Effect of Chip Number on the Spatial Light Distribution of High-Power-Density LEDs

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript presents an experimental study on the spatial light distribution, correlated color temperature distribution, and thermal distribution characteristics of high-power density LEDs with varying chip quantities. The topic holds certain engineering application value, the selection of experimental subjects is clearly defined, and the overall structure of the manuscript is essentially complete. The authors compared the differences in optoelectronic performance, angular luminous intensity, spatial CCT, and thermal imaging among 4-, 9-, 16-, 25-, and 64-chip devices. The conclusions are largely consistent with the experimental results and provide certain reference value. However, there is still room for improvement in the manuscript regarding the explanation of certain definitions, the articulation of mechanisms, and the presentation of results. It is recommended that the authors make minor revisions based on the following comments.

1、Clarify the Criteria for Determining "Optical Saturation" or "Saturation Current":

The manuscript provides saturation currents for different devices (e.g., on page 5, the saturation current for the 4-chip device is 20 A, and for the 64-chip device is 160 A), but the basis for extracting these values is not clearly explained. It is recommended that the authors clarify whether the saturation point was determined based on a threshold decline in the light output growth rate, an inflection point on the curve (e.g., tangent method), or other quantitative criteria. This issue is directly relevant to several result analyses in the text (e.g., I-L characteristics, θ-L characteristics under saturation conditions). Adding this explanation would enhance the reproducibility and persuasiveness of the results.

2、Better Highlight the Boundary Conditions for Comparisons Between Different Devices:

This study focuses on comparing devices with different chip numbers, and the experimental approach is clear. However, it is recommended that the authors further elaborate on the differences in structural dimensions, emission areas, and packaging configurations among the devices (as shown in Table 1 on page 3). Additionally, they should emphasize that the conclusions are primarily based on the current sample set (using identical chips, the same packaging process, and a full parallel configuration). This would ensure a more rigorous expression of the comparative relationships and help readers more accurately understand the scope and prerequisites for how "changes in chip quantity" affect device performance.

3、Missing Key Parameters in the Experimental Methods Section:

In the experimental testing section on page 4, the authors describe the use of a rotating light-source measurement method and provide the angular sampling interval (10°) and the rotation stage accuracy (1°). However, they do not mention key parameters such as the integration time and number of samplings used by the spectrometer when collecting luminous intensity and color temperature data. It is recommended that this information be added to improve the reproducibility of the experiment.

4、Strengthen the Summary of Engineering Application Significance:

The manuscript has already derived several conclusions with application value, such as: increasing the number of chips helps improve the total light output, but does not imply a proportional increase in average performance per chip; the angular luminous intensity distribution remains close to a Lambertian distribution overall, while the spatial CCT is more sensitive to thermal coupling. It is recommended that the authors further highlight the specific implications of these results for the design optimization of high-power density LEDs at the end of the conclusion, to enhance the engineering guidance significance of the manuscript.

5、Minor Corrections Needed in Figures, Tables, and Text:

It is recommended that the authors consistently check the following issues in the revised manuscript:

(1) Inconsistent expression of some figure numbers in the main text.

(2) On page 11, the title of Table 2 does not fully correspond to its content; on page 16, the title of Table 3 repeats that of Table 2. Please verify and correct these.

(3) Minor spelling errors, extra spaces, and sentence coherence issues exist (e.g., "ceramic- packaged" on page 3 has an extra space).

6、Further Standardize the Use of Certain Technical Terms:

The term "thermal congestion" appears multiple times throughout the manuscript. It is recommended that a brief definition or explanation of this term be provided upon its first occurrence to help readers accurately understand its meaning. Alternatively, consider consistently using a more common term in the field, such as "thermal coupling effect," to maintain consistency and standardization of technical terminology.

Comments on the Quality of English Language

The English language would benefit from minor polishing to improve readability and overall clarity.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study systematically investigates the effects of chip quantities (4, 9, 16, 25, 64) on the light output capability, spatial light distribution, and spatial correlated color temperature distribution of high-power density LED devices, combined with infrared thermography to analyze chip temperature distribution characteristics. The research topic holds significant engineering application value. The experimental design is systematic, the data are substantial, and the conclusions provide a meaningful reference for the packaging design and chip integration of high-power density LEDs. The manuscript is well-structured, logically rigorous, and meets the journal's publication requirements. However, there are some areas for improvement concerning figure numbering, textual expression, and the depth of analysis. It is recommended that the manuscript be accepted after revisions.

1. Figure Numbering and Citation Errors:

 There are several instances where figure numbers in the text do not match the actual figures. Please carefully review and uniformly correct these. For example:

(1) On page 4, multiple occurrences of incorrect numbers like "Figure 4.2(a)" appear; these should be "Figure 2(a)".

(2) On page 11, the title of Table 2 is incorrectly written as "Variation in correlated color temperature (ACT) over the angular range…". It should instead refer to "ΔCCT". Furthermore, the content of Table 2 does not fully correspond to its title. Please correct this.

(3) On page 16, the title of Table 3 repeats the title of Table 2, while its content pertains to temperature differences. It is recommended to change it to "Average chip temperature difference (Avg. ΔT) relative to the 4-chip device".

2. Textual Expression and Grammatical Issues:

 Some sentences are redundant or lack grammatical precision. It is advisable to streamline or adjust them appropriately. For instance:

(1) Page 3: "In this way, ceramic- packaged white LED devices were fabricated, with a total device thickness of 800μm." It is suggested to change to: "Ceramic-packaged white LED devices were fabricated with a total thickness of 800 μm."

(2) Page 4: "The experimental setup adopts a rotating light- source measurement method." It is suggested to change to: "A rotating light-source measurement method was used in the experiment."

(3) Throughout the manuscript, the phrase "as shown in figure X" is repeated frequently and could be appropriately streamlined.

3. Enhancement of Data Analysis and Discussion:

On page 8, in the section on "θ-L characteristics under optical saturation conditions," the authors state that all devices exhibit a near-Lambertian distribution. However, no fitting results or deviation analysis compared to an ideal Lambertian distribution are provided. It is recommended to supplement this with fitting curves or quantitative deviation indicators to strengthen the persuasiveness of the conclusion.

4. Refinement of the Conclusion:

 The conclusion section is quite lengthy, and some parts overlap with the Results section. It is recommended to condense the conclusion appropriately, highlighting the innovative findings and engineering significance, and avoid reiterating experimental results point by point.

5. Optimization of Chart Presentation Details:

 Figures 3 to 6 contain numerous data points. It is recommended that the authors add notes in the figure captions regarding the measurement error range or repeatability test details to enhance the credibility of the data.

6. Terminology Standardization:

 Throughout the manuscript, terms describing "optical saturation" are mixed, such as "optical saturation," "light saturation," and "saturation condition." It is recommended to uniformly use "optical saturation" to maintain consistency in terminology.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript investigates the effect of chip number on the optical and thermal characteristics of high-power-density LED devices. LED samples with different chip numbers were fabricated and experimentally analyzed to study luminous intensity, spatial light distribution, correlated color temperature (CCT), and temperature distribution using thermal imaging.

Comments to Authors:

The manuscript would benefit from a clearer comparison with previously reported multi-chip LED studies to highlight what new insights are provided specifically regarding chip-number-dependent optical behavior.

In Section 3.1, the discussion of saturation current and luminous intensity could be strengthened by including quantitative metrics such as efficiency per chip or power density to better evaluate device performance.

The relationship between the infrared thermal imaging results and the observed CCT variations should be discussed more directly, particularly how the center-to-edge temperature gradient influences the angular CCT distribution.

Since thermal coupling plays a key role in the conclusions, additional details about chip spacing, heat dissipation conditions, or packaging geometry would help readers better interpret the thermal behavior of the devices.

Comments on the Quality of English Language

The manuscript is generally understandable; however, the English language could be improved to enhance clarity and readability.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This manuscript presents a systematic experimental study of how chip number affects the optical and thermal behavior of high-power-density LED devices. By comparing five devices with 4, 9, 16, 25, and 64 chips, the authors analyze luminous output, angular emission, correlated color temperature (CCT), and infrared thermal maps. The paper addresses a practically relevant device-engineering problem, and the central message is clear: increasing chip number enhances total output capability, but the gain is not proportional because of stronger thermal coupling. Overall, the study is interesting, well structured, and potentially suitable for publication after revision.

Main Strengths

• The work considers multiple complementary observables—light output, angular luminous-intensity distribution, CCT evolution, and thermal imaging—so the study has a coherent opto-thermal perspective rather than relying on a single metric.
• The comparison across five different chip-number configurations makes the observed trends more convincing than a simple two-sample comparison.
• A particularly useful result is that the normalized angular light distribution remains approximately Lambertian across all devices, while the CCT distribution and thermal behavior do depend more strongly on chip number and thermal congestion.

Suggestions for Improvement

The manuscript would be stronger if the experimental methodology and data treatment were described in greater depth. At present, the setup is described reasonably well, but it remains unclear whether the measurements were repeated on multiple devices of each type, whether the curves represent single measurements or averages, and what the uncertainty is for luminous intensity, CCT, beam angle, and temperature. Since several conclusions rely on differences between devices, the addition of error bars, repeatability data, or at least a concise uncertainty analysis would substantially improve the rigor of the work.

I also encourage the authors to discuss more explicitly that chip number is not the only varying parameter in the study. Because overall device size changes together with chip count, part of the observed behavior may also be influenced by package footprint, edge-to-center distance, and heat-spreading geometry. A short discussion clarifying this point would help the reader interpret the results more carefully.

The interpretation of the CCT behavior is physically reasonable and is one of the more interesting parts of the manuscript. However, some of the discussion currently sounds more definitive than the experimental evidence alone fully establishes. The authors may wish to distinguish more clearly between direct experimental observations and the proposed physical mechanisms, particularly regarding the combined roles of phosphor optical-path effects and center-to-edge thermal gradients.

Questions for the Authors About the Experiment

• How many devices were measured for each chip-count configuration, and were the reported results reproducible across samples?
• How exactly was “optical saturation” defined for each device?
• Were chip pitch and chip-to-chip spacing kept constant across all five array types?
• How was phosphor-layer thickness and phosphor loading uniformity controlled and verified for the different devices?
• For the infrared measurements, how was emissivity handled or calibrated, and do the reported temperatures correspond to surface temperature only, or are they intended as a proxy for junction temperature?

Minor Presentation Issues

• Table 3 appears to be mislabeled. Its caption refers to correlated color temperature variation, while the table contents correspond to average temperature differences. Is it referring to one of the figures above?
• There are several language and formatting issues that should be corrected in revision, including instances such as “Figure 4.2(a)” instead of “Figure 2(a)” and missing spacing in a few places.

Suggested References

The authors may also consider citing the following references to broaden the discussion and provide additional context:

• “Dispersion of organic exciton polaritons—A novel undergraduate experiment.” European Journal of Physics 43.3 (2022): 035301.
• “A hybrid organic–inorganic polariton LED.” Light: Science & Applications 8.1 (2019): 81.

Recommendation

In summary, this is a worthwhile and practically relevant experimental paper with clear trends and a useful opto-thermal perspective. I recommend publication after revision, with particular attention to experimental clarification, reproducibility and uncertainty, and several minor presentation corrections.

Author Response

Please see the attached file. Thanks! 

Author Response File: Author Response.pdf