- Understanding the impact of glare on human perception
- Measuring glare comfort: essential metrics for accurate analysis
- Advanced glare analysis tools: tailored solutions for precision lighting
- Applications for the building and automotive industries
- Conclusion - Glare analysis tool for comfort optimization
Understanding the impact of glare on human perception
Glare analysis is a new feature in OceanTM 2024 as a part of the human vision module. This module, available as a post-processing calculation, can analyse the brightness levels, distribution of light sources and contrast in the scenes from a fisheye camera and evaluate glare level in terms of comfort of perception.
Glare is a visual condition resulting in either discomfort or reduced visibility. There are two categories of glare: disability and discomfort glare.
- Disability glare is a physiological phenomenon caused by light scattering in the eye, leading to reduced visual performance. It can be characterized by a threshold perception.
- Discomfort glare is a psychological phenomenon that affects visual comfort. It does not directly impair visibility but creates a distracting or unpleasant experience for the viewer. As it is subjective, it is harder to quantify.
Discomfort glare is the subject of the present article. Currently, there is no theoretical framework that fully apprehend this type of glare. Yet, discomfort glare is a major issue for lighting and daylighting design, leading to several metrics being developed to quantify it.
A next article presents our EGSR 2025 paper on Ocean™’s glare simulation workflow, with downloadable scenes and results from real-world case studies.
Measuring glare comfort: essential metrics for accurate analysis
Most models for assessing discomfort glare have been conceived under different experimental conditions. Therefore, an objective comparison of glare quantification models is challenging. There is no consensus on a universal criterion measure, but there is a general agreement on the factors that cause glare: Ls – the luminance of the glare source (cd/m2), Lb – the background mean luminance (cd/m2), ωs – the solid angle of the glare source (str), Pi – the position index of the glare source, (ratio of luminance at an arbitrary position to the luminance on the line of sight that causes the same glare sensation. Position index is a perception model of our retina. In the central retinal field fovea centralis, the density of light-sensitive receivers is significantly higher than in the outer region), Ev – the vertical illuminance at eye level (lux).
To constrain our glare analysis to the most relevant metrics, we choose to focus on the following three indices, that are appropriate for our applications: UGR (unified glare rating), DGP (daylight glare probability) and GR (glare rating). It is accepted to use these indices for different specific conditions: UGR – for indoor analysis with artificial lightning; DGP – for indoor analysis with daylight conditions and direct sun; GR – for outdoor workplace condition evaluation.
Advanced glare analysis tools: tailored solutions for precision lighting
Optimal fisheye projections for different scenarios:
The use of a fisheye camera in glare analysis is imposed by the necessity to evaluate the large field of view of human eyes. Our glare analysis tool offers an advanced feature that supports four different fisheye camera projections—equidistant, equisolid, orthogonal, and stereographic—providing flexibility and precision for a variety of lighting and visibility assessments.
Each projection type has unique advantages depending on the project’s needs:
The equidistant projection keeps equal distances, making it ideal for applications where scale consistency is essential.
The equisolid projection, which balances area more effectively, is particularly useful for analysing illumination levels across larger spaces.
The orthogonal projection provides an undistorted field of view ideal for detail-oriented analysis.
The stereographic projection delivers a realistic panoramic view, used in architectural visualization to understand visual impact.
With these versatile fisheye projections, our glare analysis tool adapts to any lighting design project ensuring accurate, project-specific insights.
Furthermore, our glare analysis tool offers precise and adaptable evaluation through two key input parameters. First, users can set a threshold luminosity to differentiate glare sources from the background, defined either as a luminance value in cd/m² or as a contrast ratio.
Select ideal positioning models for accurate glare evaluation:
Second, a selection can be made between two positioning models, the Guth or Kim indices, for accurate evaluation of glare source position. The results are presented with a comprehensive global glare rating for the whole scene, along with a uniquely developed individual glare rating per-source.
They show how glare affects the observer from the entire scene and each light source, to help improve lighting design decisions based on reliable data.
A position index defines to weight the image of the glare source on the human retina according to its position. This position index is basically a perception model of our retina. Two position indexes are available in Ocean™:
- Kim position index was developed to quantify discomfort glare from light sources perceived by both eyes, particularly in the lower visual field, which is more sensitive to glare.
- Guth position index is the most common in glare analysis. In our tool, it is used for the half sphere above the line of sight, combined with Iwata position index for the half sphere below the line of sight.
Use color coding for clearer glare severity assessment:
To enhance the visual clarity of glare analysis results, Ocean™’s glare analysis tool uses color coding for glare sources, based on the calculated isolated glare rating for each source (Figure 1).
Figure 1: Outdoor scene simulation in Ocean™ with its glare map.
This color scheme has been developed to align with standard glare levels, allowing for straightforward recognition and assessment of the severity of glare from each source. Dedicated color is in accordance with colors in Figure 2.
Figure 2: Discomfort indices thresholds according to deBoer’s scale and their selected color codes.
See examples below of glare maps depending on the nature of light sources (Figure 3 & 4).
Figure 3: Indoor scene simulation in Ocean™ with its glare map using DGP indice.
Figure 4: Indoor scene simulation in Ocean™ with its glare map using UGR indice.
Applications for the building and automotive industries
Glare results from complex optical interactions such as light scattering, reflection, and refractive index variations that occur when light passes through or reflects off surfaces such as glass.
In the automotive industry, windshield glare can be intensified by factors like direct sunlight at low angles (figure 5), while reflections from interior surfaces can reduce visibility (figure 6).
Figure 5: Glare effect caused by direct sunlight at low angle.
Figure 6: Glare effect caused by reflections in the car cabin.
In architectural glazing, glare can lead to discomfort for occupants, in buildings with large glass façades that face direct sunlight. Different optical treatments and materials—such as anti-reflective coatings, tinted glass, and laminated layers—are applied to glass surfaces to control these effects by either diffusing light, reducing specific wavelengths, or altering surface reflections. These treatments impact glare metrics like UGR, DGP and GR.
The use of Ocean™’s Glare analysis tool, is a way to understand how each material affects these metrics, to make informed decisions that balance visibility, comfort and safety in applications ranging from automotive to architecture.
Conclusion - Glare analysis tool for comfort optimization
Our glare analysis tool calculates the three most relevant glare indices: UGR, DGP and GR. Additionally to the standard whole-scene glare rating, our tool includes a unique per-source glare rating feature. It allows to assess the specific impact of each light source on overall glare, offering detailed insights that support optimal lighting design solutions.
Glare analysis is a new feature in OceanTM 2024 that completes the human vision module. See our previous articles about OceanTM‘s human vision module:
Let's talk about your project
Read about our services & solutions or contact us for customized support:
Responses