Berlin, November 2025. The Falling Walls Science Summit likes to talk in grand terms: walls that should fall – in science, business, and society. But sometimes it’s not the big metaphors, but the small wavelengths that can change things: Deep-Ultraviolet light.

Ultraviolet light is increasingly being rediscovered as a versatile and powerful tool of modern technology. Many people think of sunburn, sunscreen, and warning notices when they hear the term. However, the Falling Walls Science Summit in Berlin showed that UV – more precisely: Deep UV and Far-UVC – is increasingly becoming one of the most exciting tools of modern photonics. Not only as “invisible light”, but as light with special powers: energetic enough to break chemical bonds, inactivate microbes, or stimulate atoms with extreme precision.

In the panel “Deep-UV Innovation: Shaping the Future of Photonics”, Michael Kneissl (TU Berlin, Chairman of the Board of Advanced UV for Life), Åsa Haglund (Chalmers University), Tanja Mehlstäubler (PTB), and Martina Meinke (Charité) discussed how advances in UV LEDs and UV lasers are enabling new applications – and why the leap into practice is not only a question of physics, but also of manufacturability, education, and public relations.

First of all: What is “Deep UV” anyway?

We know the rainbow spectrum: Red, Green, Blue. But below 400 nanometers, the ultraviolet begins. It is roughly divided into UVA, UVB, UVC, and “Vacuum UV”. The important point that Prof. Kneissl made clear right at the beginning: UV photons carry significantly more energy than visible light. Much more. Enough to break chemical bonds.

The distinction between natural UV light from the sun and artificial UV light from the laboratory is important. The sun emits UV – but our atmosphere filters out most of it, so that mainly wavelengths in the UVA and UVB range arrive at the ground. UV light from the sun is both useful (e.g. for vitamin D production) and dangerous (sunburn, increased risk of skin cancer).

These properties also explain why UV light – especially in technical applications – is so desirable: Where bonds can be specifically “broken”, it is possible to disinfect, measure, structure, or harden. Particularly interesting for controlled applications are those UV ranges that hardly occur in nature and therefore have to be artificially generated: UVC, Far-UVC, and even shorter-wave UV – summarized as Deep-UV.

From Mercury Lamps to Semiconductors: Why the Change is Happening Now

Many classic UVC applications are still based on mercury vapor lamps (typically at 254 nanometers), for example in water disinfection. They are established – but mercury is considered toxic and is increasingly being pushed back by regulations.

The panel therefore focused on alternatives: semiconductor-based UV LEDs and UV lasers. Something decisive is happening here. UVC LEDs are now commercially available and, according to the panel discussion, are already achieving wall-plug efficiencies of around 10 percent – with further potential for improvement. This sounds like an engineering detail, but it is a central “tipping point”: Efficiency (and service life) determine whether special technology becomes a scalable platform for broad applications.

In addition, there is a second lever: Semiconductors can be manufactured on wafers in large quantities. If the production volume increases, the prices fall – a mechanism that is well known from the classic LED world.

LED or Laser? Two Types of Light, Two Superpowers

Åsa Haglund explained the difference as follows:

• LEDs generate light via spontaneous emission. It is broadband, comes from many directions and has a “diffuse” effect.
  This is ideal when surfaces are to be illuminated – for example in disinfection, phototherapy or UV curing.
• Lasers generate light via stimulated emission. The result is a directed, narrowband and coherent beam – a precise tool that can also be modulated very quickly.
  This is particularly suitable for applications in which light is used in a targeted and controlled manner: spectroscopy, interferometry, lithography, 3D printing – and last but not least quantum technologies.

It is exciting that in the Deep-UV range, lasers often still exist as large, expensive systems today (such as excimer lasers or frequency-converted lasers). Haglund’s vision – and the direction of research – is a semiconductor laser that would be tiny, efficient, and potentially inexpensive. This would transfer Deep-UV lasers from the “laboratory class” to the “product class”.

Why is this so difficult? Because UV semiconductor materials (e.g. AlGaN systems) not only have to function well optically, but also electrically: For lasers, high-quality resonators and mirror structures are required, as well as reliable n- and p-conductivity (to allow electrons to “flow”), which is particularly challenging with these materials. However, Haglund emphasized that progress in material quality, mirror concepts, and injection mechanisms has recently increased significantly.

Quantum Computers & Atomic Clocks: When UV Light Becomes a Time Machine

Tanja Mehlstäubler from the Physikalische Technische Bundesanstalt brought the Deep-UV perspective from a world where precision is everything: metrology, atomic clocks, and quantum hardware.

A central point: As soon as atoms are ionized (ions instead of neutral atoms), important optical transitions shift towards blue and UV. For ion-based quantum technologies, laser wavelengths around 397 nm, 370 nm, 313 nm and other UV ranges become relevant.

But her real message was not that it was primarily about laser power. The bottleneck is often elsewhere: How does the light get to where it is needed with as little loss as possible? For scalable quantum processors, photonics must be integrated directly onto the chip – not as a large laboratory of mirrors and lenses, but as a miniaturized infrastructure of waveguides, modulators, and switches.

This is where it becomes particularly difficult in the UV range. Losses increase because surface roughness, material defects, and manufacturing limits have a greater impact. Mehlstäubler illustrated the problem: A powerful laser is of little use if only a fraction of the light arrives cleanly at the ion in the end.

Far-UVC in Medicine: Why “Deeper” Can Sometimes Be Safer

Martina Meinke from the Charité reversed a well-known perspective. In essence, she explained: In dermatology, the saying is usually “avoid UV”. And yet Far-UVC can help medically – precisely because it is absorbed more strongly than classic and natural UV light.

The key to this paradox lies in the geometry of life: The outermost layer of skin, the stratum corneum, consists of dead cells without a nucleus. If Far-UVC light is so short-wave that it is almost completely absorbed in this top layer, it hardly reaches the living cells underneath. Microbes on the surface (such as bacteria, viruses, or fungi), on the other hand, are small enough that their genetic material can be damaged. The basic idea is therefore: Hit germs, spare tissue.

Meinke classified this into two global problem areas:

1. Antimicrobial resistance (AMR): If antibiotics fail, new concepts are needed.
2. Pandemics: If viruses spread through the air and on surfaces, any technology that reduces the risk of infection is relevant.

The panel also discussed specific wavelengths: 222 nm (often from excimer lamps) is considered particularly “superficial” and is therefore suitable for air and room disinfection. 233 nm (as an LED approach) penetrates a little deeper. This is helpful because skin is microscopically uneven and germs do not only sit on a “smooth surface”.

A central topic is dose and safety. Meinke made it clear that effectiveness and safety must be considered together – and that for clinical applications, the demanding path via approval and medical device regulation is unavoidable. Her most important demand at the end was almost cultural: The reluctance to use UV must disappear. Without acceptance, there is no application.

What Needs to Happen Next?

At the end, Michael Kneissl asked the panel about the “next wall” that has to fall so that Deep-UV innovation really arrives in practice. A clear roadmap can be derived from the answers:

• Acceptance & Communication: It is not enough that Far-UVC can be used safely – it must also be understood as safe.
  • Manufacturing & Materials: UV-compatible nanophotonics needs better materials and processes, lower losses and reproducible platforms to reliably bring UV light to the application site.
  • Teamwork between Disciplines: Progress in Deep-UV lasers only occurs when materials science, device physics and engineering work closely together.

Deep UV is therefore not just “a new light”. It is a new toolbox – for germ control without chemicals, for high-precision measurements and for quantum chips. And as is so often the case with real technological leaps, physics provides the opportunity – but whether it becomes an everyday tool is decided in the translation: in products, standards, approvals – and in the art of making complexity understandable.

Notes & Acknowledgements

The panel was organized by Prof. Michael Kneissl, Chairman of the Board of the Advanced UV for Life association and Head of Institute at the Technical University of Berlin.

The Deep-UV session of the Falling Walls Science Summit was made possible by the kind support of Berthold Leibinger Stiftung GmbH.

Image credits:
Photo credits: © Falling Walls Foundation,
© Advanced UV for Life

Further information on the Falling Walls Science Summit can be found at:
www.falling-walls.com