Does the castle façade shine brighter than a billboard? Scientists from BUT have developed a more accurate device for measuring light pollution.

“Light pollution is slowly killing us and nature. Yet it’s hardly being addressed, because we lack data and standards,” warns lighting technology expert Petr Baxant from the Faculty of Electrical Engineering and Communication at Brno University of Technology (FEEC BUT). Global research on light smog is still in its infancy. That is why experts from BUT have spent the last three years developing a new and more accurate technology for measuring its intensity and its effects on living organisms. The ALANIS system makes it possible to set new light pollution standards and precisely identify who or what contributes to it the most in a given city.

Do people realize how light smog affects them?
Not at all. Many think it’s only a problem for astronomers who can’t see the stars. Some might notice that light kills insects, but the issue is much broader—the entire biological world, from insects to humans, is confused by artificial light signals. We are interfering with signalling pathways that have existed for millennia, such as circadian and circalunar rhythms.

Light smog disrupts the biological clocks of all living creatures. Evidence includes disrupted hormonal cycles in women and a related rise in depression. If you disrupt sex hormones, you affect the whole organism—immune, digestive, regenerative, and metabolic processes all change. Of course, light is not the only factor; lifestyle also plays a role.

So people still don’t really understand the problem of light pollution.
The problem is that its impact on our bodies doesn’t appear suddenly—like sudden chest pain would. It builds up cumulatively, and it will have to be addressed cumulatively as well. The biggest disruption came with LEDs—until then, lighting was used relatively sensibly because it wasn’t cheap. Sodium lamps used earlier emitted light in a spectrum to which nature has a kind of “light blindness.” We can see it, but it doesn’t wake us up.

LEDs pulled us out of circadian darkness. They are energy-efficient and cheaper, which reduces CO₂ emissions, but they produce a different “toxin” — blue light, which gradually harms us. They also lead to overproduction of light. While they offer more lumens per watt, they are designed for daytime vision. This triggers the pupillary reflex, which closes the pupil and reduces light sensitivity. Less light then enters the eye. Simply put: thanks to LEDs we see worse at night and they disrupt our circadian rhythms.

You have now developed a new method to measure light smog more accurately?
Until now, methods only stated the obvious—“we are shining too much.” Brightness of the night sky was measured using a Sky Quality Meter (SQM). But that’s like making a whole city “breathe” into a tube to see if anyone has been drinking—you get a number, but you don’t know who did it. The Ministry of the Environment therefore issued a call for solutions, and BUT responded with the ALANIS – ALAN Information System project.

In addition to evaluation software, we also developed a device called the ALANISATOR. It measures light in both the visible and invisible ranges that affect melatonin production and thus the hormonal system. It also measures the natural level of light—how much there would be if humans didn’t produce any. We call this “light silence”—a reference level experienced by animals and plants without human interference. Human-produced light is measured as an addition to this baseline. The result is an ALANIS score, similar to decibels for noise.

How can “light silence” even be determined today?
Unlike noise, light has no threshold of audibility. So we use a reference—how much light would occur naturally. We based this on moonlight and used a statistical method to evaluate moonlight levels in the Czech environment. The device can identify specific light sources—the panorama, individual lamps, large advertising panels, or illuminated façades. The contribution of each light source is then added to the overall total of light smog.

So ALANIS is both hardware and software. What is it technically based on?
There is a camera with a panoramic module that captures the scene. It includes optics and special filters. In a single measurement, it takes about 80 photographs which are then processed by the software. The user gets light maps similar to Google Street View, enriched with brightness maps and ALANIS scores.

So the project is mainly intended for city administrations?
It can be used by municipal governments, environmental departments, or companies managing public lighting. Potentially also by private entities or architects. Everyone should be interested in lighting reasonably and following a standard—but such a standard still has to be created. So far, we have not defined the threshold at which nighttime light becomes harmful. That is a question for natural scientists.

Our methodology should provide them with a very precise tool to define these threshold limits. These can then be handed over to the ministry, environmental departments, or building authorities, who can use them as a control tool.

Can we even expect private companies to take the harmfulness of night lighting seriously when even scientists don’t have clear answers yet?
That’s why we must work on this urgently. We already have lots of partial findings, and it’s crucial to start now before it’s too late. Natural scientists still don’t know exactly how much light smog contributes to the Life Planet Index (LPI)—how it interacts with light, climate change, pesticides. We don’t know the proportion of the damage light causes. We know it affects insects, which then affects birds. We know mammals and plants react to light smog. But we don’t yet know the full consequences—how it all connects and what awaits us.

How can a person live healthily in this environment—at least as much as possible?

Avoid unnecessary exposure—don’t seek out night parties or discos. Go to bed regularly, ideally by 10 p.m., and align it with sunset. The ideal would be to be in bed an hour after sunset, though that’s hard in modern life. Wake up at the same time every day, even on weekends. The body needs a steady rhythm—weekends are a social construct, not a biological one.

Don’t create sleep deprivation, and expose yourself to bright light as soon as you wake up. This starts the cortisol and serotonin cycles early, which then get depleted by evening so you feel naturally tired. If you wake at 10 a.m., the cycle hasn’t finished and you’re still alert at midnight. Wake early, dim lights in the evening, wear red glasses or turn on night filters on screens.

If we managed to reduce light smog, what would change?
We would experience a wow effect—for the first time we would see the beautiful starry night sky, which is now almost impossible to see anywhere in Europe—you have to go as far as Chile. It saddens me that ordinary people no longer have the chance to see what the natural night sky looks like.

We would also feel healthier. We would return to a more natural cycle and our inner rhythm would synchronize. We wouldn’t need calendars or watches. Today’s society runs 365 days a year, 24/7. But everything around us has its cycles—nature and our bodies. We have disconnected. In winter we no longer rest to regain strength for spring. We are taught to have everything, everywhere, all the time. Lights are everywhere, shops are always open. We have a huge amount of light, but we don’t know how to manage its quality.

If you could tell the public one thing about light smog, what would it be?
I actually have two: First, try to live more gently and avoid contributing unnecessarily. At Christmas you don’t need to wrap your house in lights, and garden trees don’t need festive illumination. If everyone reduced their lighting even a little, the cumulative effect would be significant.

Second, a message to young investigative students seeking a dynamic and promising career: light pollution is a topic of huge importance and we are just at the beginning. There is plenty of room to make a difference, make a name for yourself, and contribute to a more sustainable future. Just in the Czech Republic, there are more than six thousand municipalities that need experts of this kind. The playing field is ready—you can start the research.