Lumileds reduces number of bins for warm white LEDs

June 3, 2008
Using its Lumiramic phosphor technology, Lumileds is reducing the number of white LED bins for the benfit of the general lighting market.
Figure 1. Warm white bins eliminated Using its patented "Lumiramic" phosphor technology, Philips Lumileds has reduced the number of white color bins for its warm-white Luxeon Rebel LEDs (see figure 1).

The technology enables specific targeting for correlated color temperature (CCT), which enables Lumileds to control the color temperature and tint, and minimizes production variance.

The new technology will ultimately result in a single row of white bins along the black body locus (see figure 3). Each bin will be sized to represent a total space no more than 3 MacAdam ellipses.

Lumileds describes the binning of white LEDs is a “work-around” to manage the variation in white color and tint that are the result of today’s manufacturing processes. The inefficiencies of binning create structural vulnerability in the supply chain for the market.

Fig. 2. Fewer bins in cool and neutral To date, says Lumileds, there have been no solutions that decrease or eliminate this risk. The only way most manufacturers can consistently produce sufficiently large quantities of the desired bins for general lighting has been to increase the volume of white LEDs manufactured and discard those that don’t fit in the desired color spaces.

However, this does little to address the supply chain risk and produces tremendous waste, the cost of which must be absorbed by the market.

“For all the acknowledged benefits of power LEDs, such as efficiency, sustainability, and durability, we believe that providing a supportable, high color-quality supply of white LEDs is the single biggest challenge facing the power LED industry and today Philips Lumileds is addressing this head-on,” said Michael Holt, CEO of Philips Lumileds.

Figure 3. Single row of bins Over the last 18 months, flux improvements have resulted in power LEDs delivering upwards of 80 lm/W. Light output and efficiency has been a primary obstacle to adoption. Now that solid-state lighting systems can outperform fluorescent, the industry must continue to improve the quality, consistency and availability of white LEDs.

With a reduction in bin spaces for warm white already in place, Philips Lumileds will turn its attention to a similar reduction for neutral and cool white Luxeon Rebel products. When complete (as shown in figure 2), the process to remove additional bins and shrink remaining bins on the black body locus will commence.

The technology

Lumiramic phosphor technology utilizes a ceramic phosphor plate and Lumileds’ thin film flip chip (TFFC) technology. The process matches royal-blue (pump) TFFC die that have been characterized and sorted by wavelength to pre-measured ceramic phosphor (Lumiramic) plates.

By matching Lumiramic plates of the appropriate thickness with the correct wavelength of TFFC die in advance of final manufacturing, a specific CCT can be targeted.

While the concept is well understood, years of invention were required to identify phosphors and create the ceramic plates that would be stable in the intended environments. The TTFC die is also essential, since there is no anode or cathode in the light path.