A ray of light in the dark realm: office lighting has weakened the circadian rhythm

In Nile grass rats, which were kept under office-like lighting, the daily fluctuations in activity were weaker than in bright light, which was similar in spectrum to daylight. When the animals turned on a brighter light for an hour in the middle of the day, some rhythm indicators improved. In a separate experiment, scientists found differences in sperm motility. About how the researchers reproduced the working day in the laboratory and what is known about the human reaction to daylight — in the material "Izvestia".

How scientists reproduced office light

Light helps the body's biological clock adjust to the change of day and night. Sleep and wakefulness, the release of certain hormones and metabolism are associated with this internal schedule. For visual work, a person may have enough lighting on the table, whereas the setting of the circadian rhythm is influenced by the light that enters the eyes during the day. Exposure time, intensity, and spectral composition of light are important, the authors of the expert recommendations note.

Researchers from the University of Michigan and the University of California at Berkeley selected Nile grass rats (Arvicanthis niloticus). Unlike laboratory mice and many other rodents, these animals are mostly active during the day. This allows you to compare how their behavior changes during daylight hours under different lighting conditions.

In the first experiment, eight males spent two consecutive weeks in each of the four modes. In one case, the light imitating daylight remained bright for the entire 14 hours of daylight. In another case, it was gradually increased by noon and muted by evening, maintaining the same maximum. Two more modes reproduced dim fluorescent lighting, and in one of them, light close to daylight was turned on for an hour in the middle of the day.

The illumination with constant imitation of daylight was about 5.6 thousand lux. According to the authors, this level is comparable to the light outside on a cloudy day. The office mode gave about 150 lux. We are talking about the parameters of a specific experiment. The researchers measured light at the cell level, and the modes differed in both illumination and spectrum.

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What changed after an hour of bright light

The movement of the animals was recorded continuously. Under constant bright light, the rats moved more during the day, and the difference between daytime and nighttime activity was most pronounced. Daytime activity was lower in dim fluorescent light. At night, the scientists did not find any significant differences in the total volume of traffic between the modes.

Simulating dawn and dusk with the same midday maximum produced about half as much light energy per day as constant bright lighting. This mode was inferior to constant light in terms of the intensity of the rhythm. The authors suggest that the total light received per day is important for the biological clock. The shape of daylight also changed in the experiment, so the contribution of two factors has yet to be clarified.

An hour of bright light in the middle of the day partially increased the daily fluctuations in activity against the background of fluorescent lighting. At the same time, the difference in the ratio of daytime and nighttime activity between the two office modes did not reach the accepted threshold of statistical significance. All eight rats underwent the regimens in the same order, so the authors also allow for the contribution of animal age and other changes during the experiment.

What did the glucose and semen tests show?

Another 20 males participated in the second experiment. Ten of them spent six weeks in constant light close to daylight, while the rest spent six weeks in fluorescent light. The researchers did not find a statistically significant difference between the groups in terms of body weight and average glucose levels. At the same time, the values characteristic of the diabetic state in this model were recorded in four out of ten rats under office lighting and in one out of ten under bright lighting.

Reproductive parameters were measured in five males in each group. The proportion of motile spermatozoa averaged 19% in fluorescent light and 45% in simulated daylight. The proportion of cells capable of progressive movement was also lower. The number of spermatozoa did not differ significantly. The authors measured the properties of cells in the laboratory, but it is too early to judge the ability of animals to reproduce from these data.

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The results of the two experiments answer different questions. An hour of bright light was added in an experiment where movement was observed. There was no such regime in the six-week analysis experience. It remains to be seen whether midday lighting can affect glucose or sperm motility.

What is known about lighting and metabolism in humans

In January 2026, the journal Cell Metabolism published a study involving 13 people with type 2 diabetes. The volunteers randomly spent 4.5 days in two conditions. During working hours, the room was illuminated either through windows or by electric lights. The sensors showed that in daylight, the participants' glucose levels remained within the normal range set in the study for longer.

When working with people, it was about short-term glucose control in patients with an already established diagnosis. To assess the effects on office staff, longer observations are needed in a normal work environment.

One of the questions for such studies is whether health indicators will change if employees receive more daylight with the same work schedule and comparable physical activity. Separately, it is necessary to find out whether it matters whether the light comes through the window or a person spends part of the day outside.