Photoluminescent Materials: From Visual Gimmick to Infrastructure

Some materials remain "invisible" until the precise moment and context arrive. Photoluminescent materials—colloquially known as "glow-in-the-dark" materials—are a prime example: in daylight, they tend to appear greyish and mundane to the point of being almost unnoticeable, but in the dark, they reveal a unique material property that evokes wonder. Their luminous capacity typically stems from a physical phenomenon called photoluminescence: the ability to absorb light energy and release it back. When the light emission continues passively even after the original light source has disappeared, the phenomenon is termed phosphorescence.

The technology underlying these materials or pigments is not new, but the chemical compounds composing them have undergone a significant evolution to remove toxic or radioactive components that were commonly used in the past. Today, most modern applications are based on stable crystals of strontium aluminate.

Safety and emergency signs that glow in the dark thanks to an embedded photoluminescent pigment. Halperin Printing. Photo: Efrat Barak

The Dynamic Transition from Experience to Infrastructure

In the everyday consumer space, phosphorescent materials are often identified with novelty pop products of a decorative or playful nature, such as wall stickers or party accessories. In these contexts, the material property functions as a visual effect, aiming to generate sensations of magic, wonder, or amusement.

However, this exact same material property provides a completely different function when embedded within an operational system. For instance, in emergency signaling and signage within protected spaces or shelters, these pigments provide a critical infrastructural response that does not depend on the power grid. In this type of application, the material is evaluated not by its aesthetic value, but by its ability to grant users a sense of security, orientation, and control over the space during extreme situations. In certain cases, one can also see applications that combine the aesthetic and experiential values of these materials with their functional values.

The "Smart Highway" project, launched by Dutch designer-artist Daan Roosegaarde in 2012 in collaboration with the infrastructure company Heijmans, proposed to combine these capabilities and values on a macro-infrastructural scale. Roosegaarde, who had previously explored the relationship between light and movement in public spaces through experiential installations (such as the interactive installation DUNE exhibited at the Design Museum Holon), attempted to translate traditional asphalt markings into a passive, glow-in-the-dark system that replaces street lighting.

After a short period of operation and despite positive feedback, the pilot encountered durability and wear challenges, as well as a lack of adaptation to local climate conditions, which led to its discontinuation. Nevertheless, its extensive exposure turned it into a benchmark within a series of experimental projects worldwide that used phosphorescent materials for road markings, raising fundamental questions about how we evaluate innovative material solutions.

Economic and Systemic Analysis of Material Alternatives

For nearly two decades, a wave of experiments worldwide has utilized glow-in-the-dark materials to mark road and highway systems, including in Australia, Ireland, and Malaysia. There are several safety, economic, and environmental justifications for this: first, the assumption is that road markings using glow-in-the-dark paint improve the spatial orientation and sense of safety of various road users, similar to its use in emergency signage. Second, using a safety marking method that does not require the installation and operation of complex infrastructures, such as electricity, is fundamentally cost-effective and can also provide a solution in areas where implementing complex infrastructure is impractical or unfeasible. Finally, reducing energy consumption (electricity) and mitigating the light pollution generated by road infrastructure reduces the impact on the natural environment and supports biodiversity.

One example of such a pilot carried out in recent years was conducted in 2023 in the Hulu Langat district of Malaysia. It is interesting not only because of its initial potential, which was perhaps greater than that of the Dutch pilot, but because it illustrates a common failure in decision-making processes and feasibility testing for new technologies.

Road marking using photoluminescent paint. Credit: LuminoKrom

The experiment in question was born out of a tangible safety need in a country filled with rural, dark, and unlit road segments characterized by a high accident rate. In such areas, passive solutions based on light reflection, such as "cat's eyes" (also known as Raised Pavement Markers - RPM or road studs), provide only a partial response because the roads are also heavily used by pedestrians or cyclists, who do not "produce" light themselves and therefore generate no reflected light. Consequently, the authorities decided to apply a special photoluminescent paint to the asphalt that passively emits light during hours of darkness. The project received enthusiastic responses, both from residents and from other authorities in the country, but it was stopped after about a year. The primary reason for cancellation was the high cost of the glow-in-the-dark paint, which costs dozens of times more than standard road marking paint.

From a strategic design innovation perspective, this comparison between the paints is flawed. Standard marking paint does not produce independent visibility in the dark and does not change the safety equation in an unlit area, making it an irrelevant functional alternative for comparison. To make a practical and informed decision, it would have been correct to compare the cost of the special paint to the cost of solutions that actually provide enhanced safety on these roads, such as an electricity-based lighting system. In such a scenario, the decision would likely lean toward the glow-in-the-dark paint, as electrical lighting introduces additional costs for infrastructure deployment, light poles, ongoing maintenance, and continuous energy consumption. Yet, in the case of the pilot in question, the decision was made—at least for now—to halt without providing an improved safety solution. In this context, it is also interesting to mention the external costs of abandoning the project, meaning the health and social costs of traffic accidents. Such a comprehensive evaluation, which takes into account the full costs of the decision, might have altered the business viability and presented the use of the innovative material as an efficient and affordable solution.

Photoluminescent Materials, the Limits of Darkness, and Environmental Context

When looking at groundbreaking developments and long-term costs, it is worth remembering that evaluating the performance of a specific material or solution is not disconnected from the human and ecological system in which it operates; therefore, not every application of an innovative solution is necessarily the right one. For example, in recent years, various studies and experiments have been published dealing with the genetic engineering of plants, turning them into a kind of plant-based firefly by introducing biological lighting mechanisms (bioluminescence) to create "lighting from nature." But in the context of such deep intervention in the genetics of living organisms (yes, plants are living organisms) and the potential impacts of integrating genetically engineered living things into the natural environment, much remains unknown, and what is already known raises concern among experts.

This insight aligns with foundational principles in modern ecology, which argue that because nature operates as a massive system where every element is linked to another in complex interrelationships—most of which are unknown to us—using a healthy dose of humility in any case of human intervention in the natural environment is probably the right thing to do. Furthermore, regarding nocturnal lighting, scientific literature has already proven that many species of animals and plants depend on regular cycles of darkness for their proper biological activity, and the introduction of constant light sources can generate significant environmental damage whose results are revealed over time. This phenomenon, termed light pollution, can also impair various aspects of human life, such as sleep quality and even leisure experiences.

For this reason, out of an active intention to reduce light pollution and preserve the local biodiversity in Mitzpe Ramon, it was declared several years ago as an International Dark Sky Park. In practice, this means the maximum reduction of artificial lighting within the crater area and its surroundings. In our context, the application of photoluminescent aggregates within concrete castings and pedestrian pathways in the public space—as was done even prior to the declaration along the walking path in the desert sculpture park in Mitzpe Ramon—offers a solution. Beyond its impressive visual effect, it highlights the complexity between perceiving a material as a "gimmick" and integrating it into complex functional systems, providing a response that respects the nocturnal environment to a certain degree.

Immediately after sunset, the aggregates embedded in the concrete of the path in the Desert Sculpture Park in Mitzpe Ramon begin to glow. Photos: Efrat Barak

Indeed, the after dark visit to the sculpture park shows that integrating the luminous aggregates into the walking path does not compete with the darkness or illuminate the space artificially; it coexists alongside it. The light-emitting stones mark the terrain gently, allowing basic human orientation without disrupting the ecological balance of the reserve. Compared to the results of the pilots conducted on roads, it appears that it is precisely the controlled integration of photoluminescent materials in spaces characterized by a slower pace of movement and a more human scale, such as walking paths, bicycle lanes, or parks, that yields the greatest benefit from the unique properties of these materials.

Material innovation does not always require the synthesis of a new polymer or a laboratory breakthrough. Nevertheless, it will be interesting to see if a new material emerges that proves durable and effective for glow-in-the-dark road markings that actually work. For that to happen, one must begin with a deep understanding of the material's properties, from its passive illumination capacity to its resistance to wear by car tires, including how the paint can be applied and maintained by crews and its adaptation to local climate conditions.

Everything depends on placing capabilities and possibilities within the correct system. When we properly define economic comparison terms and understand the environmental implications of the application, new and familiar materials alike can generate entirely new value and signal practical solutions for tomorrow's challenges.

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