Guoxing He

By using spectral loss simulation, it was found that six spectral bands are needed to produce a daylight simulator with good performance. The optimization model for both Commission Internationale de l'Eclairage metamerism index and luminous efficacy (LE) of light‐emitting diode (LED) daylight simulator (LDS) was developed. The optimal LDSs with AA grade for D50, D55, D65, and D75 illuminants should consist of the violet LEDs with violet phosphor excited by an ultraviolet chip, and the white LEDs with green, yellow, and red phosphors excited by a blue chip. Their limit luminous efficacies under the ideal case could reach 179 to 204 lm/W. And finally, a scheme for a spectrally tunable LDS with AA grade was presented.

An optimization model for luminous efficacy of a spectrally tunable light‐emitting diode (LED) daylight simulator under constraint of metamerism index was developed. It was first reported that the optimal spectrally tunable LED daylight simulator of AA grade for D50, D55, D65, and D75 standard illuminants could consist of two quantum dot‐integrated LEDs (QDLEDs) with the ultraviolet chip and two other QDLEDs with the blue chip. The optimized spectral parameters of each QDLED, as well as photometric and colorimetric performances of D50, D55, D65, and D75 daylight simulators, were obtained by maximizing luminous efficacy under the metamerism index for both a visible and ultraviolet range less than 0.25. The limit luminous efficacies of four daylight simulators using four QDLEDs under the ideal case will reach 181 lm/W to 205 lm/luminous efficacies with a radiant efficiency of both the ultraviolet and blue chips of 60%, as well as a quantum efficiency of a quantum dots layer of 90%, will reach 100 lm/W to 112 lm/W.

The optimal spectral parameters and photometric performances of white LEDs with red LEDs instead of phosphor (pc/R-WLEDs) for the color fidelity index (R_f) above 97 at correlated color temperatures (CCTs) of 2700 K to 6500 K have been obtained based on the luminous efficacy (LE) model. We have first reported four real pc/R-WLEDs with R_fs of 96–97 and LEs of 120–124 lm/W at CCTs of 2969 K, 4468 K, 5682 K, and 6558 K by using blue (448 nm) and red (650 nm) LEDs, as well as green (507 nm) and yellow (586 nm) phosphors. As compared with phosphor-converted white LEDs (pc-WLEDs) as well as quantum dots white LEDs (QD-WLED), it was found that the pc/R-WLEDs, not the QD-WLED as widely expected, make strong candidates for excellent color rendition, especially in the low color temperature range, for replacing current pc-WLEDs in the future.

This is a comment on “Optimization of a spectrally tunable LED daylight simulator” (Color Res Appl. 2017;42:419‐423). We found that full widths at half maximums (FWHMs) of light‐emitting diodes (LEDs) used in the six channels for daylight simulators given by Wei were 50 nm, not 30 nm. Therefore, it is impossible to implement AA‐grade daylight simulators with six LED channels. By our simulation, it was found that at least seven LEDs channels with FWHMs of 30 nm are required to produce a spectrally tunable daylight simulator with AA‐grade by appropriate intensity combinations. Furthermore, the spectrally tunable AA‐grade daylight simulators using six, five, and four channels were simulated. We have first reported that the scheme for the spectrally tunable daylight simulator with AA‐grade using three, four, and five types of phosphors or quantum dots excited by an ultraviolet LED.

This paper aims to provide an effective measurement method for the distribution of deformations and strains focusing on the response to external loading of bone-implant interfaces. To achieve this target, a novel speckle interference imaging method is proposed by introducing phosphate buffer saline medium, in which the samples were completely placed into a phosphate buffer saline solution medium to stable the water molecules. The stability of interferometry imaging is analyzed by using the concepts of co-occurrence matrix and moment of inertia. A series of experiments to measure load-driven deformation and strain in the bone-implant interface was carried out, and the experiments results were analyzed and discussed. It shows that the proposed method is feasible and effective for the no-contact strain measurements of biomaterials in a physiological condition. The proposed strain distribution sensing system will contribute to evaluating computational simulations and improving selection of implant designs and materials.

The spectral optimization for maximizing limited luminous efficacy (LLE) of correlated color temperature (CCT) tunable white light-emitting diodes (LEDs) with two, three and four color perovskite quantum dots (QDs) excited by a blue chip was investigated under the constraint of designated ultrahigh color rendering index (CRI) and color quality scale (CQS). The results show that high quality white lights with CRIs of 96-97, CQSs of 95-96, and LLEs of 243-225 lm/W at CCTs of 2700 K to 6500 K could be realized by the QDs-converted white LEDs (QD-WLEDs) using a blue chip and different combinations of perovskite quantum dots. The luminous efficacies of QD-WLEDs are expected to reach 114 to 122 lm/W at CCTs of 2700 K to 6500 K, if the radiant efficiency of a blue chip is 60% and the real PLQY values of perovskite QDs are 75%. These results demonstrate that perovskite QD-based LEDs are expected to be promising in next generation display and lighting technologies.