Collision on the road to solid-state lighting

New LED lamps have begun to appear on retail shelves, and many people are dazzled by the growth of the LED industry in the next few years. However, the road to success for LED lighting will not be smooth sailing, as there are some unexpected difficulties to overcome.

Trying to impose the latest technology on an infrastructure that has evolved over a century is no easy task. Some of these issues have been or will be solved, but there are still challenges, many of which will bring opportunities to competitors who already have the answers. Some of the potential issues to be faced now are price, color quality, thermal management, regulations, and user training. Because these issues are largely non-technical, design engineers do not need to understand them unless they are faced directly. These issues vary, depending on what new lighting bulb or custom LED lighting fixture the supplier is designing.

New LED bulbs

The US government has stipulated that the sale of incandescent lamps above 100W will be banned from 2012, and compact fluorescent lamps are expected to be the initial beneficiaries of this ban. But people want to know why consumers have not completely switched to compact fluorescent lamps simply because of the economic benefit that compact fluorescent lamps are more energy-efficient than incandescent lamps.

In fact, a large percentage of consumers have rejected compact fluorescent lamps for a variety of reasons, including flicker, color rendering, reliability vs. cost, slow startup, and environmental concerns about the mercury they contain. Although compact fluorescent lamps have addressed some of these issues, they are not desirable in the eyes of many consumers. In the short term, many of these consumers will switch to halogen incandescent lamps if their 100W incandescent lamps burn out.

This brings up the question: Can LEDs step into this void and become an available option for consumers? To date, there are no commercially available LED lamps to replace the ubiquitous 100W A19 incandescent lamp. The reason is that it is not physically possible to passively cool an LED with an output of 1500lm (the typical output of a 100W lighting tube) in an A19 form factor.

Since white LEDs are very efficient light sources, approximately one-third of the input power is converted into light, and the remaining two-thirds of the power is converted into heat in the LED. Therefore, at 100lm/W, approximately 100W of power must be consumed continuously and quickly. If this heat is not removed, the LED tube will quickly heat up to the maximum operating temperature of 120℃.

This problem may eventually be solved by improving the luminous efficacy of LEDs . Last year, the best cooled white LEDs achieved 100 lm/W of luminous efficacy; this year, several white LEDs have achieved luminous efficacy in the 120-130 lm/W range. This trend will not abate in the foreseeable future.

As LED conversion efficiency improves, thermal management improves at approximately the square of the efficiency, because the total power delivered to the LEDs decreases, and the percentage of heat generated by the input power decreases by a corresponding amount.

The rapid improvement in LED lighting efficiency is both a blessing and a curse. Customers who understand this, often early adopters, may wait for the technology to mature before purchasing a product, especially in the face of the current high prices of LEDs. Currently, a 75W PAR38 LED sells for around $40, which is a high price for most consumers, as they can buy a compact fluorescent lamp for less than $5 and an incandescent lamp for just pennies.

Yes, $40 is a reasonable price for a 10-15 year lifespan of LEDs. But consumers must learn to think of LEDs as capital improvements to their homes, rather than the usual consumer behavior of buying lamps. Will most consumers consider whether their home values ​​are flat or declining before making the switch? Probably not, but consumer interest in energy-saving technologies will continue to grow as we see a large number of marketing groups explaining the many advantages of LEDs.

Avoid immediate disposal

LED manufacturers also face the problem that their new lighting fixtures may be obsolete by the time they reach the store window. With the rapid improvement of SSL, time to market is critical. Although the actual design time can be shorter, obtaining the required certification from Underwriters Laboratories and then Energy Star can take several months.

Design engineers must be careful when selecting LEDs that may take several years to manufacture. Because LED products use the same package, it is easy for LED manufacturers to release higher lighting flux. As LED chip technology advances rapidly, LED packaging technology is also advancing rapidly and will play an equally important role in improving LED performance. LED manufacturers are very aware of this and have extended the life cycle of their products accordingly, and if possible, use new LEDs with the same PCB as previous models .

Color quality is perhaps the most difficult issue to solve. The industry has spent a lot of time and money on measuring and controlling the variability of white LED color. Chromaticity storage, such as OSRAM's ANSI, has become increasingly expensive for manufacturers. But color temperature and tight chromaticity storage are not the whole story, because light sources with the same chromaticity coordinates can have very different light wavelengths. If the spectrum is too different, different non-white surfaces will be produced under the two light sources.

Normally this is not a problem for LED lights with the same chromaticity coordinates, since their spectra are very similar, i.e. for an LED light replacing an incandescent lamp with the same color temperature (and therefore the same chromaticity coordinates), this is a potential problem, since the LED spectrum is very different from the incandescent lamp spectrum.

The Color Rendering Index (CRI) is a measure of how close the perceived color of a surface illuminated by a certain lighting source is to the perceived color of the same surface under an incandescent light source. A CRI of 100 indicates a perfect match. LEDs with a CRI of 80 or above are considered good, but more discriminating consumers may not think so.

OSRAM introduced their product Brilliant Mix by adding a red LED to a green-white LED (see Figure 1). When red light is mixed with green-white light, a white spectrum that more closely matches the spectrum of incandescent lamps is produced, especially at the end of the spectrum of red LEDs, where the chromaticity of conventional white LEDs usually decreases. The result is higher lighting efficiency and color refinement index.

Figure 1 By adding a red LED to the green-white LED, OSRAM's Brilliant Mix more closely matches the incandescent light spectrum.

LED lighting

In the short term, new LED lamps are a waste, but in the long term this is a huge opportunity for custom LED luminaires that can avoid the constraints of electrical lighting for 100 years.

LEDs offer huge advantages over the inefficiencies of incandescent and compact fluorescent lamps. LEDs can enable more complex form factors and more interesting and useful lighting patterns than traditional incandescent and compact fluorescent lamps. To capture these advantages, custom LED lighting fixtures are required. LEDs also offer additional features such as adjustable color temperature, enhanced brightness , and intelligent control.

Imagine a lighting fixture that can not only be dimmed, but also set to a desired color temperature. In other words, you might want to increase the intensity of light in a room, or add more color to the light. LEDs are the only light source with a spectrum that is sufficiently adjustable to make this possible. While this is technically possible, creating a user interface that makes these adjustments intuitive is challenging. Manufacturers who can design LED lamps that can adjust the color of light with simple controls will have a distinct competitive advantage.

Another possibility is to increase lighting levels, especially in office areas. The human eye begins to lose its ability to focus after the age of 40, and even those with excellent vision need glasses to help improve their vision in their 40s and 50s. Even so, many times these people may not need glasses to improve their vision outdoors because the human eye sees better under higher-intensity lighting conditions. When LED efficiency reaches the 150lm/W level, it will be possible to increase office lighting to 1000lx, rather than the typical 300lx in most offices under current conditions.

The opportunities for LED lighting become even greater when one starts to consider the constraints of conventional lighting. Typical home lighting requires circuits capable of handling approximately 20A per household. If all ceiling lighting fixtures were converted to LEDs, a 10A (or a few amps less) LED would be sufficient to light the entire house. And because LEDs are inherently low voltage devices, design engineers can implement lighting circuits with almost any voltage. Switching to a 12V or 24V DC system would eliminate the significant wiring costs associated with the large amount of standard wiring on the roof, especially with copper prices at their current high levels.

Low voltage circuits also reduce fire and electrocution hazards, and can improve the efficiency of photovoltaic /battery systems. Naturally, the switch to low voltage makes more sense for new buildings, but it is also feasible for retrofitting buildings that have abandoned the steeple. However, the lack of building standards can hinder progress, as electricians who still need a learning curve to do these installations.

Long-term problems

Other specific challenges facing LED luminaire designers are due to one of the most important advantages of LEDs – long life. First, the other components of an LED lighting fixture must have comparable lifespans, on the order of 50,000 to 70,000 hours. LED drivers , in particular, must be designed for high reliability and long life. In addition, thermal management is just as important for LEDs as it is for LED drivers. The choice of driver components is extremely important, and if you use an outsourced manufacturer, you want to make sure they don’t use lower quality substitutes – this is even more difficult when your outsourced manufacturer is overseas.

Worldwide distribution will help manage your supply chain, ensuring your products are made from the right components.

Although LED lamps have a lifespan of 10 to 15 years, customers still expect the lifespan of LED lighting to be infinite. When an LED lamp fails or is too dim after 15 years, customers do not necessarily have to buy or install a completely new lighting fixture because only the LED in the lighting fixture is damaged.

Customers will expect manufacturers to replace LEDs or LED modules.

When the LED in your luminaire fails, the LED you designed in the luminaire may have been outdated 10 years ago. Due to the lack of industry standards, your LED board or LED module will be a specific design, that is, no third party will provide a replacement module or board. If you cannot provide LED replacements, your customers will be very disappointed with you.

It will be interesting to see how the industry tackles these tough issues over the next few years. Often, new technologies present both technical and commercial challenges. Technical issues may seem the most difficult to overcome, but it is often business or regulatory issues that hinder progress and ultimately determine the technology's fate. One thing is certain - it will be a joyous journey!