The survey results from 112 studio users were first examined in terms of respondent characteristics to support the validity of the findings (Table 3). The age distribution showed that 7% were under 20, 76% were from 20-30, 13% were from 31-40, and 4% were above 40, consistent with typical National Diploma (ND) and Higher National Diploma (HND) student profiles. Gender analysis indicated that 93.8% of respondents were male and 6.2% female, reflecting the persistently low female enrolment in technical programs in Northern Nigeria. All respondents (100%) had either studied or were currently studying at the Polytechnic, with 67% being graduates and 33% current students, and all (100%) reported using the Architectural Design Studio, confirming their suitability to evaluate lighting conditions.

In terms of studio use, 54.5% of respondents spent more than 5 h per day in the studio, 30.4% spent 4–5 h, and 15.2% spent 2–3 h, indicating substantial exposure to the space and its visual environment. Reported activities included drawing/drafting (92.9%), reading (36.6%), discussions (32.1%), lectures (48.2%), and modelling/jury sessions (1%–2%), underscoring the range of visually demanding tasks undertaken in the studios.

A post-occupancy survey of 112 architectural design studio users evaluated nine visual performance variables on a five-point Likert scale (1 = Strongly Disagree to 5 = Strongly Agree), with mean scores classified as <1.25 (Strongly Disagree), 1.25-2.25 (Disagree), 2.25-3.25 (Neutral), 3.25-4.25 (Agree), and >4.25 (Strongly Agree) (Table 4). The responses reveal pronounced inconsistency in the daylighting conditions. When asked whether the lighting was uncomfortably bright, 25.9% strongly agreed, and 46.4% agreed, evidence of glare problems associated with the large 1800 mm × 1,200 mm windows used to serve the deep studio plan. At the same time, 25.9% strongly agreed, and 47.3% agreed that the lighting was uncomfortably dim, indicating underlit zones further from the façade. This contrast is reinforced by the finding that 28.6% strongly agreed and 44.6% agreed that daylight was unevenly distributed, and 18.8% strongly agreed and 39.3% agreed that they needed lanterns or spotlights even at noon.

Perceptions of adequacy clearly varied with location in the room. Near the windows, 42.0% strongly agreed, and 47.3% agreed that daylight was sufficient, whereas at the center of the studio, 35.7% strongly agreed and 36.6% agreed that daylight was inadequate. The non-uniformity of daylight was further confirmed by reported daytime use of artificial lighting (15.2% strongly agreed, 44.6% agreed). Overall, 17.9% strongly agreed, and 35.7% agreed that daylight provision in the studios was inadequate. Satisfaction ratings reflect these issues: only 16.1% were very satisfied and 31.3% satisfied, while 21.4% were neutral, 25.9% dissatisfied, and 5.3% strongly dissatisfied, meaning over half of the respondents (53%) expressed dissatisfaction. Taken together, these results show that visual comfort in the existing studios is highly dependent on seating position relative to the windows, with excessive brightness and glare near the façade and insufficient illuminance toward the interior, highlighting the need for a more balanced daylighting strategy.

The simulation began with the base case model, replicating existing studio parameters to validate lighting measurements. Comparing simulation results with measured data strengthens validity and reliability. The sky conditions applied in the simulations were chosen to match the actual conditions observed during the field experiments, with clear skies recorded in the morning and midday, and overcast skies in the afternoon. Figures 3a–c illustrate illuminance level simulation contours showing three different experiments. Surface reflectance impacts lighting levels significantly, and this simulation used standard reflectance levels recommended by IESNA (2011), incorporating glazing characteristics such as reflectance, transmission, refractive index, and material type (Table 2).

When comparing measurements with DiaLux Evo simulations, it's essential to account for methodological errors. Yang (2004) estimates measurement errors between 10% and 15%, while Willemsen and Wisse (2002) report errors as high as 20%. The comparative analysis showed percentage differences remained within the acceptable <20% margin, with exceptions at point G (experiment 1), points A and B (experiment 2), and point C (experiment 3), where discrepancies slightly exceeded this threshold. Table 5 provides a comparative analysis, showing full-scale measurements, DiaLux Evo simulations, and percentage differences. Figures 4a–c show line graphs comparing experimental measurement points with simulation results. The graphs indicate that DiaLux Evo generally overpredicted illuminance levels by approximately 2–20%, although in certain cases the measured values exceeded the simulated results. These validation exercises confirm DiaLux Evo’s accuracy in predicting daylighting performance within the architectural design studio. Figures 5a–d present the 3D views indicating interior views within the DiaLux Simulation Environment, showing: a) The studio within the DiaLux Simulation Environment; b) Measurement Plane in HND II; c) Measurement Plane within DiaLux Environment; and d) Measurement Plane in ND II.

Several design alternatives were explored in conjunction with the base case to enhance illuminance levels and visual comfort (Table 6). The base case retained original studio openings, while Alternative one added high-level windows on the west façade. Alternative two extended these windows to the west and east façades, and Alternative three increased the east façade glazing to compensate for daylight loss from the verandah (Table 6 No. 5). Alternative four incorporated clerestory skylights (0.6 × 1.8 m), while Alternatives five and six used larger skylights (0.9 × 1.8 m and 1.2 × 1.8 m). The window-to-wall ratio (WWR) increased from 10% (base case) to 13.1%, 16.2%, 20.8%, 26.3%, 31.2%, and 36.2% across Alternatives 1–6, with the window-to-floor area ratio following a similar trend (Table 6). Figure 6 shows 3D views of the existing studio with a hipped roof and Alternative 6 with clerestory windows. Alternatives such as clerestory openings were included not as a prescribed or universally cost-effective solution, but rather to evaluate their performance in comparison with other options. Accordingly, a cost–benefit analysis is recommended before adopting any specific option.

The study assessed illuminance levels at measuring points (A to K). The base case had the lowest average illuminance at 152.2 lux. Alternative 1, with high-level west façade windows, increased illuminance to 251.5 lux, though brightness remained higher near windows and lower at the studio center (points D, E, F, G). Alternative two added high-level windows on both façades, raising illuminance to 294.2 lux. Alternative three increased east façade glazing, improving illuminance to 318.7 lux, surpassing the 300 lux classroom standard but below the 500 lux studio requirement. Alternative four introduced 0.6 × 1.8 m clerestory skylights, raising illuminance to 433.4 lux. Alternative five expanded skylights to 0.9 × 1.8 m, achieving 534.4 lux, though some central points remained below 500 lux (Table 7). Alternative 6, with 1.2 × 1.8 m clerestory skylights, increased illuminance to 652.9 lux, meeting the 500 lux requirement across all points. The illuminance contours for Alternatives A1–A6 demonstrate the impacts of various daylighting strategies (Figure 8a).

Building orientation is a key driver of indoor illuminance and visual comfort in passive daylighting strategies. Daylight levels in interior spaces depend not only on the position and size of openings, but also on how the building is oriented relative to the sun’s path. In this study, orientation analysis was undertaken primarily to isolate the daylighting effect of verandahs, a common regional feature typically extending along one of the longer façades. Although orientation is widely recognized as a major determinant of daylight availability and distribution, the specific influence of verandahs on interior illuminance patterns and visual comfort remains underexplored. To address this gap, the simulations focused on building form and verandah configuration, while excluding external obstructions such as trees and neighboring buildings. On the actual site, trees are located along the shorter façade without windows and therefore have a negligible impact on the tested spaces. This modelling choice removes confounding shading effects and allows observed daylight outcomes to be attributed more clearly to orientation and verandah geometry, strengthening the inferences drawn about their roles in daylight performance and occupant comfort.

Eight orientations were examined, combining the main cardinal directions with verandah placement, to evaluate daylight distribution in the design studios. While four orientations would be sufficient for a fully symmetrical façade, the presence of a verandah on the front façade, typical of Nigerian studio buildings, necessitated a full set of eight cases to capture asymmetrical daylight responses. Figure 7 summarizes these orientations, including labels, azimuth angles, and key characteristics. The verandah’s position relative to the glazing significantly affects indoor daylight levels, justifying this more comprehensive orientation analysis. For the existing base-case studio, the illuminance levels for all eight orientations were analyzed to assess orientation-related daylight performance. Average illuminance values ranged from 147.7 to 180.7 lux, well below the 500 lux recommended standard (Table 8). Since no orientation of the existing configuration delivered adequate daylighting, the results clearly indicate the need for design modifications, particularly adjustments to window position, size, and/or verandah treatment, to achieve acceptable daylight performance in the studios.

The daylighting performance of Alternative six was evaluated to assess the impact of orientation on visual comfort. Among the eight orientations, Orientation 7 (O-7) at 270° produced the highest average illuminance (1,271.3 lux), significantly exceeding the 500 lux target (Table 8). In this configuration, the longer studio façade without a verandah faces south, aligning with the tropical sun path and receiving maximum solar radiation. While this enhances daylight availability, the elevated illuminance levels can contribute to overheating, thermal discomfort, and glare. Orientation 6 (O-6) at 225° recorded the second-highest illuminance, with its southeast-facing façade receiving substantial solar exposure. Orientations 3, 2, 8, 5, and one followed in descending order, and all except Orientation one achieved higher illuminance than the base-case orientation of Alternative 6. The simulations also showed that positions D and H consistently recorded lower illuminance than other measurement points in the studio. Position D is located at the room center, farther from the primary daylight apertures, while Position H is near façade openings that are partially shaded by the verandah. In contrast, points adjacent to façade openings without a verandah generally maintained higher illuminance across most orientations, highlighting the shading impact of the verandah. Figure 8b presents the illuminance contour plots for the simulated best-case alternatives (0°–315°), illustrating how daylight distribution varies with orientation.

The influence of glare on alternatives and daylight measures is pivotal for visual comfort, as it is affected by direct light on interior surfaces. In naturally lit buildings, window openings dictate light distribution, fluctuating with the sun’s position, building geometry, and time of day. Areas near windows often encounter glare discomfort. This study evaluated the glare index at multiple studio locations. The research used the supplied Daylight Glare Probability (DGP), a linearized version of the comprehensive DGP model (Wienold and Christoffersen, 2006), for assessing glare risk based solely on vertical illuminance (Ev) at eye level (Equation 1). Although this simplification assumes a “typical” glare source and is less precise than the full DGP, it is useful for comparing design alternatives. A study by Jakubiec and Reinhart (2011) determined that Daylight Glare Probability (DGP) provides the most credible results in examined spaces and lighting conditions, as it is based on contrast and total vertical eye illuminance, while other metrics rely entirely on contrast. DGP ≈ 5.87 × 10 − 5   · E v + 0.16 (1)

The DGP acceptability metrics (Jakubiec and Reinhart, 2011) classify daylight glare as imperceptible (no visual discomfort) when the DGP is less than 0.3, perceptible when it ranges between 0.3 and 0.35 (noticeable but tolerable glare), disturbing when it lies between 0.35 and 0.4 (disruptive glare; affects comfort), and intolerable when it exceeds 0.45 (severe glare; visual discomfort).

The analysis of Daylight Glare Probability (DGP) reveals consistent trends in visual comfort performance across all simulation scenarios. The results indicate that glare levels remain largely within acceptable limits, particularly in design alternatives that integrate daylight-enhancing strategies such as clerestory openings, high-level windows, and optimized orientations. In the study, which compares different design alternatives, the DGP values across all positions remained below the threshold of 0.35, classifying them as imperceptible glare levels, suggesting that each alternative, including the base case, performs well in managing daylight glare, which is due to careful daylight integration and moderate illuminance levels. Similarly, in terms of various orientations of the existing building and the best case, similar results were observed. Despite slight variations in illuminance due to orientation changes, DGP remained in the imperceptible range across all positions. This highlights that orientation alone, within the range tested, does not significantly impact glare perception under the modeled conditions.

Furthermore, the study analyzed Daylight Glare Probability (DGP) across various times of the day, revealing a significant range of variation. While most time slots exhibited imperceptible glare levels, a notable increase in glare was observed during the late afternoon, particularly around 5:00 p.m. (Figure 9a), where DGP values occasionally surpassed 0.40. These readings were classified as “disturbing” or even “intolerable” at specific positions, indicating a temporal vulnerability in visual comfort. This finding highlights the necessity for targeted glare mitigation strategies, such as louvres, automated blinds, or dynamic glazing systems, during critical hours of the day. In contrast, the analysis of seasonal variation demonstrated that DGP values remained consistently below critical thresholds throughout most of the year. Even during periods of high solar intensity, such as the summer solstice (21 June) and winter solstice (22 December), glare levels across most positions remained within the imperceptible range, indicating a robust design response to seasonal shifts in daylight availability.

The analysis of the different design alternatives revealed a clear increase in glare intensity from the Base Case to Alternative 6. The Base Case consistently remained within the imperceptible glare category, whereas Alternatives five and six showed elevated glare levels, especially at positions A, B, and C, which are closest to the window openings and frequently reached the disturbing glare range. This pattern reflects a typical daylighting trade-off: increased daylight penetration enhances visual performance and reduces reliance on artificial lighting but simultaneously heightens glare risk, highlighting the need for passive or active glare control measures in high-performance daylighting strategies. The DGI classification across orientation scenarios further confirmed the strong influence of orientation on glare performance. Several measurement points experienced intolerable glare (DGI ≥ 25) for orientations between 45° and 315°, particularly in the best-case design alternatives with higher daylight illuminance. These findings emphasize the orientation-dependent nature of glare, where solar path, façade exposure, and window configuration collectively shape visual comfort outcomes. In contrast, some positions under 0°, 135°, and 180° maintained DGI values within the imperceptible range, highlighting the importance of careful orientation and façade design in achieving a balance between sufficient daylight and acceptable glare levels.

Finally, the assessment of seasonal DGI variation (Figure 9b) reinforces these observations. Glare levels remained largely imperceptible during the equinoxes (21 March and 23 September) and at the summer solstice (21 June. In contrast, a pronounced increase in DGI occurred during the winter solstice (22 December), when several positions, particularly those closest to the glazing (A, B, and C), reached intolerable glare levels. This outcome is likely driven by the lower solar altitude and deeper penetration of direct sunlight into the studio during winter. This seasonal peak in glare underlines the importance of dynamic or adaptive glare control strategies (e.g., adjustable shading, blinds, or electrochromic glazing) that can respond to changing solar geometry throughout the year, maintaining acceptable visual comfort while preserving the daylighting benefits of the façade design.

Daylight illuminance in indoor spaces naturally varies with solar radiation and sun position. In this study, the simulation period extended from 7:00 a.m. to 6:00 p.m., with illuminance recorded at hourly intervals, capturing the full daily cycle of daylight and allowing a comprehensive evaluation of both glare and illuminance performance in morning and afternoon periods. For the best-case configuration (Alternative 6), a more detailed analysis was conducted from 6:00 a.m. to 6:00 p.m. At 6:00 a.m., no daylight contribution was observed, and at 7:00 a.m., the illuminance was still below the 500 lux target (Table 9). Illuminance levels increased and peaked around 9:00 a.m., then decreased toward midday as the sun’s higher altitude and changing incidence angle reduced daylight contribution through the façade. From 1:00 p.m. onward, illuminance began to rise again, reaching its highest values at 5:00 p.m. before declining toward sunset at 6:00 p.m. This diurnal pattern highlights the strong influence of solar geometry on indoor daylight availability and highlights the need to consider time-of-day effects when assessing daylighting performance.

The illumination uniformity ratio describes how evenly light is distributed across a space and is a key determinant of visual comfort. CIBSE recommends a target uniformity of 0.7, while BREEAM (2008) defines acceptable ranges of 0.30–0.54 (morning), 0.45–0.66 (midday) and 0.50–0.56 (afternoon), all above the minimum requirement of 0.4. For classrooms, a ratio of 0.4 is generally acceptable, whereas studios undertaking intensive visual tasks are recommended to achieve 0.6–0.8 (DfEE, 1999; CIBSE, 2011; EN 12464-1, 2011; BRE Global Ltd, 2014). In this study, uniformity was calculated using two indices: U1 (minimum/average illuminance) and U2 (minimum/maximum illuminance). The best-case configuration (Alternative 6) achieved 0.8 (U1) and 0.7 (U2) (Table 10), placing it at the upper end of the recommended range for studio environments. Across all eight orientations, uniformity ratios remained between 0.4 and 0.8 (Table 10; Figure 10a), satisfying classroom criteria and, in many cases, approaching studio standards. For the orientation with the highest average illuminance (270°), U1 and U2 were 0.4 and 0.7, respectively, indicating an acceptable balance between overall light level and distribution in an educational context.

Temporal analysis revealed that the illumination uniformity ratio varies over the day. Uniformity remained within acceptable limits for most hours, with two notable exceptions. Between 2:00–3:00 p.m., U1 dipped slightly below the preferred threshold, although U2 stayed within acceptable bounds. At 5:00 p.m., the situation reversed: U1 remained acceptable (0.5), while U2 fell to 0.35, likely reflecting strong directional daylight and contrast associated with the lower solar altitude before sunset (Table 10; Figure 10b). Despite these brief deviations, the overall uniformity remained generally satisfactory throughout the day, supporting the effectiveness of the proposed daylighting strategy in maintaining visually comfortable conditions in the design studios.

This study considered six characteristic dates to capture the combined effects of seasonal solar geometry and local climatic variation on daylighting performance. Four of these dates correspond to the key astronomical reference days of the year, 21 March (Vernal Equinox), 21 June (Summer Solstice), 23 September (Autumn Equinox), and 22 December (Winter Solstice), when the sun’s path and altitude represent the principal seasonal extremes and transitions. The equinoxes provide representative “mid-season” conditions with roughly equal day and night, while the solstices represent the highest and lowest solar paths, which are critical for assessing the range of daylight penetration and potential glare. In addition, two climate-specific dates were selected: 15 April (hottest month and onset of the rainy season) and 15 August (rainiest month), to reflect local extremes in temperature and cloud cover that may alter daylight availability. Together, these 6 days offer a compact but representative set of conditions for evaluating annual daylight behavior in the studios of the study area.

The corresponding average illuminance levels are summarized in Table 11. Among these periods, the Winter Solstice (22 December) produced the highest average illuminance (977 lux), as the sun’s lower altitude and tilt toward the south allowed deeper penetration of direct solar radiation into the studio. The Autumn Equinox (23 September) yielded the second-highest illuminance, benefiting from a favorable balance between solar height and façade exposure. By contrast, the Vernal Equinox (21 March) and Summer Solstice (21 June) recorded more moderate values of 685 lux and 692 lux, respectively, reflecting higher solar altitudes and reduced direct penetration into the interior. The hottest month (15 April) and the rainiest month (15 August) showed similar average illuminance levels (676 lux and 674 lux), indicating that, despite climatic differences in temperature and cloud cover, the overall daylight availability in the studio remained relatively stable across these two locally significant periods.

From a design perspective, these seasonal patterns highlight the need for daylighting and shading strategies that perform robustly across the full annual range of solar conditions. The high illuminance levels observed at the Winter Solstice and Autumn Equinox suggest an increased risk of glare and local overheating during cooler seasons when deeper sun penetration occurs, whereas the more moderate illuminance at the Summer Solstice and during the hottest and rainiest months points to a different balance between daylight sufficiency and solar control. Effective façade design, combining orientation, glazing properties, and fixed or adaptive shading, must therefore address not only peak summer gains, but also winter and shoulder-season conditions, ensuring adequate daylight while mitigating seasonal glare and thermal discomfort throughout the year.