In this paper, we present our study in packaging efficiency for phosphor-converted white LED (pcW-LED). Then the limit of luminous efficacy of a pcW-LED in different types of packaging is estimated. In the calculation, the EQE of the blue die is assumed 81% and the Stokes loss is counted, we obtain the limit of luminous efficacy, which reaches 300 lm/W, when the color appearance is green-white and the corresponding CCT is between 4000K to 5000K. More consideration for practical limit take consideration of phosphor quantum loss and geometry loss, and the limit of luminous for CRI around 60 is around 240 lm/W, and for CRI larger than 80 is around 175 lm/W.

In this paper, we start from the study on the packaging efficiency of the phosphor-converted white LED via a new way to measure and calculate the blue light from the blue die to the encapsulation lens. Then we try to estimate the limit of luminous efficacy of a pcW-LED with Type VII structure. In the calculation, with the EQE of 81% of the blue die and Stokes loss, we obtain the optimal limit of luminous efficacy. The largest one reaches 300 lm/W, and occurs for green-white light with CCT from 4000K to 5000K. More practical limit is calculated in considering phosphor quantum loss and geometry loss, and the practical limit of luminous for CRI around 60 is around 210 lm/W, and for CRI larger than 80 is around 175 lm/W. Luminous efficacy will be sacrificed to obtain higher CRI. In order to know the real optical flux on the illuminated target, we introduce the optical utilization factor (OUF). Three application cases are discussed. The OUFs for light bulb, automotive head lamp, and street light are 90%, 60% and 45%, respectively. In considering human factors, it is interesting to find that a light source with lower luminous efficacy can perform higher illumination luminous efficacy (ILE). Therefore it is important to use ILE rather than LE when a light source is practically applied to lighting.

An essential factor of the particle number is exploited for the phosphor excitation in phosphor-converted white LEDs. The particle number can clearly reveal the dependence of the light output flux and the correlated color temperature upon the conventional parameters, thickness, and concentration of the phosphors in a simpler way. In addition, we also find that there might exist an optimal particle number for the maximal luminous light output. An empirical function is then proposed for successfully modeling the relation between the output light and the particle number.

In this paper, a precise simulation and detailed design of angular correlated color temperature (CCT) distribution of white LEDs covering a range of CCT from 2800K to 6500K is presented. In our best knowledge, it is the first time which the kind of research is presented. Besides, for a white LED with the CCT near 6500K, an optimum design of packaging structure with a silicone lens covering a phosphor dome performed an extreme small angular CCT deviation of 105K and 182K in simulation and the corresponding experiment respectively.

In this paper, to our best knowledge, it is the first time to present a precise simulation and detailed design of angular correlated color temperature (CCT) distribution of white LEDs covering a range of CCT from 2800K to 6500K. An optimized design of packaging structure with a silicone lens covering a phosphor dome performed an extreme small angular CCT deviation of 105K in the simulation and 182K in a corresponding real sample for a white LED with the CCT near 6500K.

As well known, the light emission characteristics of the high power light-emitting diodes (LEDs) are very sensitive to the various driving conditions, especially the injected electric current and the junction temperature in operation. In this work, the dependency of the emission light from high power LEDs upon the driving electric current and the junction temperature will be explored in details. One integrated measurement system is proposed for the study in simultaneously obtaining all the thermal–optic–electric characteristics of LEDs throughout the measuring. Based on the basic feedback control methodology, one simple maintaining procedure is applied for the stable light emission in high power LEDs. It shows the robustness of the maintaining procedure from the environment change with the least heat dissipation in the operation of the high power LEDs. The results imply that all the thermal, the optic, and the electric properties of the high power LEDs should be taken into consideration in the same time rather than separately when maintaining their operation.

Based on Monte Carlo ray tracing we present a study of GaN die with a reflective layer coated on a p-GaN surface inside the light guide as a planar light source. We simulated the lights extracted from the GaN die implanting pyramid microstructure on the top surface of sapphire or on the top surface of p-GaN. Micro pyramid array with different slanted angle from 5 degrees to 85 degrees is shown to effectively improve the light extraction efficiency. In addition, the pattern sapphire substrate with slanted angle of ten degrees is found to be an effective way to increase the lateral directionality than the surface texture.

In this letter, we present a new design for a light-emitting diode- based bike headlamp. The optical design contains two horizontal reflectors and a light pipe with two horizontal parallel mirrors. The designed illumination pattern in our simulations performs a contrast of 250 in the K-mark regulation, and it was measured to be 21 in the experiment with a not well-finished prototype, which was operated at 1 W. The contrast is higher than 5 as requested in the regulation.

In this paper, we present a study of light extraction of GaN-based LEDs through active/passive photon recycling, including sapphire-based and Thin-GaN based on Monte Carlo ray tracing. The mechanisms in enhancing light extraction incorporated with implanting micro pyramid (lens) array and lens encapsulation of both cavity photon recycling and quantum photon recycling are discussed. For an absorption coefficient of 200cm−1 in the active layer, both approaches perform more than 90% of light extraction efficiency through cavity photon recycling. For a heavy absorbed active layer, the quantum photon recycling could play an important role in light extraction.

In this paper, we demonstrate a method to calculate the phosphor particle numbers and study the relationship among phosphor particle numbers, light output and correlated color temperature (CCT) of LEDs under remote package type and dispensing package type. We also discuss the influence of the thickness and concentration of phosphors on the performance of LEDs. We compare the various thicknesses and concentrations to check the resultant CCT and the output flux, where we can see that the lumen output is almost equal as the phosphor particle numbers is similar with the CCT at 6500±200 and 5000±100 K under the remote package type.

In this paper, as to our best knowledge, we propose and demonstrate the first precise phosphor modeling scheme to simulate the chromatic performance of white LEDs with silicate phosphors. The phosphor model is useful to accurately simulate the power ratio of the blue and yellow lights emitted by the white LEDs and is important in white LED package.

High-performance, blue micro-size InGaN light emitting diodes (LEDs) with diameters of 3 to 20 μm have been fabricated. An ion implantation technique and a 12 micron electro-ridge were used to simplify fabrication processes. The 3 to 20μm LEDs that exhibited a large emission photon blue shift (87.5meV ~52.9meV) were observed in electro-luminescence (EL) spectra. Under an increased injection current, the quantum wells become populated with charge carriers, which screened the internal piezoelectric field and caused the energy blue shift of EL eventually. A high injection current caused a high junction temperature that narrowed the band gap (red shift). The size dependent energy shift is largely owing to the competition between the blue and the red shifts. At a bias voltage of 8.96V (which is 140% of the turn on voltage, 6.4V), the 10 μm device exhibited an injection current of 7.9mA. This value exceeds that in literature, i.e., 4mA at a bias voltage of 14V (which is 140% of the turn on voltage, 10V). This phenomenon may be owing to that the ion implantation and electro-ridge designs herein involved a lower series resistance. The external quantum efficiencies (E.Q.E.) of the micro size LEDs herein were all 0.4%~3.3%, which is better than the values reported in literature, which were ranged between 0.004% and 1.29% for an individual LED and an array LED, respectively. The E.Q.E. of the 15μm device at maximum injection current had the optimum value yet obtained for micro-size LEDs. The dependence of the blue shift and the E.Q.E. on the size warrants further study.