May 8, 2017: Taiwanese researchers who have measured the spectrum of multi-die (blue and red LEDs) multi-phosphor white LED packages with changes in phosphors’ compositions and densities, have found a matching color design model, developed from Beer’s law and linear light conversion.
The study, presented in a paper “Color design model of high color rendering index white-light LED module”, talks about the fabrication of white-light LED modules which is done by using yttrium aluminium garnet (YAG) and nitride-based phosphors in blue and red LEDs built into 12x13mm arrays. Each module of 5×5 LED was made of five series of four blue and one red LED. It was fabricated with phosphors and densities of phosphors in silicone, with two types of red LEDs.
The 5×5 blue-red LEDs with two phosphors have a high color rendering index (CRI) and luminous efficacy, while the different proportions in phosphors was tuned to achieve a precise correlated color temperature (CCT).
Blue and red LEDs were prepared with phosphor packaging on a ceramic substrate by using 460–462nm blue LEDs and red LEDs that emitted at 614–616nm and 610–612nm. For the phosphor packages, silicone that contained phosphors was encapsulated in the cavity mold, and the LED chip was sealed.
While the spectra was measured for each variant, and analysed to see a color design model, which was established by measuring the optical absorption (using the blue LED spectrum and the optical emission of the phosphors) and Beer’s law and linear light conversion.
The model matched the experimental data in such a way that the maximum difference between the measured and color-design-model simulated CIE 1931 color coordinates was 0.0063, which means the model provides a rapid method to obtain the color fine-tuning of a white-light LED module.
This would allow manufacturers to fine-tune color, and maintain color consistency at the production line.