Select Page

Last But Not The Least: Light Pollution

Last But Not The Least: Light Pollution

By Rupam Debnath (M.Sc. in Zoology, West Bengal State University)


You can not remember when you last saw a firefly in your area. If you live in a rural area it will be a very regular sight in summer evening except urban areas where it is rare. Less than 100 years ago starry night sky was a very spectacular event. Experiencing the Milky Way in the night sky can not possible today in cities. The reason behind this is Light Pollution. Air, water, and land pollution are very common but light can also be a pollutant and a man-made pollution. Widespread use of artificial light at night is adversely affecting our environment causing adverse consequences to human, wildlife and our climate.


The industrial civilization is also a main factor where it includes building lighting exterior and interior, advertising, commercial properties, offices, factories, street lights and over-illuminated sporting venues. Outdoor lighting is extra illuminated, poorly targeted, and improperly shielded. It is wasteful.


There are four components of light pollution. They are as follows:

  1. Light trespass: When light is focused where it is not needed or intended
  2. Glare: It is the excessive brightness that causes discomfort
  3. Sky glow: The over illuminated night sky over inhabited areas
  4. Light clutter: It is the bright, confusing & excessive groupings of light sources, commonly found in urban areas. The proliferation of light clutter contributes to urban sky glow, trespass and glare.


The circadian rhythm of biological system is disturbed by night illumination. Light pollution can confuse animal navigation, alter competitive interactions, change predator-prey relations, and cause physiological harm. The rhythm of life is orchestrated by the natural diurnal pattern of light and dark. So, disruption to these patterns has adverse impact on the ecological dynamics.

Disruption Of Ecosystem

When artificial light affects organism and ecosystem it is called ecological light pollution. Light may be neutral for individual species but its presence also disturbs ecosystem as well as the reproduction, nourishment, sleep & protection from predators related to many creatures including amphibians, birds, mammals, insects & plants.

Nocturnal animals sleep during the day & are active at night. Light pollution radically alters their night time environment by turning night into day.

According to Researchers in case of nocturnal animals, ‘the introduction of artificial light probably represents the most drastic change that human beings have made to their environment.’ Light pollution poses a serious threat in particular to nocturnal wildlife, having negative impacts on plant and animal physiology.

Effects On Insects

We have seen that insects attract to the artificial lights. It is one of the most well known examples of the effect of light at night on organisms. When insects are attracted to lamps they can be killed by exhaustion or contact with the lamp itself, and they are also vulnerable to predators like bats. Dragonflies perceive horizontally polarized light as a sign of water. For this reason, sources of water are indistinguishable from asphalt roads with polarized light pollution to them. They search for water either to drink or in which to lay eggs, often land on roads or other dark flat reflective surfaces such as car & remain there until they die of dehydration.

Light pollution hampers the mating rituals of fireflies, once they depend on their own light for courtship, resulting in decreased populations. Human light pollution is believed to interrupt firefly flash patterns. Scientists have observed that synchronous fireflies get out of synch for a few minutes after a car’s headlights pass. Light from homes, cars, & streetlights may all make it difficult for fireflies to signal each other during mating.

Artificial lights can create a fatal attraction. Declining insect populations negatively impact all species that rely on insects for food or pollination. Some predators exploit this attraction to their advantage, affecting food webs badly.

Effects On Birds

Birds that migrate or hunt at night, navigate by moonlight and starlight. Artificial light can cause them to wander off course and towards the dangerous night time landscape of cities.

Migratory birds depend on cues from properly timed seasonal schedules. Artificial lights can cause them to migrate too early or too late & to miss ideal climate conditions for nesting, foraging & other behaviours.

Effects On Turtles

Sea turtles live in the ocean but hatch at night on the beach. Hatchlings find the sea by detecting the bright horizon over the ocean. Artificial lights mislead them away from the ocean. In Florida, every year millions of hatchlings die in this way.

Effects On Human

Human eyes contain a non-imaging photo sensor which can regulate the human cicardian rhythm. This photo sensor is particularly affected by blue light and when it is exposed to that, the pineal gland stops to secret melatonin. The presence of light at night in human dwellings makes going to sleep more difficult & reduces the overall level of melatonin in the bloodstream. As melatonin is a powerful anti-oxidant, it is hypothesized that this reduction can result in an increased risk of breast and prostate cancer. Instead of this several health effects can be observed like headache, anxiety, fatigue, decrease in sexual function etc.

Effects On Astronomy

Astronomy is very sensitive to light pollution. Sky glow reduces the contrast between stars and galaxies and the sky itself, making it much harder to see fainter objects. This is one factor that has caused newer telescopes to be built in increasingly remote areas.

Effects On Natural Light Cycle

The introduction of artificial light disrupts several natural light cycles that arise from the movements of the Earth, Moon & Sun, as well as from meteorological factors.

Effects On Atmospheric Pollution

A study presented at the American Geophysical Union meeting in San Francisco found that light pollution destroys nitrate radicals. Light pollution prevents the normal night time reduction of atmospheric smog which is produced by fumes emitted from cars and factories.

Effects On Atmospheric Temperature

Dense & unnecessary artificial light sources also emit heat energy to the atmosphere that causes the rising of atmospheric temperature of earth which creates uncomfortable & irritated environment to mankind.


There are several control measures applying which we can reduce and control the light pollution.

  • Adjusting the type of lights used, so that the light waves emitted are those that are less likely to cause severe light pollution problems.
  • In case of streetlights, introducing more smart LED lights instead of low pressure sodium gas bulbs (LPS/SOX), high pressure sodium bulbs (HPS/SON), metal halide, incandescent.
  • It should be remembered that mercury, metal halide and above all first generation of blue-light LED road luminaries are much more polluting than sodium lamps. So, proper selection is needed.
  • Light pollution can be reduced by turning off unneeded outdoor lights, and only lighting stadiums when there are people inside.
  • Unnecessary lights should be moved from houses, factories, streets as soon as possible.
  • Introducing of timers in case of streetlights to reduce the light pollution and energy consumption.
  • Evaluating existing lighting plans, and re-designing some or all of the plans depending on whether existing light is actually needed.
  • Automated or smart lighting should be introduced as pilot projects in the urban areas.
  • Improving lighting fixtures, so that they direct their light more accurately towards where it is needed, and with fewer side effects.
  • Replacement of drop-lens cobra luminaries by flat-lens cobra luminaries as drop-lens cobra luminaries allows light to escape sideways and upwards, where it may cause problems.

Fig: Drop-lens cobra luminaire

Fig: Flat-lens cobra luminaire

‘Power Saver’ Application In Kolkata

‘In a unique initiative to curb energy consumption, the New Town Kolkata Development Authority (NKDA) has taken up a pilot project, which includes switching off one-third of the street lights- on a one kilometer each in New Town- during the night unless a vehicle passes by.’- TOI (Dec 2, 2017)

According to the plan, every third or fourth street light, connected to an automatic sensor, on street will remain switched off after midnight when vehicular traffic is at its lowest & turn on only when a vehicle is detected by the sensor.

Each sensor is placed in a copper loop & embedded underneath the road, at the street’s entry point, on both lanes. When a vehicle enters the street, it disturbs the terrestrial magnetism linked of the copper coil, generating an eddy current. This amplifies switches on the unlit street lights for 5 minutes which is the average time required for a vehicle to cross the 1km stretch. To avoid the challenges like whether a person or any other moving object, including cattle, can trigger these sensors or not, the use of traditional motion sensors, photo-electric sensors & light-based sensors were ruled out.

Fig: Acceptable & unacceptable lighting fixtures (Source: IDA)


The good news is that light pollution, unlike many other forms of pollution, is reversible and each one of us can make a difference! We need to take actions. We can start by minimizing the light from our own home at night. We have to aware others about it and spread the word ‘light pollution’ to our family, friends and tell them to pass it on. Many people either do not know or understand a lot about light pollution and the negative impacts of artificial light at night. If we all come together, we can surely inspire more people to take the necessary steps to protect our natural night sky and surely we can say good bye to light pollution!


c. Power saver: New Town gets smart street lights- Times of India, 2nd Dec. 2017 edition
d. International Dark Sky Association