A surface may also exhibit both specular and diffuse reflection, as is the case, for example, of glossy paints as used in home painting, which give also a fraction of specular reflection, while matte paints give almost exclusively diffuse reflection.

This study measured near PFV, contrast sensitivity, and pupil size under different illumination levels to evaluate whether illumination could have an effect on these measures of visual function.

Ethical approval was granted for this study by the Institutional Ethics Committee for Human Research of Amity University Haryana (Ref No.- IEC -AIB/AUH/2021-22). A sample size of 34 was calculated (see Appendix). Fifty students from Amity University, Haryana, were screened for participation in this cross-sectional study. During the screening, they were provided with information about the study, and their consent was obtained. During the screening, participants underwent a measurement of visual acuity (Bailey-Lovie logMAR chart), and an ocular examination (slit lamp examination and dilated fundus examination) to exclude individuals with any ocular pathology, presbyopia, eye movement disorder, binocular vision anomaly, or systemic illness. Current contact lens wearers were not included (as this may have induced accommodation and convergence). Participants corrected visual acuity (BCVA) had to be of at least 0.1 for distance and N6 for near vision. They also had to have age-normative accommodation and vergence measurements. A total of 34 participants met the inclusion criteria and were included in the study.

Few materials do not cause diffuse reflection: among these are metals, which do not allow light to enter; gases, liquids, glass, and transparent plastics (which have a liquid-like amorphous microscopic structure); single crystals, such as some gems or a salt crystal; and some very special materials, such as the tissues which make the cornea and the lens of an eye. These materials can reflect diffusely, however, if their surface is microscopically rough, like in a frost glass (Figure 2), or, of course, if their homogeneous structure deteriorates, as in cataracts of the eye lens.

The visibility of objects, excluding light-emitting ones, is primarily caused by diffuse reflection of light: it is diffusely-scattered light that forms the image of the object in an observer's eye over a wide range of angles of the observer with respect to the object.

The study assessments included a cover test and a prism cover test (using a prism bar) to measure any deviation. Ocular motility was examined using the broad-H test, while the version was evaluated in nine specific eye positions. The push up test was utilised to determine the near point of accommodation monocularly (right and left) and with both eyes open. The measurement of the accommodative facility, expressed in cycles per minute, was conducted for both monocular and binocular viewing. Test targets of short, three-letter words in N8 font size were employed when assessing the lead and lag of accommodation, using the monocular estimated method. A typical lag was considered to fall between +0.25 and +0.75D (Scheiman & Wick 2014).

Background: Positive fusional vergence (PFV) is vital in maintaining fusion in critical and continuous near tasks such as reading or performing digital screen tasks. This study investigated how PFV changed under various lighting conditions.

What is illumination in the Bible

To prevent eye strain and fatigue, PFV was measured first. This was prioritised over the measurement of pupil diameter and contrast sensitivity because their measurements required less illumination and more convergence, potentially impacting the results. The study involved three different illumination conditions, with each subject being tested after a one-week interval. In the first week of testing, PFV, contrast sensitivity, and pupil diameter were measured under 50 lux lighting. Following a one-week break, the same procedures were repeated under 100 lux lighting. Finally, after one week of testing under 100 lux, the identical procedures were repeated, this time under 150 lux lighting conditions (see Figure 1). Contrast sensitivity threshold (Log CS) was measured using a Pelli Robson contrast sensitivity chart. A ruler was used to measure pupil diameter.

The vast majority of visible objects are seen primarily by diffuse reflection from their surface.[7][8] Exceptions include objects with polished (specularly reflecting) surfaces, and objects that themselves emit light. Rayleigh scattering is responsible for the blue color of the sky, and Mie scattering for the white color of the water droplets in clouds.

And, when a colored object has both diffuse and specular reflection, usually only the diffuse component is colored. A cherry reflects diffusely red light, absorbs all other colors and has a specular reflection which is essentially white (if the incident light is white light). This is quite general, because, except for metals, the reflectivity of most materials depends on their refractive index, which varies little with the wavelength (though it is this variation that causes the chromatic dispersion in a prism), so that all colors are reflected nearly with the same intensity.

Avci, AN and Memikoğlu, I. 2017. Effects of LED Lighting on Visual Comfort with Respect to the Reading Task. Available at https://www.researchgate.net/publication/320868090 [Last accessed 14 December 2021].

Jiang, BC, Gish, KW and Leibowitz, HW. 1991. Effect of luminance on the relation between accommodation and convergence. Optometry and Vision Science: Official Publication of the American Academy of Optometry, 68(3): 220–225. DOI: https://doi.org/10.1097/00006324-199103000-00010

The results of this study support that PFV measurements were affected by room illumination. Higher PFV values at near were measured in lower levels of illumination.

Types of illumination in slit lamp

According to recent studies, the quantity and quality of the illumination may significantly influence behaviour (Lança & Rowe 2019). Adequate fusional amplitudes are required for binocular vision stability. In the presence of vergence anomalies, a wide range of symptoms may be experienced, interfering with visual comfort and academic performance (Ansons & Davis 2013). As fusional vergence is necessary for maintaining fusion, clinicians typically investigate horizontal, and at times vertical, fusional vergence ranges for distance and near vision (Ansons & Davis 2013). These measurements are not typically recorded in different illumination levels (Lança & Rowe 2019). Positive fusional vergence (PFV) measurements can be determined by the responses reported by the patient, including the blur point, break point and recovery point (Ansons & Davis 2013).

Scheiman, M and Wick, B. 2014 Clinical management of binocular vision: Heterophoric, accommodative, and eye movement disorders. Lippincott Williams & Wilkins (LWW).

Kim measured contrast sensitivity using an Arden Contrast Sensitivity System in an incandescent electric lamp and the influence of illumination on the contrast sensitivity function. The illumination intensities were set to 50, 100, 200, 500, and 1,000 lux. The contrast sensitivity function was saturated at 500 lux light in both monocular and binocular conditions (Kim & Kim 1987). In our current study, we observed no statistically significant variation in contrast sensitivity across varying levels of illumination, specifically at 50, 100, and 150 lux. The findings of the study imply a link between illumination type and visual performance in clinical settings, and showcase that illumination levels can affect PFV measurements. The present research supports the clinical need to provide advice on appropriate illumination.

Ansons, AM and Davis, H. 2013. Diagnosis and management of ocular motility disorders. Wiley-Blackwell, 4th ed. DOI: https://doi.org/10.1002/9781118712368

Types of illumination PDF

Chen, Y, Wang, Y, Yu, X, Xu, A, Jiang, J and Chen, H. 2017. Effect of Illumination on ocular status modifications induced by short-term 3D TV viewing. Neural Plasticity, 2017(Special issue): 1432037, 1–9. DOI: https://doi.org/10.1155/2017/1432037

Ram, MS and Bhardwaj, R. 2018. Effect of different illumination sources on reading and visual performance. Journal of Ophthalmic and Vision Research, 13(1): 44–49. DOI: https://doi.org/10.4103/jovr.jovr_50_17

Diffuse reflectance spectroscopy can be used to determine the absorption spectra of powdered samples in cases where transmission spectroscopy is not feasible. This applies to UV-Vis-NIR spectroscopy or mid-infrared spectroscopy.[9][10]

Lança, CC and Rowe, FJ. 2019. Measurement of fusional vergence: A systematic review. Strabismus, 27(2): 88–113. DOI: https://doi.org/10.1080/09273972.2019.1583675

General illumination

Changes in near point of accommodation and near point of convergence have been noticed in different lighting conditions in terms of direct-indirect, direct, indirect, and compound (Wolska 2003). Jiang suggested that both vergence and accommodation tend to move toward new and individually characteristic resting postures when brightness is reduced for longer duration. An additional investigation determined that both the illumination mode and the utilisation of 3D viewing had an impact on ocular health (Jiang et al. 1991). This could be attributed to variations in luminance at the viewer’s position, the orientation of the light source, or the familiarity of the participants with their viewing surroundings (Chen et al. 2017). They suggested that front illumination is a favourable option for enhancing the visibility of 3D displays. Illumination source can also affect other ocular parameters, such as reading speed and visual performance. The reading rate was observed to be highest among males under compact fluorescent light, while females exhibited the fastest reading rate under fluorescent tube light (Ram & Bhardwaj 2018). The visual task setting parameters of white light and colour text were found to be more effective in average and low screen brightness conditions (Lin & Huang 2014). It was preferable to use blue as the font colour in low-luminance. This study examines the impact of varying levels of illuminance from LED lighting on users’ visual comfort and reading performance. Based on the guidelines provided by the Turkish Standards TS EN 12464, a lighting level of 1500 lux has been identified as optimal for reading tasks (Avci & Memikoğlu 2017).

Okada, Y, Kojima, T, Oohashi, T and Miyao, M. 2013. The effect of environmental illumination and screen brightness on accommodation and convergence. Digest of Technical Papers—SID International Symposium, 44(1): 1078–1081. DOI: https://doi.org/10.1002/j.2168-0159.2013.tb06411.x

Diffuse reflection from solids is generally not due to surface roughness. A flat surface is indeed required to give specular reflection, but it does not prevent diffuse reflection. A piece of highly polished white marble remains white; no amount of polishing will turn it into a mirror. Polishing produces some specular reflection, but the remaining light continues to be diffusely reflected.

Microsoft Excel 365 and SPSS (version 27.0.0) were used for descriptive and inferential date statistics respectively. The normality of the data was assessed using the Shapiro-Wilk test, revealing that the data was not normally distributed. Friedman’s test was employed to compare the near PFV across all three illuminations. Similarly, Friedman’s test was used to compare PFV, contrast sensitivity, and pupil diameter across the three illumination environments. The Wilcoxon signed rank test was used to check the comparison of near PFV between two different levels of illumination (50 and 100, 100 and 150, 50 and 150 lux).

Illumination lighting meaning

The study was conducted in accordance with established ergonomic guidelines, ensuring adherence to proper ergonomic standards. The ceiling was equipped with three 15-watt fluorescent bulbs, each of which could be controlled independently. This experiment examined three commonly employed illumination modes, and their brightness was measured using a lux meter. Mode A involved a viewer’s position illumination of 50 lux, achieved with a single fluorescent lamp. Mode B provided illumination of 100 lux at the viewer’s position, utilising two fluorescent lamps. Mode C employed three fluorescent lamps, illuminating 150 lux at the viewer’s position.

Wolska, A. 2003. Visual strain and lighting preferences of VDT users under different lighting systems. International Journal of Occupational Safety and Ergonomics, 9(4): 431–440. DOI: https://doi.org/10.1080/10803548.2003.11076580

This mechanism is very general, because almost all common materials are made of "small things" held together. Mineral materials are generally polycrystalline: one can describe them as made of a 3D mosaic of small, irregularly shaped defective crystals. Organic materials are usually composed of fibers or cells, with their membranes and their complex internal structure. And each interface, inhomogeneity or imperfection can deviate, reflect or scatter light, reproducing the above mechanism.

Abramson, CI, Page, MC, Zolna, M, Howard, W, Aquino, IS and Nain, S. 2007. A preliminary study of illumination levels in university and elementary classrooms in Campina Grande, Brazil. Journal of Social Sciences, 3(3): 155–158. DOI: https://doi.org/10.3844/jssp.2007.155.158

Illumination of light formula

Near point of convergence was measured using an accommodative target. The measurement of fusional vergence amplitude (prism dioptres), both for distance and near vision, was conducted using a prism bar with step vergence. The evaluation included both negative fusional vergence and PFV. The normative values and diagnostic standards set by Scheiman and Wick were used as a reference (Scheiman & Wick 2014).

Results: Pupil diameter changed significantly in different room illuminations (p = 0.00). There was no significant difference in contrast sensitivity across the three levels of room illumination (p = 0.368). Mean PFV (SD) (blur) was 14.5 (2.5) in 50 lux, 10.2 (2.2) in 100 lux, and 8.2 (2.1) in 150 lux. Under 50, 100 and 150 lux, respectively, the mean PFV (SD) (break) values were 16.7 (2.4), 13.4 (1.8), and 10.8 (2.2), and the mean PFV (SD) (recovery) values were 13.3 (2.1), 10.7 (2.1), and 7.5 (2.7). With increased illumination levels, PFV blur, break, and recovery values were significantly lower (p < 0.001).

Light illumination level

This study was approved by the Institutional Ethics Committee for Human Research of Amity University Haryana (AUH)- Ref No.- IEC-AIB/AUH/2021-22.

Diffuse interreflection is a process whereby light reflected from an object strikes other objects in the surrounding area, illuminating them. Diffuse interreflection specifically describes light reflected from objects which are not shiny or specular. In real life terms what this means is that light is reflected off non-shiny surfaces such as the ground, walls, or fabric, to reach areas not directly in view of a light source. If the diffuse surface is colored, the reflected light is also colored, resulting in similar coloration of surrounding objects.

Diffuse reflection is the reflection of light or other waves or particles from a surface such that a ray incident on the surface is scattered at many angles rather than at just one angle as in the case of specular reflection. An ideal diffuse reflecting surface is said to exhibit Lambertian reflection, meaning that there is equal luminance when viewed from all directions lying in the half-space adjacent to the surface.

I would like to express my special thanks to my mentors Mr. Sourav Karmakar, Dr. Gaurav Kumar Bhardwaj, Animesh Mondal, and Dr Vidyut Rajhans for the time and effort they provided throughout the year. Your useful advice and suggestions were helpful to me during the project’s completion. In this aspect, I am eternally grateful to you.

Diffusion affects the color of objects in a substantial manner because it determines the average path of light in the material, and hence to which extent the various wavelengths are absorbed.[6] Red ink looks black when it stays in its bottle. Its vivid color is only perceived when it is placed on a scattering material (e.g. paper). This is so because light's path through the paper fibers (and through the ink) is only a fraction of millimeter long. However, light from the bottle has crossed several centimeters of ink and has been heavily absorbed, even in its red wavelengths.

Our findings are similar to the results of others, where increased PFV was measured as room illumination decreased (Jiang et al. 1991). PFV has also been found to change in different illumination while using a visual display unit (Majumder & Sinathamby 2017). When measuring accommodative and convergence demand during observation of a 3D object under two different lighting conditions, accommodative and convergence demands have also been found to be higher under low-light conditions compared to bright-light conditions (Okada et al. 2013).

Methods: This cross-sectional study recruited 34 participants aged between 21 and 25 years, with best corrected visual acuity (BCVA) 0.0 logMAR and insignificant refractive error. Three different illuminations—low illumination (50 lux), medium lighting (100 lux), and high illumination (150 lux)—were used to examine the ocular parameters PFV (blur, break, and recovery points), contrast sensitivity and pupil diameter.

Illumination, a crucial workplace component, impacts employees’ productivity and working conditions. Appropriate illumination degree and distribution are required for employees to operate at their best. “Varying levels of illumination may impact the ocular function”, “Advice on the optimum standards for reading illumination has been suggested by various organisations”, and “The Indian National Electric Code of 2011 recommended that illumination for reading should be 300–700 lux, and the Central Building Research Institute of India advises 200–500 lux for tasks like reading” (Ram & Bhardwaj 2018). These recommendations are based on the Indian Standard Code of Practice for Industrial Illumination (Ram & Bhardwaj 2018).

Illumination lighting design

Conclusions: PFV values were significantly higher in lower illumination. Clinicians should be aware that room illumination affected the PFV values measured.

The present study revealed a significant increase in near-positive fusional vergence (PFV) measurements under lower illumination levels, specifically in blur, break, and recovery points. As anticipated, the size of the pupils exhibited a notable increase under conditions of reduced illumination. There was no observed alteration in contrast sensitivity across varying levels of illumination.

Majumder, C and Sinathamby, L. 2017. Effect of illumination over positive fusional vergence when using VDU as target. Journal of Clinical & Experimental Ophthalmology, 8(3): 1–5. DOI: https://doi.org/10.4172/2155-9570.1000656

Thirty-four participants who met the inclusion criteria, completed the study over three weeks. The mean age group of participants was 23.08 ± 1.40 years. This study included 15 males (46%) and 19 females (56%).

A surface built from a non-absorbing powder such as plaster, or from fibers such as paper, or from a polycrystalline material such as white marble, reflects light diffusely with great efficiency. Many common materials exhibit a mixture of specular and diffuse reflection.

Visual problems, attention issues, nutritional deficiencies, and general declines in health and mood have all been linked to inadequate illumination. It has been shown that the proper illumination can help counteract these effects, boost academic performance, and solve challenges. Brightness can significantly impact behaviour, as well as school and workplace performance (Abramson et al. 2007). Increased light brightness has been demonstrated to reduce stressful workload and boost productivity (Abramson et al. 2007).

In 3D computer graphics, diffuse interreflection is an important component of global illumination. There are a number of ways to model diffuse interreflection when rendering a scene. Radiosity and photon mapping are two commonly used methods.

Lin, CC and Huang, KC. 2014. Effects of lighting color, illumination intensity, and text color on visual performance. International Journal of Applied Science and Engineering, 12(3): 193–202.

The most general mechanism by which a surface gives diffuse reflection does not involve exactly the surface: most of the light is contributed by scattering centers beneath the surface,[2][3] as illustrated in Figure 1. If one were to imagine that the figure represents snow, and that the polygons are its (transparent) ice crystallites, an impinging ray is partially reflected (a few percent) by the first particle, enters in it, is again reflected by the interface with the second particle, enters in it, impinges on the third, and so on, generating a series of "primary" scattered rays in random directions, which, in turn, through the same mechanism, generate a large number of "secondary" scattered rays, which generate "tertiary" rays, and so forth.[4] All these rays walk through the snow crystallites, which do not absorb light, until they arrive at the surface and exit in random directions.[5] The result is that the light that was sent out is returned in all directions, so that snow is white despite being made of transparent material (ice crystals).

A previous study of accommodation and convergence levels using a 3D object in two different illumination levels revealed that accommodation led the convergence in brighter lighting. In contrast, accommodation and convergence were identical in average illumination (Jiang et al. 1991). In low illumination, convergence led the accommodation (Wolska 2003). Convergence and accommodation efforts have been shown to increase in low illumination levels, whereas in a brighter environment, the subject needs less accommodation and convergence (Okada et al. 2013).

The measurements of PFV at near in the different levels of illumination are shown in Figure 2 (blur point), Figure 3 (break point), and Figure 4 (recovery point). As illumination increased, the PFV measurement decreased for the blur, break, and recovery points. There was a statistically significant effect of illumination on near PFV: blur (p < 0.001), break (p < 0.001), and recovery (p < 0.001) points (Friedman test) (Table 1). The difference in the PFV at near, between each level of illumination, was significant for the blur, break, and recovery points (Wilcoxon signed rank test) (Table 2).

We recognise the limitations of the study as we had a limited sample size (although this was calculated), and a limited number of illumination levels. We also recruited young adults who were asymptomatic and had good vision, which limited our ability to make conclusions about clinical populations or clinical scenarios. Future studies may include recruiting participants in different age groups, analysis of other vergence and accommodation parameters, and recruitment of clinical populations.

Kim, CS and Kim, HK. 1987. Effect of Illumination on contrast sensitivity. Journal of the Korean Ophthalmological Society, 28(4): 729–732.

For simplicity, "reflections" are spoken of here, but more generally the interface between the small particles that constitute many materials is irregular on a scale comparable with light wavelength, so diffuse light is generated at each interface, rather than a single reflected ray, but the story can be told the same way.

Both monocular and binocular comparisons of contrast sensitivity with different illumination were studied. The mean (±SD) contrast sensitivity in 50 lux (right eye 1.80 ± 0.15, left eye 1.80 ± 0.15, both eyes 1.95 ± 0.15), 100 lux (right eye 1.80 ± 0.15, left eye 1.85 ± 0.15, both eyes 1.95 ± 0.15), 150 lux (right eye 1.95 ± 0.15, left eye 1.95 ± 0.15, both eyes 1.95 ± 0.15). There was no statistically significant difference between contrast sensitivity at different illumination levels (RE: p = 0.36, LE: p = 0.36, or BEO: p = 0.36). Pupil diameter measurements are shown in Table 3. As expected, as illumination increased, pupil diameter significantly decreased (Friedman test).

Most materials can give some specular reflection, provided that their surface can be polished to eliminate irregularities comparable with the light wavelength (a fraction of a micrometer). Depending on the material and surface roughness, reflection may be mostly specular, mostly diffuse, or anywhere in between. A few materials, like liquids and glasses, lack the internal subdivisions which produce the subsurface scattering mechanism described above, and so give only specular reflection. Among common materials, only polished metals can reflect light specularly with high efficiency, as in aluminum or silver usually used in mirrors. All other common materials, even when perfectly polished, usually give not more than a few percent specular reflection, except in particular cases, such as grazing angle reflection by a lake, or the total reflection of a glass prism, or when structured in certain complex configurations such as the silvery skin of many fish species or the reflective surface of a dielectric mirror. Diffuse reflection can be highly efficient, as in white materials, due to the summing up of the many subsurface reflections.

Up to this point white objects have been discussed, which do not absorb light. But the above scheme continues to be valid in the case that the material is absorbent. In this case, diffused rays will lose some wavelengths during their walk in the material, and will emerge colored.