A Study on Pendant and Blackboard Asymmetric Lens LED Luminaires for Optimal Illumination in Classrooms

Comment 1.1: There is no information on outside light. If the photometric calculations are made without outside light, this should be mentioned.

Response 1.1: Thank you for your observation. We have clarified that comparisons were made between computed illuminances without daylight and measured illuminances using curtains to minimize outside light (less than 4 lux). Lines 256-257.

Comment 1.2: L 89-91. The objective was to utilize the uniformly painted white ceiling as a large, secondary light source, effectively eliminating the common problems of glare and shadow.

This statement is bold since it does not consider what can happen when exterior light is combined with interior light, especially during the solar midday.

Response 1.2: We appreciate your feedback. We have revised the statement to specify that curtains are used to minimize direct solar beams, ensuring the intended lighting effects are maintained. Lines 112-115.

Comment 1.3: In L 205. Table 1, L 230 Table 2, L 284-286 and in other paragraphs of the article lx, cd/m², lm, are used to show the magnitudes of the illumination obtained. All these parameters give photometric values from the photopic sensitivity curve.

If the objective of this work is to try to reflect natural light as best as possible, the Equivalents would have to be calculated daylight Illuminance (EDI).

Response 1.3: Thank you for your insightful suggestion. The primary focus of this work is on enhancing the quality of light distribution in learning environments by achieving uniform, soft, and diffused lighting that minimizes shadows and improves luminous uniformity, rather than specifically targeting Equivalent Daylight Illuminance (EDI). Therefore, the photometric values used were chosen to reflect these goals.

Comment 1.4: In line 86 and in paragraphs L 267-269 and L 276-278 it is stated that with the lighting method proposed in this project and the white ceiling, the following is obtained: appearance of natural skylight

The illumination will have the appearance of the luminaire's spectral distribution. It cannot be stated that the illumination will have the appearance of natural skylight natural without knowing and displaying the spectral distribution of the luminaire.

Response 1.4: Thank you for your valuable feedback. We have clarified in line 307-309 that 'the appearance of natural skylight' in our study refers to qualities such as omni-directional, shadow-free distribution and broad light coverage, rather than replicating the exact spectral characteristics of natural daylight. Additionally, we have removed line 86, the reference to Human-Centric Lighting (HCL) recommendations, as it does not directly contribute to our methodology.

Comment 1.5: L 405-407. Both PAL and BAL luminaires significantly elevate classroom lighting by replicating the soft, even illumination of natural skylight. This improved lighting quality enhances students' focus, reduces visual fatigue, and improves the overall aesthetic of the learning space.

This statement of the conclusions cannot be demonstrated with any type of lighting with photometric magnitudes that have not considered the incidence through the cornea of the interior and exterior light together, in addition to lighting that varies in its intensity and spectral distribution throughout the day.

Response 1.5. Thank you for your feedback. We have revised the statement in lines 405-407 to remove the comparison with natural skylight and instead highlight the benefits of our solution within modern artificial lighting environments (lines 436-438).

Comment 2.1: In the (Abstract), what do you mean with: (935 ÷ 1000 lx) and (660 ÷ 720 lx)?

Response 2.1: Thank you for pointing this out. We have revised the sentence in the abstract to clarify the illuminance values, specifying that ceiling illuminance ranges from 935 to 1000 lx and workspace illuminance from 660 to 720 lx, with reduced glare (UGR < 10). This adjustment enhances readability and precision in reporting our findings. (Lines 21-24).

Comment 2.2: Please add a paragraph for paper organization (at the end of your "Introduction")

Response 2.2: Thank you for your suggestion. We have added a paragraph at the end of the Introduction to outline the organization of the paper, providing a roadmap for readers to follow the structure and content in each section. (Lines 91-96). Additionally, we have updated the references to include recent literature relevant to our research direction (lines 33-41).

Comment 2.3: Please add a block diagram (or a flowchart) to describe your steps.... This will be easier for the reader to follow the procedure.

Response 2.3: Thank you for the suggestion. We have added a flowchart (Figure 1) at the beginning of Section 2, along with a brief explanation in the main text (lines 98-105), to provide a clearer overview of the design and optimization steps.

Comment 2.4: The dimensions you considered for the classroom need a reference. Is this the standard?

Response 2.4. Thank you for your comment. The classroom dimensions used in our study are not based on an official standard but represent a typical classroom size commonly found in our country. This choice reflects the practical conditions under which the luminaires are likely to be applied.

Comment 2.5: Some equations need reference(s). Ex: Eq. (1).

Response 2.5: Thank you for your observation. These equations, including Eq. (1), were developed by us based on commonly used mathematical functions, such as the logistic function, to fit the specific requirements of our study. We have not cited external references, as these equations are custom applications of standard mathematical forms.

Comment 2.6: The peaks in Fig. 2 must be explained. Why both exist at 80 degree and where is the position in the classroom.

 Response to 2.6: Thank you for your comment. We have added an explanation in lines 170-174 to clarify the significance of the peaks at ±70 degrees, which indicates the primary angles of light distribution for each luminaire. These angles ensure balanced illumination across the room. The initial positions of the luminaires (P1, P2, and P3) are shown in Figure 2, and these may be adjusted during the lighting simulation phase to optimize uniformity in different lighting scenes.

Comment 2.7: The obtained results are very good. I see a table of comparison for different scenarios. But I do not see any comparison with previously published results.

Response to 2.7: Thank you for your positive feedback on the results. The purpose of this study is to validate our design and optimization procedure. To our knowledge, no directly comparable results have been published, or existing results vary significantly in methodology and context, making direct comparisons challenging.

Commend 2.8. The (Conclusion) section needs some numerical values of the main findings.

Response to 2.8: Thank you for the suggestion. We have added numerical values in the Conclusion section to summarize the main findings, including average illuminance levels on the ceiling and working surfaces, uniformity values, Unified Glare Rating (UGR), and power density. These additions provide a clearer quantification of the improvements achieved with the PAL and BAL luminaires. (Lines 436-438)

Comment 3.1: This paper relates to a solution for optimal illumination of a classroom with recently developed LED technologies (Pendant Asymmetric Lens and Blackboard Asymmetric LEDS luminaires in a tropical country that requires fan cooling mounted at the ceiling. This would normally create rotating shadows.  The authors propose some configurations that improve illumination to reduce glare, and these rotating shadows. The solution approaches sky-light illumination.

The paper is well presented and well written with ray tracing simulations to support the work.

I have only one suggestion to improve the paper: The traditional blackboard to be used with chalks, in my opinion, has almost been superseded by the whiteboard with markers. Please write a paragraph of how the use of the whiteboard could impact on your analysis as the whiteboard would increase reflectivity from the wall it is placed and if it would produce some residual glare.

Best Regards

Response to Comment 3.1: Thank you for your positive feedback and thoughtful suggestion. We agree that the transition from traditional blackboards to whiteboards could impact classroom lighting conditions, especially due to the increased reflectivity of the whiteboard surface. In our study, we considered the blackboard's reflectance at approximately 9%, resulting in a luminance of around 27 cd/m², which is below the recommended 72 cd/m² for optimal active learning, as noted by de Vries. To address this, we propose transitioning to matte whiteboards with black markers to increase vertical luminance, enhancing both visual perception and student alertness.

However, as you mentioned, the currently available whiteboards are often glossy, which may produce some residual glare. We have not yet conducted experiments to compare the impact of matte blackboards versus matte whiteboards on visual acuity. We appreciate this suggestion and will consider it as part of our future research to further investigate and refine the optimal classroom lighting setup.

Best regards.