change out. Not only is less labor involved, there is far less interruption to facility operations given the advanced machinery necessary to change bulbs on industrial floors.