The Light That Burns: Night-time Illumination and Melatonin Suppression


night lightsDarkness is good for us; it is an ally that heals us. It is something to be embraced, not feared. From Palaeolithic times, up until very recently, the only major sources of light we would have experienced once the sun went down would have been starlight, moonlight and firelight. Life on this planet has evolved for three and a half billion years with a regular and dependable day-night schedule. Now many of us are subject to electrical lighting long into the night, or over the entire duration, the most likely suspect being street lighting. This is far out of balance from how the sleep/wake cycle of our brain’s evolved. This artificial light pollution has a highly detrimental effect on our circadian rhythms, by repressing our nightly melatonin production, the release of which is triggered by darkness. Many people may not consider light to be a pollutant, or to even have the potential to be damaging as it is much less tangible than other environmental pollutants. But excess light, in the wrong place, at the wrong time should be considered a major pollutant that threatens health and well-being. This is especially important given that is well known that melatonin production declines with age as it is, and it is implicated with an ever increasing number of health impacts beyond simply making us feel sleepy when darkness falls. We spend around a third of our lives asleep, so in the long term, this negative exposure to light and the melatonin suppression that results each and every night can add up and affect our health and quality of life in a significant way.

The health ramifications of disturbed sleep and the direct effects of melatonin suppression should be considered separately, while at the same time being intimately linked. Melatonin is an endogenous neurohormone made in the pineal gland in the brain. It is a very potent antioxidant and free radical scavenger, protecting cells, and has neuroprotective properties. It also affects DNA repair, interacting with DNA helicase enzymes and via its actions on several key genes involved in DNA responsive pathways. It acts as a buffer against DNA damage, cellular mutation and cancer, and lowered levels of the hormone have been linked to several kinds of cancer in a number of different studies. Melatonin suppression has also been linked to chronic stress, impaired immune system function and to a number of different diseases. It plays a role in glucose metabolism, and its suppression has been linked with type-2 diabetes. The negative effects of disturbed sleep and sleep deprivation are serious; having been linked to depression, car and workplace accidents, learning and memory deficits and an increased risk of cardiovascular disease and diabetes, and an overall increase in mortality.

Melatonin has neuroprotective properties and may maintain and augment neurogenesis. Melatonin has been found to increase cell proliferation and survival in the hippocampus of aging mice, and melatonin levels decline with age in both mice and humans. The hormone has also been found to enhance the survival of new neurons, enhance dendritogenesis, increasing dendritic maturation and lead to a greater complexity of the dendritic tree and an increased volume of the granular cell layer in the hippocampus of adult mice. The modulating effect of melatonin in neurogenesis could have important implications regarding cognitive ageing and neuropsychiatric disease via the repair of lost dendrites and synaptic connections, so its suppression and potential dietary supplementation are worthy of consideration as we age. The neurogenic effects of melatonin may well be magnified in the young when brains are still developing, so it is important children aren’t exposed to computers, televisions or smartphones too close to bedtime, as high quality sleep is of major importance to brain growth and development.

The evidence for the importance of enough high quality, deep sleep for health is overwhelming. Adequate sleep can act to reduce stress, reduce risk of many diseases, and improve or maintain cognitive function and memory. Recent research has shown that sleep plays an important role in brain detox, with neurons shrinking while we sleep to allow toxins built up to be removed, and there is also an increase in production of oligodendrocytes, the neurons responsible for producing myelin, which acts to protect the neural circuitry of the brain. Uninterrupted darkness during sleep is vital. High quality sleep is so important that if it is compromised via exposure to light it can, to a large extent, negate the benefits of a good diet and regular exercise.

You may be blaming yourself for poor sleeping habits. Exercise, diet, use of intoxicants and stress (or lack of it) are all important factors contributing to quality of sleep. However the importance of melatonin in the nightly sleep cycle cannot be overstated, even if all other life style factors are positive with regard to sleep, and it only takes a tiny amount of light to have a negative impact.

Light exposure at the right time of day may have beneficial effects. In northern and southern latitudes where day length shortens during the winter months, some people can be prone to depression due to Seasonal Affective Disorder (SAD). Exposure to bright light in the morning seems to result in an antidepressant effect while producing an earlier onset of night-time melatonin production, thus timing of exposure to light is important. The benefits of exposure to sunshine, in the right amount and certain times of day, are well known. Only ten minutes of sunshine on the face per day are required for a beneficial effect.

Life-style activities, such as certain types of meditation and yoga have been found to increase plasma melatonin levels, and exogenous melatonin can be obtained through diet (in food sources such as fruits, nuts and grains) and this appears far superior to taking it in the form of a synthetic supplement. Darkness itself can be used as a spiritual tool, and may be one of the oldest such methods employed by humanity. Long term experience of darkness, over days or a few weeks, leads to major changes in brain chemistry, and can bring about some really quite profound changes in consciousness. Darkness retreats may allow people interested in this method of mind expansion to explore this further.

A simple test to see whether you are being affected by light pollution is to turn your bedroom light off at night and let your eyes adjust with your curtains closed. It should be very dark in your room, with the only light being moonlight or starlight. Any more light than this from any other sources may well be having an influence. In an urban environment with many street lights you may still be able to see quite well, and if so this should be a cause for concern, and your health, on some level, will be being impacted. The impact of light pollution doesn’t just affect us, but extends to all of the wildlife living within the vicinity of human habitation. Light pollution in built up areas is intensified when it is overcast, as the light is reflected back down to the ground. These lights also waste vast quantities of energy being on continuously all night, largely unnecessarily. The International Dark Sky Association has calculated that unnecessary night-time lighting wastes upwards of $41.5 billion in electricity costs each year around the world while being responsible for the release of 12 million tons of carbon dioxide into the atmosphere.

Different light has differing impacts on melatonin production, with the amount of melatonin suppression being linked to both light intensity and spectral frequency. High pressure sodium (HPS) bulbs that emit orange-yellow light are commonly used as street or road lighting are likely to be to be one of the widespread culprits responsible for melatonin suppression. This light also appears to be the least potent with regard to this effect of the ones commonly encountered, although their potential impact should be in no way understated. Exposure to short wavelength light (between 440 and 525 nanometres) exerts the most profound effect on melatonin production and should be avoided when possible once the sun sets. “White” light metal halide and bulbs that emit shorter wavelength light (of around 440-500 nanometres) are commonly used in stadium lighting, among other uses, and are worse, having three times the impact on melatonin suppression than the HPS bulbs. The white light emitted by light-emitting diode (LED) bulbs used in televisions, computers, smartphones and notebooks are worse still, suppressing melatonin five times as much as HPS bulbs. Use of any of these should be avoided two to three hours prior to bedtime to ensure deep and restful sleep. Conversely these white light LED’s are considered the most eco friendly sources of light, so while being energy efficient, they seem to have the most detrimental impact on melatonin production. These white light sources such as metal halide bulbs, compact fluorescent lamps (CFL’s) and LED’s should be used sparingly when the sun goes down. While developing energy efficient lighting is certainly warranted, the needs of sustainability need to be balanced with potential detrimental impacts on melatonin production and biology, with both ourselves and other species in mind.


There are a number of things that can be done to eliminate the negative influence of light at times when it will impact us, both on a personal and much broader level. Working night-time shifts should be avoided over the long term with health in mind, and this has been linked to increased cancer risk via melatonin suppression. Working against our circadian rhythms in this long term fashion is not something our brains evolved to deal with and should be avoided if possible. If working at night is a necessity, blue light filtering glasses or googles that filter light below 530 nanometres, can be used to preserve melatonin production and while having no effect on alertness or work performance.

Adjusting lampposts so their light is not directed towards the horizon would drastically reduce unnecessary light pollution, as would shielding the bulbs, or using movement activated lights. Over lighting or using higher lighting levels than is needed for a task should be avoided, and it is important to constrain illumination to where it is needed and for the time it is required. Lights should be turned off when not in use, which will also conserve energy (and money). Manufacturers should be compelled to put spectral wavelength information on packaging for all bulbs, so consumers are able to make informed decisions on what is best to purchase with melatonin production and health in mind, and health regulation regarding the spectral frequency of public lighting should be enforced.

Avoid using computers, smartphones or tablets right up until bedtime (in this sense a book beats a kindle), as light from these will definitely impact melatonin production, and the same applies to televisions, it would be best to avoid having one in your bedroom altogether. Eliminate all sources of electronic lighting from your room prior to bedtime, no matter how seemingly trivial, as a tiny amount of light can have an impact. If you live in an area where light pollution is a factor, investing in some blackout shades or blinds would be worthwhile. Alternatively one could invest in some eyeshades. In the evening, natural light such as firelight, and particularly candlelight are a lot more soothing to the brain, in that they don’t repress melatonin production anyway near as much as artificial light while stimulating relaxing alpha rhythms in the brain. Avoid turning on lights at night if you need to get up and let your eyes adjust if you can. Low wattage or red lights will make much better nightlights regarding impact on melatonin production, and installing such bulbs to act as a nightlight in your bathroom would be a good idea (red light, like that used in photography dark rooms, has the most negligible impact on melatonin production). If you feel your sleep is being negatively affected at present it would be worth experimenting with these things to see if things improve. Some people also recommend using an alarm clock that wakes you with light as oppose to sound, and some report that these may assist with SAD syndrome during the winter and in aligning one’s circadian rhythms in a much smoother way than an alarm which uses sound.

THC in cannabis has been found to substantially increase melatonin levels by up to 4000%. While this may sound advantageous, over the long term there may be implications to the sleep/wake cycle if marijuana is misused via boosting melatonin levels so significantly, particularly during daylight hours. THC dominant cannabis also represses REM sleep, which is a key part of the deep, refreshing, defragging sleep we all need. If people wish to use cannabis, particularly close to bedtime, it is important to seek out strains that are more cannabidiol (CBD) dominant, as this compound has anti anxiety, sleep assisting properties and it balances out the effects of the THC.

A free online software programme called f.lux has been developed which adapts your computer’s colour display to the time of day or night, automatically depending on the time zone you inhabit. As the white light from computers is the most detrimental to melatonin production, this may be something worth looking into. Another simple and more effective option is amber lens goggles once the sun has gone down, these being highly effective in blocking the short wavelength blue light (below 530 nanometres) which exerts the most profound negative effect.

candle lightA recent project on Kickstarter, the Glowing Plant project, was the first ever crowd-funded synthetic biology application, by San Francisco-based hackerspace BioCurious. Its focus is the development of bioluminescent plants via splicing bioluminescent bacterial genes into plants. One day this has the potential of being used to provide bioluminescent trees as an alternative to street lights in residential neighbourhoods as light sources. This cold biological light is vastly more efficient than electrical light, much of which is lost as heat, and is soothing on the eyes, unlike the latter. Much light from biological sources is green in colour, and low in intensity, which has negligible impact of melatonin production. It would also encourage the wide scale planting of trees, save money and conserve energy, while reducing carbon dioxide emissions while also showing people how genetic engineering has the potential to be a highly benign and beneficial force when used well.

This is an important issue, affecting both ourselves and other species all over the world. Light pollution also obscures our view of the stars and cosmos, and so cuts us off, in a visual sense, from the universe. Rules and regulations need to be applied for artificial light use at night and their spectral emissions, in a similar way to how such rules have been applied to other pollutants. While we already know of some of the health implications following melatonin suppression from light exposure at night-time, much remains unknown about the potential implications, and further research is warranted. While awareness of this problem is slowly growing, there are a number of available solutions to this, acting on both a personal, and community wide level for the benefit of all. For change to come public awareness must grow, and the powers that be must be made aware of the scale of this issue, and the various ways of combating it. Making these changes will save money, energy, enhance sleep and protect the health of ourselves, and of other species. It is only through our experiencing darkness that we can truly shine.



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