Blue affect the circadian rhythm, purple LED will replace the standard blue LED?
It is accepted that light affects our sleep cycle and health. In modern society, artificial light is ubiquitous and can affect the cycle of day and night as daylight. It is both an exciting opportunity and a potential concern for the solid-state lighting (SSL) industry. In this article, we discuss the non-visual aspects of light and how LED light sources can evolve for the benefit of human health and well-being.
In the early 2000s, based on groundbreaking research on light and sleep, researchers found an unknown cell in our retina: ipRGCs. These cells are light-sensitive. Such cells can receive light and connect directly to the part of our brain that regulates sleep patterns, affecting the circadian rhythm.
The most important of these cells is that they are sensitive to blue light and their peak sensitivity is around 450-480 nm. When stimulated by light, they send out a wake-up signal. This signal can be observed in a variety of physiological responses; for example, it stops our body from releasing melatonin, which is closely linked to our circadian rhythm. The maximum sensitivity to blue light is related to natural light: blue light is more common in the morning, weakened during the day, and not at night; therefore, our body uses it as a reminder of the clock synchronization.
Opportunities and Challenges
On the one hand, it can provide extra light to help those who do not get enough light under natural conditions. For example, a small amount of blue light in the morning can help those who live in areas with insufficient sunshine, or those with less regular circadian cycles, such as adolescents and the elderly. We are particularly sensitive to the morning blue, the first one to two hours after it.
On the other hand, nighttime exposure to light can have unwanted effects. Studies have shown that common indoor lighting conditions (100 lx and above) are sufficient to significantly affect the circadian cycle. This effect lasted for hours after the light shuts down, so it delays sleep. The light from phones and tablets is another issue of concern. With the popularity of LED lighting, this concern has become more serious, especially the use of strong blue LED.
Adjust the spectrum for circadian rhythms
Circadian rhythms are proportional to the amount of blue light. The total amount of blue light is a product of two factors: one is the total amount of light and the other is the relative amount of blue radiation in the spectrum. In order to affect the circadian cycle, you can change the light level and the spectrum.
At present, various measures have been proposed to quantify the amount of blue light, however, this action spectrum has a peak sensitivity at 450-480 nm. Therefore, modifying the spectrum within this range offers the greatest opportunity.
LED technology can be based on the need to form a spectrum, especially to reorganize the spectrum to increase or eliminate blue radiation, but at the same time must maintain the light of other important features. A key aspect is the chromaticity of the light itself, which should be white. If all of the blue radiation is simply removed from the white light source (for example, with a blue-light-blocking filter), the light produced will appear yellow-green, unsuitable for practical use. Therefore, reducing the circadian rhythm of the light source can not be simplified to simply removing blue radiation.
Morning and evening needs
White is characterized by its associated color temperature (CCT). High-temperature light, such as sunlight, contains more short-wavelength radiation, while low-temperature light contains more red radiation (Figure 1). In this way, the circadian rhythm of the light source can be adjusted by adjusting its CCT and intensity, high in the morning and low in the evening. The human visual system naturally adapts to light of different CCTs through a color adaptation process so that a wide range of CCTs is acceptable for general lighting.
figure 1
The figure depicts the chromaticity of various light sources. The black line indicates the black body locus of white light. Removing the blue radiation from the incandescent bulb turns it yellow-green. Although candlelight is technically classified as white light, candlelight has a noticeable yellowish hue.
This method can be very good in the morning and day rhythm, CCT increased to 4000-5000K, and the light intensity to 1000lx above. Various medical studies have demonstrated that blue-light, high-CCT light can help to synchronize sleep time, especially for those who need medical conditions to change the circadian cycle. Therefore, the lighting industry has accepted this concept, and introduced a number of blue-ray radiation products.
On the other hand, it is more challenging to produce a light source that is less irritating at night. In order to reduce the total amount of blue light, the amount of light and the spectrum must be adjusted. The light intensity can be slightly lower, down from a typical 100-300 lx to 30-50 lx, but too dim for home use. More serious challenges arise when it comes to obtaining the spectrum of very little blue radiation, as reducing the color temperature reaches its limit. If the CCT is well below 2700K, which is equivalent to the temperature of an incandescent light bulb, then it is less than perfect. Although technically white, the light is yellow. An example is light from candles; CCT is 2000K, which can be enjoyable in certain situations but looks too yellow for most family activities.
Today, all "sleep-friendly" bulbs use this low color temperature method (color temperature range from 2000-2300K), so light colors are not natural. Due to the quality of this color, manufacturers suggest that this type of lamp be used only for some lighting fixtures, such as bedside lamps. It is noteworthy that the effectiveness of these products so far has not been confirmed by clinical studies.
The same method also applies to the monitor: From smartphone programs such as f.lux to smartphones like Apple Nightshift, the amount of blue light can be reduced by reducing the color temperature of the screen at night. However, the color temperature can only drop to a certain point (about 3500K), and then the screen turns yellow, which looks unacceptable.
Figure 2 shows the amount of blue light emitted by various commercial light sources. From the figure, basically decided by the color temperature. This also reveals a seemingly unavoidable compromise: low blue can only be obtained by a very yellow light color. In fact, this trade-off depends on the basic nature of traditional LED technology: relying on blue-pump LEDs to produce a white spectrum that causes a substantial correlation between the amount of blue radiation and the optical chromaticity.
In the early 2000s, based on groundbreaking research on light and sleep, researchers found an unknown cell in our retina: ipRGCs. These cells are light-sensitive. Such cells can receive light and connect directly to the part of our brain that regulates sleep patterns, affecting the circadian rhythm.
The most important of these cells is that they are sensitive to blue light and their peak sensitivity is around 450-480 nm. When stimulated by light, they send out a wake-up signal. This signal can be observed in a variety of physiological responses; for example, it stops our body from releasing melatonin, which is closely linked to our circadian rhythm. The maximum sensitivity to blue light is related to natural light: blue light is more common in the morning, weakened during the day, and not at night; therefore, our body uses it as a reminder of the clock synchronization.
Opportunities and Challenges
On the one hand, it can provide extra light to help those who do not get enough light under natural conditions. For example, a small amount of blue light in the morning can help those who live in areas with insufficient sunshine, or those with less regular circadian cycles, such as adolescents and the elderly. We are particularly sensitive to the morning blue, the first one to two hours after it.
On the other hand, nighttime exposure to light can have unwanted effects. Studies have shown that common indoor lighting conditions (100 lx and above) are sufficient to significantly affect the circadian cycle. This effect lasted for hours after the light shuts down, so it delays sleep. The light from phones and tablets is another issue of concern. With the popularity of LED lighting, this concern has become more serious, especially the use of strong blue LED.
Adjust the spectrum for circadian rhythms
Circadian rhythms are proportional to the amount of blue light. The total amount of blue light is a product of two factors: one is the total amount of light and the other is the relative amount of blue radiation in the spectrum. In order to affect the circadian cycle, you can change the light level and the spectrum.
At present, various measures have been proposed to quantify the amount of blue light, however, this action spectrum has a peak sensitivity at 450-480 nm. Therefore, modifying the spectrum within this range offers the greatest opportunity.
LED technology can be based on the need to form a spectrum, especially to reorganize the spectrum to increase or eliminate blue radiation, but at the same time must maintain the light of other important features. A key aspect is the chromaticity of the light itself, which should be white. If all of the blue radiation is simply removed from the white light source (for example, with a blue-light-blocking filter), the light produced will appear yellow-green, unsuitable for practical use. Therefore, reducing the circadian rhythm of the light source can not be simplified to simply removing blue radiation.
Morning and evening needs
White is characterized by its associated color temperature (CCT). High-temperature light, such as sunlight, contains more short-wavelength radiation, while low-temperature light contains more red radiation (Figure 1). In this way, the circadian rhythm of the light source can be adjusted by adjusting its CCT and intensity, high in the morning and low in the evening. The human visual system naturally adapts to light of different CCTs through a color adaptation process so that a wide range of CCTs is acceptable for general lighting.
The figure depicts the chromaticity of various light sources. The black line indicates the black body locus of white light. Removing the blue radiation from the incandescent bulb turns it yellow-green. Although candlelight is technically classified as white light, candlelight has a noticeable yellowish hue.
This method can be very good in the morning and day rhythm, CCT increased to 4000-5000K, and the light intensity to 1000lx above. Various medical studies have demonstrated that blue-light, high-CCT light can help to synchronize sleep time, especially for those who need medical conditions to change the circadian cycle. Therefore, the lighting industry has accepted this concept, and introduced a number of blue-ray radiation products.
On the other hand, it is more challenging to produce a light source that is less irritating at night. In order to reduce the total amount of blue light, the amount of light and the spectrum must be adjusted. The light intensity can be slightly lower, down from a typical 100-300 lx to 30-50 lx, but too dim for home use. More serious challenges arise when it comes to obtaining the spectrum of very little blue radiation, as reducing the color temperature reaches its limit. If the CCT is well below 2700K, which is equivalent to the temperature of an incandescent light bulb, then it is less than perfect. Although technically white, the light is yellow. An example is light from candles; CCT is 2000K, which can be enjoyable in certain situations but looks too yellow for most family activities.
Today, all "sleep-friendly" bulbs use this low color temperature method (color temperature range from 2000-2300K), so light colors are not natural. Due to the quality of this color, manufacturers suggest that this type of lamp be used only for some lighting fixtures, such as bedside lamps. It is noteworthy that the effectiveness of these products so far has not been confirmed by clinical studies.
The same method also applies to the monitor: From smartphone programs such as f.lux to smartphones like Apple Nightshift, the amount of blue light can be reduced by reducing the color temperature of the screen at night. However, the color temperature can only drop to a certain point (about 3500K), and then the screen turns yellow, which looks unacceptable.
Figure 2 shows the amount of blue light emitted by various commercial light sources. From the figure, basically decided by the color temperature. This also reveals a seemingly unavoidable compromise: low blue can only be obtained by a very yellow light color. In fact, this trade-off depends on the basic nature of traditional LED technology: relying on blue-pump LEDs to produce a white spectrum that causes a substantial correlation between the amount of blue radiation and the optical chromaticity.
The amount of blue light varies with different light sources. Traditional LEDs reduce blue radiation by lowering the color temperature, which is almost the same amount of natural light at the same temperature, as shown by the orange line. BlueFree technology gets rid of this trade-off and achieves a very low amount of blue light at a comfortable color temperature.
A Blu-ray-free solution
After you identify and understand the root cause of this trade-off, you can actually circumvent it and provide true white light with the least amount of blue light. BlueFree SSL technology developed by Soraa is an example. It relies on a violet LED to replace a standard blue LED, which maintains the incandescent's color temperature by virtually removing any blue radiation from the spectrum by removing energy from a relatively narrow spectral range.
Full violet light based LEDs can significantly improve light quality. Among these full-spectrum products, the violet LED is supplemented with three phosphors (blue, green and red) to produce a very white spectrum of very high color rendering. However, in the BlueFree case, only green and red phosphors are used. By careful selection of these phosphors, very good color rendering can be maintained, despite the absence of blue radiation.
Figure 3 compares the spectrum of various white light sources at the same color temperature of 2700K and illustrates the BlueFree method. The standard LED has a high spectral range in the 440-490 nm range, within which the circadian rhythm sensitivity is greatest. In contrast, the BlueFree spectrum shows very little radiation in this range.
Test theory
To validate the effectiveness of the BlueFree approach, Soraa invited Professor Stanford University Jamie Zeitzer and global experts in the field of sleep medicine to examine their physiological effects. He designed an experiment to measure the "post-illumination pupillary response" (PIPR) of a subject after exposure to light. After temporary exposure to light (pupil dilation from complete to complete contraction), the pupil returns to a residual constriction whose size is controlled by ipRGC cells that control circadian circulation. Higher amounts of blue light show more residual shrinkage, indicating higher circadian rhythms.
Figure 4 shows the pupillary dilation speed of the participants after light stimulation at 35 lx illumination induced by two light sources: standard LED and BlueFree LED, both at a color temperature of 2700K. The two light sources have the same hue, so participants can not visually distinguish them. BlueFree LED produces a more pronounced rate of expansion.
This experiment confirms that BlueFree spectra can significantly reduce circadian rhythms without the use of low color temperature. So BlueFree lamps work seamlessly in home environments, producing white light and good color rendering, with less impact on the sleep cycle.
Due to the presence of cells in our eyes that regulate our circadian rhythms, which are sensitive to blue light, light in home environments, especially blue LED lighting, may disturb our sleep patterns at night and cause long-term health problems. At present, some commercial products try to alleviate this effect by emitting extremely low color temperature light, but yellow tones can be uncomfortable. In contrast, newer technologies can use violet LEDs to produce true white light with almost no blue radiation. Clinical trials by Professor Zeitzer at Stanford University show BlueFree bulbs are much less devastating to our circadian system than standard LED light sources.
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