Great writers are said to be night owls as they find the night more productive than the day even though there are debates over body rhythms and the writing process.

"I often think that the night is more alive and more richly coloured than the day," says Vincent Van Gogh, a Dutch post-impressionist painter, while Mahatma Gandhi, a great Indian political philosopher, says, "In the midst of darkness, light persists."

But today it is nearly impossible to find natural darkness even at night. This is not good, not good at all, said experts.

They stressed the need for raising awareness against the nighttime excessive artificial lighting in Dhaka, considering its dire impacts on the biological clock of the human bodies and lives of other animals including birds, bugs and insects that navigate based on light.

Though light pollution is a new phenomenon in the country, some major cities in the world have started acting against the nighttime excessive lighting as it badly affects the mental and physical health of the humans and the lives of other animals, they said.

Alongside controlling air, noise and other environmental pollution, the authorities concerned should now think about the nighttime light pollution also to protect public health and ecosystem as well as save electricity by limiting excessive outdoor lighting, the experts said.

Most recently, a video has gone viral on the social media that some sparrows took shelter inside a house in Dhaka, being frightened by excessive lightings and sounds generated by fireworks and Fanus (sky lantern) during the 31st night celebrations.

Public health expert Dr MH Chowdhury Lelin said every animal leads its life through a circadian clock, but the light pollution changes the biological clock keeping serious impacts on mental and physical health.

"The excessive lighting causes an overstimulated nervous system, headache, sleeplessness, high blood pressure, high heartbeat, irritable mood and vision power of a man. So, it ultimately hampers the normal activities of a human body and one's mental health," he said.

Dr Lelin, also an environmental activist, said the nighttime excessive lighting hampers the sleeping pattern of the human and most birds and other wildlife which badly affect their normal lives during the day.

Besides, he said, the nighttime artificial lighting severely affected the nocturnal animals that they can't intake foods due to the light pollution. Even the nighttime lighting has an adverse impact on plants. So, the light pollution affects the whole ecosystem.

The excessive indoor lighting despite having enough light during the daytime is also considered light pollution, said Dr Lelin.

Biomedical scientist and educationist Prof Dr Liaquat Ali said the light pollution can elicit melatonin suppression, though the hormone acts as an antioxidant.

"If the melatonin secretion declines, it damages its antioxidant effect, disturbs biological clock and immunity. So, the light pollution may cause different diseases like obesity, diabetes and cancer," he said.

It also has adverse impacts on mental health, creating depression and disturbing sleep pattern, said Dr Liaquat Ali.

Urban expert Prof Dr Nazrul Islam, however, said the light pollution is not still so serious in Dhaka, but it is time to think about it.

"Though lighting isn't so extreme here, the excessive lighting should be controlled during celebrations," he said.

Prof Nazrul Islam, also former chairman of the University Grants Commission, said urban planners now need to consider the light pollution in their future works.

Dr Naadir Junaid, a professor at the Department of Mass Communication and Journalism of Dhaka University, said fireworks during different celebrations, including the New Year one in Sydney, London and other major cities in the world are allowed in particular places for short times. But no time and place are fixed here in Bangladesh to celebrate that. "The fireworks generate both sounds and huge light which create a public nuisance," he said.

About light pollution, Dr Junaid said, "We don't see the night sky due to artificial lighting in Dhaka. Large TV screens on the city's streets and shopping malls are also major sources of extreme lighting, which create pressure on our eyes."

According to the website of the International Dark-Sky Association, scientific evidence suggests that artificial light at night has negative and deadly effects on many creatures, including amphibians, birds, mammals, insects and plants.

For billions of years, all life has relied on Earth's predictable rhythm of day and night. It is encoded in the DNA of all plants and animals. Humans have radically disrupted this cycle by lighting up the night, it said.

Plants and animals depend on Earth's daily cycle of light and dark rhythm to govern life-sustaining behaviours such as reproduction, nourishment, sleep and protection from predators, it added.

Noting that artificial lights have devastating effects on many bird species, it said birds that migrate or hunt at night navigate by moonlight and starlight. Artificial light can cause them to wander off course and toward the dangerous nighttime landscapes of cities. Every year millions of birds die colliding with needlessly illuminated buildings and towers.

Many insects are drawn to light, but artificial lights can create a fatal attraction. Declining insect populations negatively impact all species that rely on insects for food or pollination.

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

Since sea turtles live in the ocean but hatch at night on the beach, the coastal artificial lights can lead baby sea turtles to their demise.

The Association says nearly 30 percent of outdoor lighting in the United States is wasted, costing over $3.3 billion in electricity and pumping out 21 million tons of carbon dioxide and other greenhouse gases into the air every year.

According to media reports, approximately 90,000-230,000 birds are killed in New York City alone every year, from striking building glass.

In the New York State Senate, the Dark Skies Act was placed in this January aiming to prevent the deaths of migratory birds and reduce light pollution. The bill would require the majority of non-essential outdoor lights to be turned off, covered, or switched to motion sensor activation after 11 pm. Or else lights could be set to shine downwards.

To combat the negative effects of light pollution, the Pittsburgh City Council in Pennsylvania of the US passed a new Dark Sky Ordinance in 2021 for all of the city's parks, facilities and streetlights.