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TECHNOLOGY / LED
Figure 4: The global lighting fixture market in 2017 (Source: Fredonia Group)
could make a significant impact on LED lighting over the next few years. One such company was Kangrong Fine Ceramic Co that demonstrated a new low cost ceramic material, K9-H, which stated 10x the heat dissipation of standard aluminum heat sinks. One reason the K9-H material offers superior performance is that the ceramic technology does not have regular particles at its surface which forms significant heat dissipation channels and extends the surface areas to improve heat exchange compared to metal surfaces which have similar particle sizes and shapes so the heat transfer only occurs at the outer most particle layers.
K9-H has a thermal conductivity of 25-39W/ m.k which is low compared to Aluminium at 203W/m.k however the thermal radiation rate of K9-H is 0.97 compared to Aluminium which only has 0.05. The overall LED heat dissipation for a heat sink design is a combination of the thermal conductivity and the thermal radiation rate so the LED junction temperatures of a system using K9-H is claimed to be 5 to 10% lower than the exactly equivalent heat sink made from aluminium.
There are significant advantages of K9-H including: • High insulation with volume resistivity is 1012~1013 over temperature ranges of 20~100°C.
• High safety • Non chemical corrosion, non-oxidizing, rust free.
• Environmentally friendly: no polluting chemicals.
• Abrasion resistance: compared with Aluminum, almost no abrasion.
• High surface area and heat dissipation
Kangrong demonstrated a family of ceramic based retrofit lamps and Heatsinks as shown in figure 5 for MR16’s and GU10’s.
LED Emitter updates
There has been considerable progress made by both Philips Lumileds and Cree recently announcing new products and improved colour quality through new production processes. Philips Lumileds has just announced the availability of the new Rebel ES which houses an increased LED die area within exactly the same package as the popular Rebel emitters. The new ES emitters offer significantly improved efficiency and light output performance offering 125lm/W efficacy at 350mA with a CCT between 3500-4500K. The efficacy reduces to 105lm/ W at 700mA however the emitter produces over 200 lumens (minimum) at this forward current.
In additional, the new Rebel ES emitters provide the same thermal management and packaging technology as the standard ANSI Rebel so that the performance does not degrade significantly with increased junction temperature.
Although pricing has not been announced the advantage of these new products is they can easily be used to replace standard Rebel products within current light fixtures and improve the performance without any redesign of the fixture layout. In addition, Philips Lumileds also announced they have started to yield results from their Lumiramic phosphor technology and the new LUXEON Rebel parts. The overall distribution of the manufactured LED product is significantly smaller than was previously possible or is possible with other solutions as shown in figure 6.
What is impressive with these results is the production yield is very tight in terms of white light distribution. Many LED Companies claim they have smaller LED Bins, but populating those bins usually comes at a cost, especially if the distribution of white light from production is wide. For example, a wide production distribution of colour temperatures leads to poor numbers of LEDs with smaller defined bins and therefore supply chain instability. Alternatively production volumes must be increased in order to provide sufficient LED numbers in the smaller bins. In the case of the new Rebel LED parts using Lumiramic phosphor, the actual population distribution is smaller and therefore smaller bins come naturally without cost. Recently, Cree announced they have improved their white light binning of multichip LED emitters with the industry’s smallest warm and neutral bins for their XLamp MP-L and MC-E EasyWhiteTM LEDs as shown in figure 7. The breakthrough provides a single two-step MacAdams ellipse bin per colour temperature, optimized to achieve incandescent-like colour consistency and eliminating the need to purchase multiple small bins and perform complex colour mixing.
EasyWhite binning is a unique feature of Cree multi-chip LED components that enables customers to specify a colour temperature and lumen output, simplifying LED system design and improving LED-to- LED colour consistency. Each bin, at the intersection of the black body locus and standard warm/neutral CCT points, is 94 percent smaller than the respective ANSI C78.377 quadrangle and 75 percent smaller than current Cree EasyWhite bins. XLamp MP-L and MC-E LEDs with EasyWhite
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