White-light LED color design model allows rapid fine tuning
Their paper “Color design model of high color rendering index white-light LED module” published in Applied Optics details the fabrication of white-light LED modules using yttrium aluminium garnet (YAG) and nitride-based phosphors in blue and red LEDs built into 12x13mm arrays. Each module, a 5×5 LED array was made of 5 series of 4 blue and 1 red LED and fabricated with various proportions of phosphors and various densities of phosphors in silicone, with two types of red LEDs.
Moving away for the cheapest white LED solutions with a single blue chip and single yellow phosphor, or the one red and one blue chip combination with a single yellow phosphor, the 5×5 blue-red arrays with two phosphors exhibited a high color rendering index (CRI) and luminous efficacy, while the different proportions in phosphors could be tuned to achieve a precise correlated color temperature (CCT).
In their experiments, blue and red LED samples were prepared with and without phosphor packaging on a ceramic substrate (using 460–462nm blue LEDs and two types of red LEDs emitting 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.
For each variant, the spectra were measured and analysed so a color design model could be 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 they obtained was matching their experimental data in such a way that the maximum difference between the measured and color-design-model simulated CIE 1931 color coordinates was approximately 0.0063, around a correlated color temperature (CCT) of 2500 K.
This means the model now provides a rapid method to obtain the color fine-tuning of a white-light LED module, enabling the rapid modelling of a target spectrum.
This, the paper concludes allows manufacturers to fine-tune the color in a given production line, to maintain color consistency.
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