Summarize
- Circadian rhythms are regulated by the body's biological clock in the hypothalamus
- Light has a major impact on circadian rhythms and hormone production
- The colour temperature of LED lights can affect sleep and mood
- Blue light can interfere with melatonin production and sleep rhythms
- Adjusting the colour temperature in appliances can improve well-being
What is circadian rhythm and how light affects it
Circadian rhythms are internal biological processes that regulate sleep-wake cycles, hormone production and other body functions. These rhythms are controlled by the body’s “biological clock”, located in the hypothalamus of the brain. The biological clock is responsible for regulating the timing of various physiological processes, such as hormone release and sleep-wake cycles. One of the most important cues that regulate the biological clock is light.
The human eye has specialised cells called photoreceptors. They detect light and send signals to the brain, which in turn adjusts the body’s internal clock accordingly. Light exposure during the day helps keep the biological clock in sync with the external environment, while darkness at night helps the body rest. Exposure to light during the day and night affects our circadian rhythms differently. Therefore, the type of light we are exposed to and the timing of our exposure are crucial factors in maintaining a healthy circadian rhythm. In this article, we will take a closer look at the effects of LED lights on our circadian rhythm.
As we at LedStore are interested in the effects of light and lighting on human well-being, I went through some online articles and put together this blog post. I hope you will gain new perspectives on the possibilities and uses that LED lights can have. I am not claiming that lighting alone has curative or disease-causing effects, we are not health care professionals and LedStore as a company does not provide medical lighting.
LED lights and their colour temperature
LEDs are commonly used in a wide range of applications, from home and office lighting to street lights and car headlights. One of the unique features of LED lights is their ability to produce light in different colours or colour temperatures. Colour temperature is measured in Kelvin (K) and refers to the visual appearance of a constant light, whether it is warm or cool.
In general, lights with a low colour temperature (2700-3000K) are considered warm and give a yellow or orange hue, while lights with a high colour temperature (5000-6500K) are considered cool and give a bluish hue. Generally speaking, 4000K Kelvin is considered a neutral shade of light, with no blue or orange tint.
As LED lights can emit light at different colour temperatures, they can be used in different environments and for different purposes. For example, warm LED lights are often used in residential environments to create a welcoming and inviting atmosphere, while cool LED lights are more commonly used in commercial and industrial environments to promote concentration and activity.
The science of colour temperature, how colour temperature is measured (in Kelvin)
The science of colour temperature is a way of measuring the visual appearance of light and how it appears to the human eye. Colour temperature is measured in Kelvin (K) and is based on the principle that the emitter of a black body, a theoretical object that absorbs all the light that hits it, emits light in different colours depending on its temperature. The lower the temperature, the warmer the light, and the higher the temperature, the cooler the light. For example, the colour temperature of a candle flame is around 1800 K and looks very warm and yellow, while the colour temperature of daylight at midday can be around 6500 K, or even more depending on where you are on the planet, and looks cool and white.
It is important to note that colour temperature does not measure the power of light in terms of brightness or intensity, but rather the appearance of light. The colour temperature is the temperature of the emitter of an idealised “blackbody” that emits light of that colour. Thus, a light source with a colour temperature of 2700 K emits light that looks similar to the colour of an object at 2700 K (2 426.85 Celsius), but this does not mean that the light source or object is at that temperature.
Different colour temperatures and their effects on our circadian rhythm
The colour temperature of light can significantly affect our circadian rhythms, which are internal biological processes that regulate our sleep and wake cycles and other bodily functions. In general, cool colour temperatures (5000-6500K) are associated with daytime. Shorter wavelengths of light dominate and have been shown to have a stimulating effect on the body, improving concentration. On the other hand, warmer colour temperatures (2700-3000K), i.e. the dominance of longer wavelengths, are associated with evening and night time and have been found to have a calming effect on the body, promoting relaxation and sleep.
Different colour temperatures can affect mood, with cool light being associated with alertness and warm light with comfort and relaxation. Of course, people are individuals, but there is evidence that the right colour temperature for different times of day and activities could contribute to our well-being and overall health.
The totality of white light is therefore made up of many wavelengths, which together form white visible light. The image below illustrates the effects of light wavelengths on human alertness, from the study “Alerting or Somnogenic Light: Pick Your Color” (link to the study at the end of the article). In the picture, a wavelength of just over 500 nm acts as a so-called. a water divider, with wavelengths of light on the left side having an activating effect and wavelengths on the right side having a calming effect. In nature, different wavelengths of light dominate throughout the day.
Studies on the effects of different colour temperatures of LED lights on our sleep rhythm, mood and general well-being
One study, “Effects of light on human circadian rhythms, sleep and mood” (link at the end), found that exposure to cool, blue-enriched light at night increased the risk of sleep disturbances such as insomnia.
Research also suggests that exposure to different colour temperatures of light can affect our mood and general well-being. The study “Effects of new light sources on task switching and mental rotation performance” (link at the end) found that participants exposed to cool, blue-enriched light reported feeling more alert and focused, while those exposed to warm, yellow-enriched light reported feeling more calm and relaxed.
A 2017 study published in The Journal of Clinical Endocrinology & Metabolism, “Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness” (link at the end), found that exposure to blue-enriched white light in the evening led to a decrease in melatonin production and a delay in the sleep-wake cycle in healthy adults. This suggests that exposure to light enriched with blue wavelengths at night could have a negative impact on sleep and other circadian rhythms.
Taken together, these studies and reports suggest that the colour temperature of light can have a significant impact on our sleep patterns, mood and general well-being.
Personally, I take this advice to heart: don’t use an eReader or mobile phone before bed. Of course, today’s devices have blue light filters. And when I look at the screen, I like the rest of the room to have a nice warm tone.
Let’s take a closer look at this eReader survey
The study involved 12 healthy adults with no sleep problems. Participants were randomly divided into two groups: one group read from an eReader four hours before bedtime, while the other group read from a printed book four hours before bedtime. Participants’ sleep rhythms, melatonin levels and alertness the following morning were monitored using polysomnography, actigraphy and subjective reports.
The study found that reading an eReader four hours before bedtime significantly reduced melatonin release. Participants who read from an eReader had significantly delayed sleep onset and reduced sleep efficiency compared to those who read from a printed book. In addition, participants who read from the eReader reported being less alert the next morning.
The authors of the study suggest that the negative effects of reading an eReader before bedtime may be due to the blue light emitted by the device, which can block the release of melatonin and disrupt circadian rhythms. The study suggests that people who want to read before bed should consider using a printed book or an electronic reading device with a blue light filter, or using a dim red light instead, to avoid the potential negative effects of blue light on sleep.
How can blue light in particular disrupt circadian rhythms?
Blue light, with a colour temperature of around 5000-6500 K, is particularly disruptive to our circadian rhythm because it is the most powerful wavelength that blocks the production of melatonin, the hormone that regulates the sleep-wake cycle. Therefore, exposure to blue light at night can make it difficult to fall asleep and lead to insomnia.
Studies suggest that exposure to blue light at night can inhibit melatonin production by up to 22%. This can cause a range of problems, including difficulty falling asleep, insomnia and daytime fatigue.
The problem is that many of the electronic devices we use every day, such as smartphones, tablets and laptops, emit a lot of blue light. It is a natural shade during the day, but it is a good idea to limit exposure to blue light in the evening and at night and to use blue light filters or applications that reduce the amount of blue light emitted by devices.
Tips for adjusting the colour temperature in different devices
Here are some tips for adjusting the colour temperature on different devices:
- On a computer: most operating systems have a built-in feature to adjust the colour temperature. In Windows, you can access it by going to Settings > Display > Night light. On a Mac, you can go to System Preferences > Displays > Night Shift.
- On your smartphone: many smartphones have a built-in feature to adjust the colour temperature. On iPhone, you can access it by going to Settings > Display and brightness > Night Shift. On an Android device, you can go to Settings > Display > Night mode or Blue light filter.
- On TV: many modern TVs have a feature to adjust the colour temperature. You can usually access it from the TV settings menu, or by using the remote control to go to the picture settings or display settings menu.
- On your monitor: some monitors have a built-in feature for adjusting the colour temperature. You can usually access it via the monitor’s on-screen menu or by using the buttons on the monitor itself.
- Software: You can install some software on your computer, such as f.lux and redshift, to adjust the monitor’s colour temperature.
In general, it’s worth trying different colour temperature settings to see which is most comfortable for your eyes. And at night or in low-light environments, a warmer colour temperature is recommended.
Further reading and online sources
“The impact of light from computer monitors on melatonin levels in college students”, published in 2011, from the National Library of Medicine “Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness”, year of publication 2015, retrieved from National Library of Medicine “Effects of light on human circadian rhythms, sleep and mood”, year of publication 2019, retrieved from National Library of Medicine ” Effects of new light sources on task switching and mental rotation performance”, v. 2014, Journal of Environmental Psychology, retrieved from www.sciencedirect.com
“Alerting or Somnogenic Light: Pick Your Color”, published in 2016, from PLOS biology,
Other LedStore articles on led lights and health
- Can Led lights cause cancer?
- Led lights reduce eye strain
- Do led lights help with depression
- Use of LED lights in the treatment of seasonal affective disorder (SAD)
- Led lights improve sleep
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