Artificial Light at Night is a Rapidly Growing Problem with Serious Health & Ecological Implications; Solutions are Relatively Simple: A Public Information Feature

  Blog Contents and Who am I?

"Air, noise and water pollution have been high priority policy issues for decade, but light pollution remains scientifically, culturally and institutionally in the the dark"   ...The Atlantic 2019

Light and dark are concepts deeply embedded in our cultural and genetic heritage.  For a lot of people, it is hard to comprehend that light can have negative consequences.  The past 150 years have witnessed an explosion of artificial lighting (man made illumination) that has seriously disturbed the predictable natural rhythm of day and night.  The evolution of living organisms has been  controlled by the natural cycle of light and dark. Since the introduction of electric light bulbs, anthropogenic light has disrupted this status quo with many adverse consequences, not only for humans but for animals and plants too.

The two main problems with artificial light are the excessive amount of light illumination and its colour spectrum.  Urban centres are the regions where light pollution is the most serious. Urbanisation is a megatrend with a projected 70% of global population living in cities by 2050, and one expects that adverse effects of light pollution will continue to increase. 

(Click on a slide to view it full page image) 

Bright lights from cities are clearly evident when viewed from space.  Some of the city light is scattered back to the Earth by dust and gas molecules in the atmosphere, and gives the sky a diffuse brightness - what we call the skyglow.  Skyglow can make the city sky more than a hundred times brighter than the sky in rural areas far away from man-made lights.  Skyglow is so prevalent that several billion people (80% in the USA and >60% in Europe) cannot see the Milky Way (Click here for some good pictures). Astronomers measure skyglow from levels 1 to 9 on the Bortle scale; watch this 3 minute video to see how stars and the Milky Way are disappearing under the impact of artificial lights. 

It is also a serious threat to nocturnal wildlife. On a cloudy day (when there are more particles in the atmosphere), much more light is scattered back to the Earth and night skies over cities can be more than 20 times brighter than on a cloudless night (more details here). 

 

Other forms of light pollution are known as clutter, trespass and glare. The terms are self explanatory - there are many good articles on these topics and I refer you to 1, 2, 3 and 4.

 

In this publication, I shall look at the science of light pollution with particular emphasis on the effect of recently introduced light sources (compact fluorescent lights CFL, and light emitting diodes LED) on chrono-biology.  The next slide lists some of the impacts of light pollution:  

Light Pollution and Human Health:  For millions of years, human physiology has been governed by our internal biological clock or circadian rhythm (CR).  CR follows a rough 24-hour cycle - it not only controls your sleep/wake pattern but many body functions rise and fall at set times of the day based on your circadian rhythm, see also. For the importance of sleep, I refer you to 1 and 2.

Circadian Rhythm and your sleep/wake pattern may be affected by the amount of ambient light (jet lag is a good example where the time shift after a long plane journey may expose you to a diffrent day/night cycle) and by its spectral properties (intensity distribution with wavelength or colour).  Night shift workers are particularly vulnerable and suffer many serious health problems directly attributable to the unnatural ways that they are exposed to artificial light.  New artificial light bulbs introduced over the past 50 years are economical to run but have a spectral signature that is relatively rich in short wavelengths (blue light).  Exposure at night to blue light of wavelength around 480 nm has been shown to be particularly detrimental to maintaining a natural circardian rhythm.  

 

Understanding Artificial Light (AL) :  Artificial light (man made light) has made dark periods of evenings and nights  accessible for human activities that, otherwise, would have been impossible. Some aspects of artificial lighting are at odds with our evolutionary biology, and there is growing unease about the way we use/abuse AL. Our circadian rhythm evolved with natural light and requires exposure to bright light in the mornings and longer wavelengths of light (yellow-red) during evenings (see slide).  

 

The old style incandescent light bulbs (ILB) emit light by heating a tungsten filament to high temperatures around 3000C.  The light spectrum, as it happened, closely matches  the spectrum of sunlight at dusk.  While overillumination (use of excessive unneeded light outdoors) was a problem, artificial light from ILBs did not cause serious disruption of circadian rhythm. 

 

Around 1950, significant changes happened in the way artificial light is generated.  ILBs were inefficient (~10%) with  90% of the electrical energy wasted as heat.  Far more efficient (~ 50%) compact fluorecscent light (CFL) arrived first, with super efficient (~85-90%) light emitting diodes (LED) have now completely replaced ILBs.  Unfortunately, increased efficiency made light inexpensive and Jevons paradox kicked in.  AL is now used excessively and needlessly with overillumination becoming a serious problem causing skyglow, clutter, glare and tresspass. Human societies now live in contradiction with their biological heritage - they are indoors during the day with less exposure to bright lights, and then they switch on bright lights of the wrong spectral makeup during the evenings and night - exactly opposite to how we evolved.    

The hue of a light source is rated according to its CCT value.  This is explained in the next slide:

The spectral profiles of LED and CFL bulbs are shown in the next two slides:

In the past, sodium discharge lamps were used for outdoor light illumination.  Sodium lamps are being replaced by the much more efficient LEDs.  While the CCT of sodium lamps is around 2200K and they appear yellow, LEDs tend to have a much higher CCT value and there is a lot more blue tinge in their light.

The following slide shows the remarkable difference in the Milan city lights after HPS lamps were replaced by LED lights (as seen from space):

Milan is typical of most big cities.  The slide demonstrates that much of the outdoor lights that are meant to illuminate the roads and infrastructure is sent upwards and therefore wasted.  This is a good example of unplanned, careless and wasteful use of energy that not only adds to costs but also sends large amounts of greenhouse gases into the atmosphere contributing to global warming. 

Artificial light consumes 19% of global electricity production and emits 1.9 gigatonnes of CO2.  The worldwide use of artifical light is increasing by about 6% per year.

Production of Many Hormones is Affected by Light: Several hormones show daily oscillations (circadian rhythm).  Melatonin (controls sleep), cortisol (activity and stress), gonadal hormones progesterone & testosterone (sex), thyroid and growth hormones are known to have circadian rhythm.  Nutrient sensitive hormones like insulin, leptin, ghrelin also oscillate on a circadian basis, and their release is at least partly regulated by light-dark cycles.

In order to emphasize the importance of maintaining a good circadian rhythm by the provision of proper light-dark cycle and correct spectral quality, I shall look at the particular case of melatonin production. Melatonin is called 'the sleep hormone'; its production increases as dark hours set in.  Blue light has been shown to suppress melatotin synthesis:

Melatonin synthesis in the pineal gland requires availability of serotonin that in turn is made from the essential amino acid tryptophan.  Tryptophan is present in high protein foods like egg white, cod, cheese, sunflower seeds etc. and efficient synthesis of serotonin happens in the presence of bright lights.  In fact, there is good evidence that mood seasonality  - seasonal affective disorder (SAD) - is due to low availability of serotonin.   Being in bright sunlight during the day for an hour helps serotonin production which in turn helps in melatonin synthesis.  It seems that for ensuring good sleep, it is also important to spend some wake time in bright sunlight. 

The above discussion establishes that for efficient melatonin production blue light exposure must be minimised after evening sets in. This should ensure proper sleep (lasting 7 to 8 hours) that is essential for maintaining circadian rhythm.  Why sleep is important and how our health is affected by poor quality and/or insufficient sleep has been comprehensively covered by my publications (1, 2) and I refer you to them for details. 

Impact of Light Pollution on Animals and Plants:  Animals and plants belong to the Earth's ecosystem as much as humans do - we all have evolved together over millions of years under the daily rthythm of light and dark. Compared with other environmental features like temperature, atmospheric constituents, climate etc., light and dark cycles have been extremely stable, and biological systems are unlikely to have developed the ability to easily/rapidly adopt to sudden changes in the level of light at night.  

Artificial light at night (ALAN) has possibly disrupted the rhythm of life far more for animals and plants than it has affected humans.  ALAN pervades large geographic areas - for example, the sky glow from cities may be visible from hundreds of kilometres away.   With the exception of more general loss of view of the Milky Way and stars, ALAN only affetcs humans living in cities.  Humans  can also control their exposure to ALAN, but nocturnal animals have no such options available.  Nocturnal animals have used light from the Moon and stars (brightness ~0.1 lux) for activities like migration, searching for food, habitats and mates. Excessive brightness of ALAN can seriously disrupt animal physiology, biological timings, behaviour and welfare - it has the potential to disrupt entire ecosystems. Many animals (fish, insects, turtles) have high sensitivity to blue light; the recent widespread use of LED lighting, that has a high content of short wavelength blue colour, have further accentuated the adverse effects of ALAN.  

Over the past 25 years, scientists have started studying how ALAN affects animals (both terrestrial & aquatic) and plants, but much work remains to be done to properly understand the ecosystem damage due to artificial light. Cities are expected to grow rapidly, exacerbating associated light pollution at night;  the situation requires urgent attention.  

What can be done to control Pollution by Artificial Light at Night (ALAN)?

Unlike other pollutants, ALAN is easily controllable - on a basic level, just switch off the lights and the effects of light pollution could be eliminated on a swift time scale.  However, life does not work that way - for generations, ALAN has delivered many benefits like extended work and recreational hours, and night activity is part of our lifestyle and culture - it is not possible to go back to preindustrial life.  But, there are many ways that we can reduce the harmful effects of ALAN on humans and rest of the ecosystem.  A mixture of good planning, design, education and common sense is required.   

It is important to realise that, until now, very little planning has gone into how we use outdoor lighting - 30 to 60% of energy consumed in lighting is unneeded.  This represents lost resources and also contributes to climate change. Many organisations throughout the world are actively promoting awareness about light pollution at night and working towards reducing the negative biological effects of ALAN - controlling ALAN saves money and it is good for health and the environment too - it is a win-win situation for everybody.  On an individual level, one needs to act to maintain a healthy circadian rhythm for your own health, and also consider ways to minimise the polluting effects of outdoor spaces. 

In order to reduce the polluting effects of artificial light at night, 

we can take some simple common sense steps to start with:

Outdoor Lighting:

1.  Turn off unneccesary lights: Most outdoor lights are switched on at dusk and stay on during the whole night. We do not really need street lights after about 1 am when both the road and pedestrian traffic is extremely low.  Most outdoor lights can be switched off for part of the night with significant cost savings as an additional benefit. 

Various studies have cast doubt on the security and crime reduction aspects of outdoor lighting.  Motion sensitive lights with surveillance cameras situated at appropriate places would be far more effective measures.  

2. Down-shield exterieor lights: Probably one of the most important measure one can  take to reduce skyglow, glare and trespass.  Most outdoor light fixtures in use emit light in all directions - there is no need to shine light upwards or even horizontally.  Properly shielded lights with reflectors can illuminate the desired area only and minimize light pollution by using much less energy and save costs.

3. Use high-efficiency warm white lights:  LED lights are super efficient and convert ~90% of electricity into light.  They are also controllable in the direction and intensity of emitted light.  LEDs do emit more blue light than the alternative high pressure sodium lamps.  By choosing a warm white temperature LED rated at < 2700K, one can increase the proportion of yellow and red wavelengths and reduce the impact of the light on humans and wild life.

4.  Use timers and motion-sensitive lights:  Motion sensitive lights only come on when needed - installing them can reduce  significant amount of light pollution and provide big cost savings without compromising safety and comfort.

5.  Optimise Light Intensity:  Light used should be at the lowest intensity required.  Again, timers can reduce the intensity of light during periods of low use (after midnight for example).  At present, lights that are too intense are used causing unwanted skyglow and glare.

Indoor Lighting:  Indoor lighting is most relevant for human health and with the introduction of economic-to-run LEDs, wasteful use of light has significantly increased.  Measures for reducing the impact of outdoor lighting are also applicable for indoor lighting - switching off lights in unoccupied areas, use of dimmers to reduce excessive intensity etc. - smart technology can be very effective. 

Most importantly one must avoid exposure to short wavelength blue light - for LED lights, the use of blue light blocking goggles at least two hours before bedtime is highly recommended as this ensures sufficient melatonin production for good quality sleep.

At night time, it is important to close the curtains, switch off porch & garden lights to ensure that glare and skyglow are not increased.   

Community Awareness:  The damaging effects of light pollution are not widely appreciated.  It is important to educate ourselves about these and help our neighbours and wider community to understand the issues involved.  In most areas, local authorities are responsible for the planning and installation of outdoor lighting.  Most measures to reduce light pollution save money, and it should not be too difficult to convince civic authorities of the merits of good design that provide optimum illumination levels at times of the night when it is required. 

Thanks for reading.  Please pass the link to this blog to friends, family and neighbours.