A)Melanopsin receptors in the retina are specific for 460-485nm wavelength light and signal the suprachiasmatic nucleus which controls the circadian rhythm.
B)Visual receptors in the retina have different sensitivities than melanopsin receptors.
The impact of light on our sleep cycle and health is a major medical discovery of the last two decades. Research shows there are special receptors (blue-sensitive receptors/ melanopsin receptor) in our retinas, which are sensitive to light, but rather than causing a visual stimulus (like the well-known rods and cones), they connect directly to the part of our brains which is regulates our sleep patterns and health circadian cycle.
These receptors, importantly, are most sensitive to blue light- their peak sensitivity is at wavelength of about 460-485mm. When excited with light, they send a “wake-up” signal. This signal is observed in various physiological responses; for instance, it prevents our body from releasing the hormone melatonin, which strongly correlates to our circadian cycle.
This blue wavelength sensitivity cannot be explained by the spectral sensitivity of the rods and cones in our eyes. For over hundred years, we have known that day time color vision relies on cone receptors that provide color information to the brain. While the cones can respond to all colors in the visual spectrum. They are most sensitive to green light. Nighttime vision is dependent on rod receptors that can see even when light levels are very low. The pathways that carry visual images from the rods and cones to the brain have been well mapped and understood. But neither rods nor cones are highly sensitive to the blue-wavelengths that reset circadian rhythms and suppress melatonin.
The important discovery, Which explained the blue light sensitivity was the identification of special types of photo receptor cells in the retina containing melanopsin, a photo pigment with peak sensitivity to 460nm blue light. The melanopsin receptors are 25times more responsive to light at this blue wavelength than to full spectrum white light. When activated by blue light, the melanopsin receptors send information via a special neuronal pathways directly to the suprachiasmatic nucleus (SCN) in the brain. These melonopsion pathways are quite separate from those that carry visual images to the brain. The SCN is the body’s “master circadian biological clock”. It thus became clear that, just like our ears have the two functions of hearing and balance. Our eyes have the two functions of seeing visual images and regulating the brain’s master circadian clock.
Ficture2: In contrast with the normal LED light and
Vestralux Nightlite(Blue-low) light.
Natural night after sunset is associated with the absence or very low levels of bioactive blue light content. The lack of blue light provides a night signal to the master clock and triggers a chain reaction that activates hormonal and other pathways critical to maintaining health and avoiding depression, diabetes, obesity, cardiovascular disease, and breast and prostate cancer. Around 9 PM melatonin secretion starts to climb and this a critical signal that circadian night has begun. Body temperature is lowered, and bowel movements are suppressed.
Melatonin secretion peaks around 2 AM, then starts to drop and terminates by 7 AM, signaling the start of a new day.Just as the presence of bioactive blue light is critical to maintaining circadian day functions, the absence of bioactive blue is critical to maintaining optimal circadian night functions.
This maximal sensitivity to blue light makes sense as it is relates to natural sunlight: blue radiation is more prevalent in the morning, diminishes throughout the day, and is absent at night; therefore, our body uses it as a cue to synchronize its internal clock.
Artificial light ,which is ubiquitous in modern societies , can influence the circadian cycle just like sunlight does.
Exposure to light in the evening can have unwanted effects. Research has shown that common indoor lighting conditions are enough to significantly impact the circadian cycle, and thus delay the onset of seep. Display light from phones and tablets is an additional cause for concern. Myriad of electronic devices that emit blue-rich light(smartphones , TVs ,automobiles ,tablets ,e-readers ,etc.) this worry has become even more acute with the spread of LED lighting, which uses blue-pump LEDs whose intense blue radiation is especially impactful.
To make matters worse, exposure to the wrong light at night can lead to depression and mood disorders. Individuals who work rotating shifts feel as though they exist in a state of permanent ”jet lag”. Light at night is contributing to the diabetes epidemic and increases the chance of getting breast or prostate cancer. In the 2007 the World Health Organization’s (WHO) international Agency for Research on cancer identified night shift light exposure and circadian disruption as a probable carcinogen, especially with breast cancer in women. WHO stated that the finding was consistent with “experimental studies show that reducing melatonin levels at light increases the incidence or growth of tumors ” By 2012 sufficient data had accumulated for the American Medical Association(AMA) policy statement to go much further. The AMA confirmed that night time lighting exposure risks include carcinogenic effects related to melatonin suppression, especially breast cancer” they further added that other diseases that are exacerbated by nighttime light ”include obesity, diabetes, depression and mood disorders ,and reproductive problems”.
Every evening, the hormone melatonin activates sleep and other nighttime processes in our bodies. Melatonin is a primary contributor to our health.
Exposure to blue wavelengths of light during evening hours (or pre-sleep hours for shift workers) suppresses the release of melatonin and disrupts sleep (especially restorative sleep) and circadian rhythms.