by John Cafferkey, Greentech Media
The rise of LED lightbulbs has been driven in large part by their environmental credentials, and rightly so. LEDs consume a fraction of the power used by traditional incandescent bulbs and have exceptional longevity, lasting up to 25,000 hours.
Most of an LED’s environmental impact (around 98 percent) is incurred during its use. Factors such as longevity and efficiency present the greatest opportunity for LED manufacturers to improve the environmental impact of their products. After that, the biggest influencing factor — the “greenness” of the power source itself — is out of manufacturers’ hands.
However, while only constituting around 2 percent of the overall environmental impact of an LED’s lifecycle, the manufacturing and recycling phases are becoming increasingly important considerations for LED manufacturers. The trend is being driven in part by corporate social responsibility and marketing, but there are also more pragmatic reasons to consider the whole lifecycle of LEDs — the most obvious is in cost savings through using recycled material.
One notable area where manufacturers can drive significant eco-improvements is in their selection of substrate, a choice that can allow for improvements at both ends of the product’s lifecycle.
The circular economy
Over the past few years, growing emphasis has been placed on the production of goods under the circular economy model. The aim of the circular economy is to develop products that have the smallest environmental impact possible, by keeping them in use for as long as possible and then recovering and reusing the materials at the end of life. This is in contrast to the more traditional “linear economy” model where a product is manufactured, used and disposed of, more often than not in landfill.
Over the next few years, billions of LED products are going to reach the end of their useful life. As this happens, the LED industry will need to adopt a multi-pronged approach to sustainability if it wants to maintain its image as an environmentally friendly technology.
This will involve sourcing materials that use minimal energy to produce and manufacture, and, ideally, use recycled materials where possible. To achieve this, manufacturers will need to design products with an eye on recyclability from the outset by sourcing materials that fit into the circular economy model and maintain their value at end of life.
LEDs and the need for thermally conductive substrates
High-power LEDs are much less efficient than usually assumed, which causes significant thermal challenges. While far more efficient than their incandescent predecessors, they only convert around 40 percent of the power input to light. This means some 60 percent of the power is converted into heat that needs to be removed to ensure the LED is kept within its safe operating temperature. As with any electronic device, overheating can have a detrimental impact on lifespan, light quality and color, and can ultimately lead to the LED failing.
LEDs come in a wide variety of packages, with high-power LEDs predominantly using a ceramic substrate. The substrate requires very specific properties — it must be thermally conductive, but electrically insulating. This generally limits the choice to relatively low thermal conductivity but low-priced alumina, or thermally effective but expensive aluminum nitride (AlN).
The high-power packaged LEDs are then mounted onto module printed circuit boards (PCBs), which, when combined with a heatsink and lens, become the luminaire (or bulb) that we know and love. Most general lighting luminaires will use a thermally efficient aluminum PCB (a metal-clad PCB or MCPCB) to enable the heat to reach the heatsink as efficiently as possible. When LEDs are placed close together on a PCB — in spotlights, for example — aluminum PCBs may not be effective enough and aluminum nitride PCBs tend to be used.
Eco-effects of manufacturing AlN vs. nanoceramic thermal substrates
AlN is a technically significant ceramic material. It has a composite thermal conductivity from 140 to more than 200 watts per meter-Kelvin and is naturally electrically isolating. It is, however, extremely difficult to manufacture. The most common approach to producing AlN for LEDs is carbothermal reduction and nitridation. Not only is this a power-intensive and expensive process, it also produces 160 grams of carbon dioxide as a byproduct for every 100 grams of AlN produced — and that’s excluding the amount of carbon used in extraction and production of the base material.
In short, manufacturing AlN is not very environmentally friendly.
AlN also generates a lot of waste when used as a PCB. It is brittle, and this leads to as much as a 20 percent fracture rate when it is being circuitized. These fractures only tend to get picked up at the end of the process once the material has undergone thin-film circuitization, leading to further waste of materials and energy costs.
Clearly, an alternative option that meets the thermal and electrical requirements of AlN would be ideal.
Cambridge Nanotherm has developed a unique nanoceramic PCB for just this purpose. The process converts the surface of a sheet of aluminum into a thin layer of ceramic. This ceramic layer acts as the dielectric, and, due to its thinness, acts as an extremely efficient thermal conductor, with a composite thermal conductivity of 152 watts per meter-Kelvin for a single-sided substrate. This makes it suitable for all but the most thermally demanding applications.
Not only is nanoceramic more cost-effective, easier to manufacture, and more robust than AlN, it is also far more eco-friendly to produce. While it requires high voltages during manufacturing (as part of the electrochemical oxidation process by which it is made), these voltages are only applied for a very brief period. It also produces no carbon dioxide waste, beyond that generated by the power source, and the chemicals used are sufficiently benign to be disposed of in regular sewers.
Recyclability of AlN vs. nanoceramic substrates
According to Recolight, the U.K.’s leading waste electrical and electronic equipment compliance scheme for the lighting industry, LEDs represent less than 1 percent of its lamp waste stream. Even the most efficient recycling scheme, in Norway, is only able to achieve around 3.5 percent. This is a sign of LEDs’ relatively recent introduction to the market and a testament to their longevity. However, in 10 years, LED recycling will be a significant challenge.
Whereas incandescent bulbs are recycled primarily for their glass (over 90 percent of their content), LEDs are more complex in their structure. Current recycling solutions involve crushing the bulb and then separating the various materials. Currently, LEDs are treated as “contamination” because they are so small and complex to recycle. This is starting to change as processes improve and the requirement to reuse the rare earth materials they contain becomes more pressing. By the time LED recycling becomes a significant issue it is likely that the technologies will exist to efficiently recycle die.
One of the most recyclable elements in LED bulbs is the aluminum that most MCPCBs and heatsinks are based on. Aluminum is one of the most easily and commonly recycled materials and can be recycled indefinitely without any deterioration in quality. Cambridge Nanotherm’s thermal management solution, being predominantly aluminum, can be recycled using existing infrastructure. What’s more, this process is ecologically sound, taking only around 5 percent of the energy used in the primary manufacture of aluminum from bauxite. Nanoceramic substrates based on aluminum are a perfect fit for the circular economy philosophy, offering manufacturers the ideal material to improve their carbon footprint while maintaining the same thermal properties and reducing costs.
In terms of a lighting product’s environmental impact, little is going to offer the kind of carbon savings that improvements in efficiency and lifespan can offer. That said, when you consider the billions of high-power LEDs on the market, small improvements really matter.
We’re about to enter the first phase where LEDs will reach the end of their life, and we will be inundated with bulbs that are not easily recyclable because they contain AlN. There is a grim irony when you consider the environmentally friendly LED bulb going to landfill while its inefficient predecessor is being recycled. However, through using the right materials, this can be minimized. Nanoceramics are not only the cost-effective alternative to AlN as a thermal management solution, they are also the environmentally friendly choice.
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