With rapid urbanisation comes new issues. Few ever give much thought to light pollution, until it shines into their bedroom and keeps them awake at night.

The massive illuminated building facade of Naga 2, the recently opened annex to NagaWorld hotel and casino, is causing a stir with some local residents and raising an issue that is likely to grow as Phnom Penh develops: light pollution.

At dusk thousands of LEDs on the side of the 24-storey Naga 2 building turn on, creating an enormous digital billboard displaying animated vignettes that include fluttering butterflies, rising sky lanterns and the Cambodian flag. While many people have been impressed by the scale of the illuminated building facade – a feature common in cities such as Hong Kong and Dubai but the first of its kind in Cambodia’s capital – not everyone is happy with it.

The owner of an apartment building that faces Naga 2 said he suspects the building’s bright lights, which shine directly into bedrooms of some of the street-facing units, are driving away his tenants.

“In the past my apartment used to be fully rented by foreigners, but recently some tenants started to leave and I don’t know why,” he said. “I feel that some of them left because they were annoyed with light shining in from the nearby building at night.”

A 30-year-old Cambodian woman who lives in another apartment building in the same block said the constantly flickering light keeps her awake at night.

“Why do some buildings use this kind of glass that affects us during our night sleep?” she wondered, adding that the glare is so bright that it lights up her bedroom even after she closes the curtains.

Light pollution can be defined as the adverse impact of the inefficient, unappealing or excessive use of artificial light. This can take many forms, including clutter and urban sky glow. But where city residents most feel its impact is in light trespass – where light shines where it is not intended, wanted or needed – and glare, excessive brightness that causes visual discomfort.

Sat Dara, an engineering professor and a senior officer of the Board of Engineers Cambodia, said the main adverse effect of light pollution on humans is that it prevents people from sleeping, disrupting their circadian rhythms and contributing to sleeping disorders.

In some countries, legislation has been enacted to reduce light pollution, but most governments tend to tiptoe around the issue because of the commercial interests involved. In the US, several states have adopted laws to reduce light pollution, though most regulations are directed at street lamps. The UK has taken a more stringent approach, enacting legislation in 2006 that makes “exterior light emitted from a premises so as to be prejudicial to health or a nuisance” a criminal offence.

“Light pollution regulation is needed in any country that is experiencing rapid urbanisation,” said Dara. “It is uncertain whether or not Cambodia has any regulation in place to control light pollution, but if it doesn’t, it should.”

Met Meas Pheakday, spokesman for Phnom Penh City Hall, confirmed that the capital has never attempted to regulate light emissions from buildings. He said until now, City Hall has not received any complaints concerning excessive or nuisance lights, and therefore has never addressed the issue.

Until now, light pollution has never been an issue in Phnom Penh, where majority of complaints have concerned the absence of street lighting.

Light pollution is likely to become a regular topic of discussion as the capital grows. Other buildings in Phnom Penh that have been labelled by residents as sources of light trespass include the Orkide Villa showroom on Norodom Boulevard, which casts a purple glow on surrounding homes and into the courtyard of Malis restaurant, and the Kid City building on Preah Sihanouk Boulevard.

A woman living in an apartment opposite the Kid City building who declined to give her name said the lights from the brightly-lit building and its digital billboard keep her awake at night.

“I’m happy to see lots of lights along the street, but the lights from some buildings are disturbing my sleep,” she said, adding that she has purchased black-out curtains to stop the light entering her bedroom.

Yet light pollution is not only a problem at night, nor purely a residential issue. The glass and metal used on the facades of skyscrapers going up all around the capital tend to act as mirrors, concentrating intense sunlight on homes and businesses below.

A 40-year-old man who runs a small business on Sotheros Boulevard facing Naga 2 said the tinted glass panes on the hotel and casino complex radiate light and heat on his workplace every afternoon.

“From 3 pm to 5 pm the sunlight reflected off the building badly affects my eyes and body,” he said.