Four classrooms, one light and surprising results

For decades, light was treated as an obvious background element - something that simply had to shine, ideally cheaply and "bright enough". It is only when you begin examining research from years past and comparing it with what we know today about the brain, circadian rhythms and perception that it becomes clear: lighting is not neutral. It affects behaviour, concentration, arousal levels and, in children, processes that are still forming. Dr. John Ott's experiment from the 1970s was one of the first moments when someone saw this, recorded it and named it. Today, half a century later, the subject has returned - not as a curiosity, but as a genuine reference point for the design of modern interiors and lighting systems.

Four windowless classrooms and one question nobody wanted to ask: can light "calm" children?

Yes - it can. And this is precisely what the experiment conducted in Sarasota in the early 1970s demonstrated. Dr. John Ott took four identical, windowless first-grade classrooms and changed just one element: the type of lighting. In two rooms, standard flickering fluorescent tubes were retained; in the other two, full-spectrum light sources replicating natural daylight were installed. Teachers, curriculum, class sizes and room layouts remained unchanged. The result? Differences in behaviour were immediate and visible to the naked eye. Children in the full-spectrum classrooms settled down, sat still for longer, concentrated more easily and showed a marked reduction in hyperactivity.

Importantly, Ott did not rely solely on subjective observation. The entire experiment was recorded using time-lapse cameras, allowing behavioural patterns to be compared over time. The footage - still circulating online to this day - shows something difficult to ignore: the same environment, the same children, yet a completely different level of disruption. And although the internet tends to reduce this experiment to the catchphrase "change the bulbs and the children will calm down", the reality was considerably more complex. Three elements proved to be critical - working in combination:

full-spectrum light closely resembling natural daylight,
the absence of the flicker characteristic of fluorescent tubes (approximately 100 Hz),
an appropriate level of illuminance, significantly higher than in standard classrooms.

Even then, Ott intuitively identified something that neuroscience confirms today: the child's brain is exceptionally sensitive to the quality of light stimuli, and light acts not only on vision but also on the nervous system and the regulation of arousal.

Why did some children suddenly begin to concentrate while others continued to "bounce off the walls"? The role of flicker and light spectrum

The answer is straightforward, though ignored for many years: not all light is processed by the brain in the same way. Conventional fluorescent tubes emit light that flickers at a frequency imperceptible to conscious awareness, yet still registered by the nervous system. Research demonstrates that such flicker can lead to increased tension, irritability, difficulty concentrating and, in some children, an exacerbation of hyperactivity symptoms. This is not theory. It is a genuine problem that was already being described in the 1970s and has since been confirmed in the context of sensory hypersensitivity and ADHD.

The second element is the light spectrum. Standard artificial light sources emit discontinuous light with distinct "gaps" in the wavelength range. To the eye this appears as white light, but for the brain it represents an impoverished signal. Comparative studies have demonstrated that full-spectrum light improves:

sustained attention span,
reading fluency,
the speed of switching between tasks.

Some analyses report 20-26% better performance on cognitive tests and up to 3-4 additional school attendance days per year - making it clear that this is not a cosmetic difference. It is a systemic effect of the lighting environment.

It is also worth highlighting something that is frequently overlooked: children respond to light more strongly than adults. A 2023 meta-review encompassing 59 studies unambiguously indicated that the colour, timing and quality of light have a greater bearing on cognitive functioning in children than in adults. This explains why the effect in Ott's experiment was so pronounced - and why his observations, despite the criticism they received, were far from coincidental.

Ott was right… but he did not yet know about melanopsin. What do we know today about light, the brain and children's circadian rhythms?

The most remarkable aspect of this story is that Dr. John Ott was unaware of the mechanism that we now regard as central. It was only in the early twenty-first century that ipRGC cells containing melanopsin were discovered - a photopigment responding primarily to light at a wavelength of approximately 480 nm. These cells are responsible for regulating the circadian rhythm, alertness levels, melatonin secretion and the synchronisation of the biological clock. In other words: light does not merely enable vision - it governs physiology.

In children, this system is particularly active. Exposure during the day to spectrally impoverished or flickering light can lead to:

disruption of the sleep cycle,
elevated stress levels,
difficulty in winding down in the evening.

Conversely, light closely resembling natural daylight, delivered at the appropriate time and without flicker, supports healthy biological synchronisation. This is also one of the reasons why the relationship between lighting quality and the risk of myopia is increasingly discussed. Research indicates that children spending time in environments with an illuminance level below 1,000 lux have a higher risk of abnormal eyeball development.

Ott did not know about melanopsin, was unaware of ipRGCs and had no access to today's measurement tools. And yet he intuitively identified an effect that can now be precisely explained. This is precisely why his experiment continues to resurface in discussions - not as a definitive proof, but as a starting point for thinking about light in a systemic way, grounded in biology rather than in technical standards alone.

From the fluorescent nightmare to scientific data: what has research confirmed over the past 20 years?

The short answer is: Ott was not fantasising, but some of his observations required refinement and a separation of observation from hard data. Over the past two decades, science has done exactly what could not be done in the 1970s - it has broken down the effects of light into individual components and tested them under controlled conditions. The result? Instead of a single "magical" conclusion, a coherent picture has emerged of the relationship between lighting and human functioning - particularly in children and young people. Meta-analyses and systematic reviews make it clear that light quality translates into measurable outcomes, not merely subjective impressions.

Studies conducted from the 2000s to the present have repeatedly demonstrated that light resembling natural daylight improves attention, cognitive processing speed and the capacity for concentration, particularly in educational environments. Some analyses report 20-26% better performance on cognitive tests, as well as an increase in school attendance of up to 3-4 days per year. These are figures that are difficult to ignore, because they relate to specific, measurable outcomes - not mood or "feeling better". At the same time, science has corrected elements of the narrative from the 1970s - not every full-spectrum light source performs in the same way, and a change in colour temperature alone does not resolve the problem.

What has been corrected? Primarily the oversimplification that every fluorescent tube is harmful and every alternative is beneficial. Research - including studies conducted in the late 1970s and 1980s - demonstrated that the type of light source alone does not determine the outcome. What matters are the technical parameters: flux stability, spectral distribution and illuminance level. Canada's National Research Council identified some years ago that dramatic behavioural effects do not arise solely from the type of lamp, but from the entire lighting environment. This is important, because it shifts the conversation away from "nicer vs. less nice" and towards lighting design as a tool for influencing human functioning.

Why colour temperature alone is not enough: three light parameters that truly make a difference

If someone has ever told you that selecting the "right colour" of light is sufficient and the matter is settled - that is only a partial truth. Colour temperature is a parameter that is easy to describe and market, but it does not capture the full picture. Contemporary research makes it clear that the influence of light on the brain, attention and circadian rhythm is determined by the combination of three elements, not a single slider in a specification sheet.

The first element is the light spectrum - the actual distribution of wavelengths. Two light sources with the same colour temperature can affect the nervous system in entirely different ways if one has a continuous spectrum and the other a "fragmented" one. This is precisely why light can appear similar yet be received in a completely different way at the biological level. The second element is flicker - frequently overlooked because it is invisible to the naked eye. Yet research confirms that flicker at 100 Hz and above can increase fatigue, irritability and the burden on the nervous system, particularly in children and those with sensory sensitivity. The third element is the quantity of light - illuminance measured in lux. Environments lit to below 1,000 lux are increasingly associated with concentration difficulties and, over the longer term, with the development of myopia.

Only when all three parameters work in combination can we speak of light that genuinely supports functioning. Without any one of them, the whole ceases to be coherent. This is why simplified comparisons such as "warm vs. cool light" are now insufficient. Contemporary knowledge has shifted the emphasis from aesthetics to physiology and neurobiology - and that is an entirely different level of conversation about lighting.

If Dr. John Ott had today's technology: what would his experiment look like in 2026?

It would most likely look completely different - not because his observations were incorrect, but because today we have tools that nobody in the 1970s could have imagined. Had Ott been conducting his research now, he would not have needed to rely solely on time-lapse cameras and behavioural observation. He would have had access to precise spectral measurements, flicker index readings, melanopic indicators and dynamic lighting control systems. This changes everything.

The contemporary approach to lighting assumes that light is not fixed throughout the day. Natural light changes dynamically - it energises in the morning, supports alertness at midday and gradually prepares the body for rest as the afternoon progresses. Today's systems can replicate this through dynamic control of intensity and spectrum, without flicker and with maintained high flux stability. This is precisely the direction that Ott anticipated when speaking of "light resembling the natural", even though he did not yet have the language to describe it precisely.

The difference also lies in scale and reproducibility. What was an experiment in the 1970s can today be implemented systematically, with repeatable parameters and full quality control. Flicker-free operation has ceased to be an aspiration and has become an achievable standard. Light has ceased to be merely a source of brightness and has begun to serve as a tool for regulating the biological environment. When you look at it from this perspective, Ott's experiment is not a relic of the past. It is, rather, the first chapter of a story that we are only now in a position to complete.

The same question, better tools - how does contemporary technology respond to Ott's problem? Discover the Polight.ME product range

This is precisely where the story of Dr. John Ott meets the technology available to you today. Polight.ME was created in direct response to the problem that Ott identified half a century ago - that light in interior spaces is too often designed with technical standards in mind rather than biological ones. Rather than focusing solely on colour temperature or fixture wattage, Polight.ME systems replicate the quality of natural daylight, encompassing full-spectrum output, flux stability and flicker-free operation. This is an approach that does not merely "simulate the sun" visually, but works with the same mechanism to which the human brain responds - particularly in spaces without windows or with limited access to natural daylight.

Rather than a single universal solution, a range of lighting series is available, each designed for specific use scenarios. Models delivering a zenithal light effect, uniform wide-angle panels and linear accent solutions all make it possible to build a genuine lighting environment rather than simply adding more light to a space. What is essential is that the light remains stable, flicker-free and predictable for the nervous system - which has real significance wherever concentration, visual comfort and extended time spent in one place matter. This is precisely the element that was missing in Ott's time: technology that allows light to be controlled with precision and intention.

When you examine contemporary research and set it alongside what the experiment of the 1970s revealed, the conclusion is straightforward: the problem has not disappeared - only the tools have changed. Polight.ME uses precisely those tools - advanced optics, state-of-the-art LED sources and solutions designed on the basis of the physiology of vision - to create light that does not distract, does not cause fatigue and does not destabilise the circadian rhythm. This is not a return to an old idea. It is its contemporary, refined version - grounded in data, not assumption.

Four classrooms, one light and surprising results – The Story of Dr. John Ott's lighting experiment