February 23, 2026, 9:57 am | Read time: 4 minutes
Artificial light shapes large parts of everyday life today–even at times when the body is biologically set for darkness. A study aimed to find out how different light sources could influence these processes. The focus was on the hormone melatonin, whose concentration in the body normally increases in the evening, signaling the body that it’s time to sleep.
What Was Examined in the Study?
For the study published in the journal “Scientific Reports,” researchers analyzed 52 commercially available lamps, including LED lamps, energy-saving lamps, and traditional incandescent bulbs.1 Additionally, modern LED lamps were examined, where the light color can be specifically changed from cool white to warm white. The evaluation was based on precise measurements of the color components contained in the light.
Based on this, the authors used an established biological model to calculate how strongly each type of light is likely to affect the natural evening rise of melatonin. The calculations reflect a typical evening use of residential lighting about 30 to 90 minutes before going to bed and refer to a standardized brightness.
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The Results
The evaluations clearly show: Not all light affects the body the same way in the evening.
Cool White LED Light (approx. 5000 to 5700 Kelvin)
This showed the strongest effect. In the model, the evening rise of melatonin was on average reduced by about 12.1 percent. As a result, the body receives weaker signals to become tired.
Cool White Energy-Saving Lamps
The effect was almost identical to cool white LED light. Here, too, the calculated reduction of the melatonin signal was around 12 percent.
Warm White LED Lamps (approx. 2700 to 3000 Kelvin)
They were significantly less disruptive. With warm white LED lamps, the modeled increase in melatonin was only reduced by 3.6 percent, about a third of the effect of cool white LEDs.
Warm White Energy-Saving Lamps
With a reduction of 2.6 percent, they were in a similar range as warm white LED lamps.
Traditional Incandescent Bulbs
They influenced the evening melatonin rise the least. Here, the calculated reduction was only 1.5 percent.
The difference was particularly pronounced with LED lamps with adjustable light color: When they were switched from cool white (around 5700 Kelvin) to very warm light (about 2100 Kelvin), the calculated melatonin reduction dropped from around 10 percent to about 0.1 percent.
The study also analyzed the effect of so-called blue light filter glasses:
- Clear or only slightly yellow-tinted blue light filter glasses showed almost no change in the natural evening rise of melatonin in the model. They largely let through the light component to which the internal clock system is particularly sensitive.
- Strongly brown-tinted blue light filter glasses block this critical light component much more strongly. In the model, the natural melatonin rise was largely preserved as a result.
What Does the Study Mean?
The study suggests that evening light is not just evening light. Depending on the light color, it affects the body’s natural signal to become tired to varying degrees. Cool white light with a high blue component can significantly weaken this signal, while warm light disrupts the natural transition to sleep much less.
Important for context: All results are based on model-based calculations and not on direct measurements of melatonin concentration in the body. However, the study still allows for a systematic and realistic comparison of common light sources under standardized conditions. The actual effect in everyday life can vary depending on individual light sensitivity, actual brightness, distance to the light source, room design, and duration of use.
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