Effect of refractive index of packaging materials on the light extraction efficiency of COB-LEDs with millilens array

Abstract

Lens arrays are introduced to diminish the total internal reflection (TIR) that happens at chip-encapsulant and encapsulant-air interfaces of chip-on-board light-emitting diodes (COB-LEDs), so as to improve the light extraction efficiency (LEE) of the COB-LEDs. However, the LEE of COB-LEDs with lens array depends on the refractive index of the encapsulant layer n e n c a p and lens array n l e n s , which was rarely concerned so far. Optical simulations based on a Monte Carlo ray tracing method, and experiments were conducted to investigate the effect of n e n c a p and n l e n s on the LEE of COB-LEDs with millilens array. The simulated results show that the TIR at chip-encapsulant, encapsulant-lens, and lens-air interfaces can be significantly diminished by regulating the n e n c a p and n l e n s , and the LEE of COB-LEDs decreases as the refractive difference of encapsulant layer and lens array | n l e n s − n e n c a p | increases. Compared to the COB-LEDs with only a flat encapsulant layer, the LEEs of blue and white COB-LEDs with n l e n s = n e n c a p = n I T O = 2 are enhanced by 246.2% and 50.6%, where n I T O is the refractive index of the top layer of the conventional LED chip. The experimental results agree well with the simulated results with normalized LEE deviation within 7.3%.

The Light Features and Bredigite Layout for Orthosilicate Phosphor in WLED Devices

“…From Figure 4, we can see the diffuse reflectance absorption spectra of CMS:Eu 2+ . It is possible to determine the Kubelka-Munk absorption coefficient (K/S) via a correlation: the absorbance (A) for CMS as well as CMS:Eu 2+ can be assessed with the reflectances (R) via an expression (Yu et al, 2021):…”

Utilizing the right phosphor in near-ultraviolet and blue light-emitting diode devices to generate white illumination

“…On the basis of the ηex alteration with wavelength under 35 A/cm 2 as well as ηex being the superior limit of energy performance, the energy performance in the near-UV LEDs would not receive any benefit under the wavelengths less than roughly 405 nm with the blue LEDs emission under the wavelength ranging from 440 to 450 nm, which is the common option for white illumination. Such InxGa1-xN LED activity indicates that the phosphors excitable under wavelengths less than 405 nm would barely have a practical use for white illumination with high need for performance [15], [16].…”

Combining ab initio and ab initio molecular dynamics simulations to predict the complex refractive indices of organic polymers

“…Organic polymers are now frequently used in various applications ranging from industrial developments to scientific research owing to their light weight, high machinability, excellent thermal performance, tunable colors and reasonable costs. Organic polymers have replaced inorganic optical glass and other materials in many fields and are expected to play a key role in the future, especially in the applications of optical system design, such as radiative cooling, 1,2 optical-thermal utilization of solar energy, 3 LED package design 4,5 and optical lens design. 6 However, most of the applications require a refractive index value larger than 1.7, while typical organic polymers only exhibit refractive index values in the range of 1.3–1.6.…”