Glare from Solar Modules: Causes, Risks, and Solutions

Glare from photovoltaics occurs when sunlight is specularly reflected on the module surface at certain angles and appears significantly brighter in the field of view than the surroundings. Although modern PV modules are optimized for high light absorption, they physically always reflect a portion of the incident light. In residential environments, glare is often temporary but is perceived by those affected as very unpleasant and can significantly reduce living and recreational quality. In safety-critical areas such as roads, railways, or airports, the risk is paramount—here, glare effects can be safety-relevant and must be consistently avoided.

With the rapid spread of photovoltaic systems (PV) on roofs and facades, one issue is increasingly coming into focus for planners, neighbors, and authorities: glare caused by reflection-related light emission. What was often unproblematic with conventional south-facing roof installations is increasingly leading to legal disputes with modern east-west systems or facades.

What is glare? A definition

Glare is a visual impairment that occurs when a light source or reflection in the field of view has a very high luminance compared to the surroundings. Depending on the situation, it is perceived as unpleasant, disturbing, or painful—and is therefore partly subjective. Two main forms are distinguished:

  • Disability glare (physiological glare): This involves a measurable impairment of visual performance. Scattered light in the eye reduces contrast on the retina so much that objects can no longer be reliably recognized (important in road and air traffic).
  • Discomfort glare (psychological glare): This form is perceived as subjectively disturbing, distracting, or tiring. There is no measurable deterioration of visual acuity, but well-being (e.g., in the living room) is significantly impaired. 

The physical fundamentals: Why do modules cause glare?

Modern low-glare solar modules are usually equipped with anti-reflective coatings. However, such coatings are primarily optimized to maximize yield—especially for perpendicular light incidence. Due to their smooth nature, these anti-reflective coatings are inherently hardly effective against glare effects, and solar modules often reflect well over 1 million cd/m² at shallow angles of light incidence.

Specular vs. diffuse reflection

The reflection of light on different surfaces can be divided into 2 categories:

  • Specular reflection: Light is reflected at a precise angle, like on a mirror (angle of incidence = angle of reflection). This mainly occurs on smooth glass surfaces.
  • Diffuse reflection: The rougher the glass surface, the more the light is scattered in different directions upon reflection. This significantly reduces the luminance perceived by the observer.

Since diffuse reflection distributes light over a wider angular range, diffusely reflecting surfaces appear similarly bright from different viewing directions. In contrast, specular reflection produces extremely high brightness at the reflection angle. Typically, surfaces exhibit a reflection behavior that is a combination of specular and diffuse reflection.

The more diffusely a surface reflects, the less likely glare is to occur for these reasons. Besides reducing the reflection coefficient, this is the most important approach for developing low-glare (anti-glare) surfaces.

Luminance comparison

For assessing the glare effect of solar modules, three parameters are particularly decisive:

  • Luminance (cd/m²) of the reflecting surface
  • Geometry (angle of incidence and observation)
  • Duration and frequency of the reflection

While geometry determines whether a reflection is visible, luminance determines how strongly the reflection is perceived.

Typical orders of magnitude help to classify:

Light source / surface Luminance in (approx.)
Sun (noon) 1,600,000,000 cd/m²
Blue sky 5,000 - 10,000 cd/m²
PV module (standard, with anti-reflective coating) >100,000 cd/m²
Limit value Federal Highway Authority 30,000 cd/m²

For comparison: The ambient luminance in a typical landscape usually ranges only from a few hundred to a few thousand cd/m².

Reflections on standard PV modules can thus be several orders of magnitude above the ambient luminance. The decisive factor is the directional (specular) reflection, where part of the sunlight is concentratedly mirrored in a specific direction.

This strong luminance contrast is primarily responsible for the perceived glare effect – especially in traffic or neighborhood contexts.

Where does glare occur most frequently?

Glare occurs when a smooth module surface reflects sunlight specularly (mirror-like) directly towards an observer. Crucial factors are the sun’s position, module orientation, surface structure, and the observer’s position.

It becomes critical especially in the following constellations:

  • Non-south orientations: Due to the price decline of PV modules, increasingly east, west, and even vertical facade surfaces are being covered. These surfaces often reflect light at angles that do not occur with classic south-facing orientation and are therefore frequently not considered in planning.
  • Hillsides: Glare effects also occur disproportionately often in densely built hillside areas. Here, even south-facing PV systems can cause glare.
  • Large glass facades: Well-known examples from architecture demonstrate the power that directed glass reflections can develop: For instance, the glass facade of the University Library Freiburg caused strong glare at low sun angles, and the London skyscraper “Walkie-Talkie” became a burning glass due to its concave shape.
  • PV systems near sensitive infrastructure: PV systems near highways, railway lines, or airports are subject to particularly high safety requirements, as even short-term glare events can be critical here.
  • PV systems in neighborhoods: If a neighbor is dazzled by a PV system, it often destroys the neighborhood relationship – frequently leading to lengthy disputes with high legal, expert, and court costs.

Why glare is becoming a more frequent issue today

In the past, south-facing rooftop systems dominated. Reflections were mostly directed uncritically into the sky or onto the ground. Today, east, west, and facade surfaces are increasingly being equipped. At low sun angles, reflections can thus hit neighboring buildings or traffic areas horizontally. In densely built-up areas, systems also come closer to sensitive sightlines – making glare a more frequent issue. Whether a module actually causes disturbance ultimately depends on its surface: while smooth glass reflects light harshly like a mirror, textured surfaces can scatter light rays and significantly reduce the glare effect.

Where are low-glare or glare-free solar modules used?

Low-glare solar modules are used wherever reflections trigger special requirements – whether for safety reasons, approval feasibility, or to avoid neighborhood conflicts.

  • Airports: At airports, the reflection effect of PV systems is evaluated particularly critically because reflective glare can impair pilots during approach or air traffic controllers in the tower. A prominent example is the case at Amsterdam Schiphol Airport, where panels had to be removed due to dazzling reflections to avoid endangering flight operations and safety, and therefore the Federal Aviation Administration in the USA requires specific glare analyses before solar modules may be installed closer than certain distance zones.
  • Traffic routes: PV systems along highways, railways, or other traffic hubs are also subject to special testing obligations. In Germany and other countries, operators must submit a glare report demonstrating that reflections do not distract or endanger road users (see Key points paper of the Federal Highway Research Institute (external link)). Such situations often require the use of low-glare solar modules with significantly reduced luminance.
  • Residential areas: Even in residential areas, glare freedom is often not merely a matter of comfort but a building code requirement: According to emission control guidelines, a system must not glare residents to such an extent that significant disadvantages or nuisances arise. Such requirements can become conditions in approval procedures—especially for ground-mounted systems near residential areas.

The legal situation

Worldwide, there is no uniform definition or binding standard for assessing glare caused by photovoltaic systems. The evaluation varies by country—sometimes through aviation regulations, sometimes through emission control law or civil law provisions. Uniform international limit values do not yet exist. 

For a detailed analysis of the current limit values and legal updates for 2026, please read our article on PV glare & law.

USA

In the United States, regulation follows a two-pronged approach. While civil law aspects often prevail in general areas, strict glint-and-glare analyses are mandatory in airport environments. Here, the Federal Aviation Administration (FAA) ensures that reflections do not impair pilots' visibility during approach or the work in the air traffic control tower (ATCT).

Europe

In the EU, glare is generally addressed through national emission control and approval procedures. There is no specific EU regulation. Instead, authorities rely on guidelines, reference values, and expert assessments. The key question often is whether there is a "significant nuisance" or a risk to traffic safety.

Germany

The assessment is mainly based on the LAI guideline (Länder Committee for Immission Control, external link). Glare can be considered "significantly disturbing" if it affects a protected space for more than 30 minutes per day or 30 hours per year, for example.

For installations near federal highways, additional requirements from the Federal Highway Authority apply, especially regarding permissible luminance levels in traffic-relevant fields of view (see Key points paper of the Federal Highway Authority (external link)).

Austria

The practice is comparable to Germany. Glare is assessed by expert reports during the approval process or in case of complaints. There are no independent legal limit values, but established evaluation procedures exist.

Switzerland

In Switzerland, evaluation methods have been scientifically advanced, among others at the Bern University of Applied Sciences. Simulations of duration, intensity, and frequency of glare events are an integral part of the professional assessment here. 

Assessment and solutions: How to deal with glare?

If there is a risk of glare, it is ideally addressed already in the planning phase. The earlier geometry and surroundings are considered, the easier it is to avoid later conflicts.

1. Simulation and expert report

Whether and when glare occurs can now be reliably simulated. Using specialized software, the sun path, module geometry, and possible receptors (e.g., residential windows, roads, or towers) are analyzed. This allows estimating whether critical reflections occur and how long they last.

Specialized software can calculate the exact sun path and reflection geometry. Common tools include:

2. Structural and technical solutions

If a relevant glare effect is identified during planning or an expert report, various solutions are available. Which measure is appropriate depends largely on whether the system is still in the planning stage or already installed.

  • Adjustment of geometry: Changing the tilt angle or orientation can influence the direction of reflection. This option is usually most effective during the planning phase but is only limitedly practical for existing installations.
  • Visual shielding: Hedges, trees, or structural elements such as glare protection fences can interrupt the direct line of sight. These measures do not change the reflection itself but prevent it from reaching the affected area.
  • Special modules: Modules with satin-finished or deeply textured front glass scatter light more diffusely. This can reduce specular reflection and lower the luminance in the critical field of view. Due to significant differences in light scattering properties, module-specific test reports on reflected luminance should always be used to assess the suitability of a particular module.
  • Retrofit: For modules with conventional glass surfaces, the glare effect can be specifically reduced. One option is to equip the module front with an Anti-glare film. This film is applied directly to the front glass, is manufacturer-independent for different module formats, and changes the optical properties of the surface. Due to its microstructured design, the incident light is scattered more diffusely, which reduces specular reflection and lowers the luminance in the critical field of view.

Conclusion

Glare is caused by high specular luminance at the reflection angle of smooth module surfaces. The geometry, intensity, and duration of the reflection are decisive. However, glare risks can be effectively reduced through appropriate planning, simulation, and adapted optical surfaces.

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