Hong Kong is believed to be the world's worst city for light pollution, with levels in Tsim Sha Tsui 1,200 times brighter than a normal dark sky.
The findings were described as shocking by survey leader Dr Jason Pun Chun-shing, of the Department of Physics at the University of Hong Kong.
He said he could find nowhere else on earth as badly affected.
From the notorious hotspot of Tsim Sha Tsui to the remote Sai Kung countryside, the researchers found excessive brightness of varying degrees that scientists said could damage health and wildlife.
Unlike major cities elsewhere - including London, Frankfurt, Sydney and Shanghai - Hong Kong has no laws to control external lighting.
But Secretary for the Environment Wong Kam-sing said he hoped a government task force on light pollution could come up with proposals for more "regulatory elements" for public discussion in the middle of this year.
He did not say if he meant legislation.
In the world's largest light pollution study, scientists collected more than five million brightness measurements at 18 monitoring stations over the past three years. They used an instrument known as a Sky Quality Meter installed on roofs. The worst reading was at the Space Museum in Tsim Sha Tsui from 8.30pm to 11pm, which was 1,200 times the International Astronomical Union standard.
Brightness started to dip after 11pm when lights gradually went out. Tsim Sha Tsui residents once threatened to take developers to court over excessive lights.
Even at the Astropark stargazing facility near High Island Reservoir - where most would expect a natural dark sky - the brightness was still 20 times the standard. Health specialists say light pollution could disrupt the biological clock and affect brain and hormone function.
Pun said that in some European cities like Madrid and Florence, the readings were normally below 100 times the standard.
He said energy-wasting signboards or spotlights that usually point upwards could generally be blamed in Hong Kong.
He added: "Lighting is supposed to provide safety and security for people's daily life. Lights are for human use and not for the sky. But what we see is that many lights are pointing to the sky."
Conservationists were alarmed by the reading at the Wetland Park in Tin Shui Wai at 130 times the standard.
Hong Kong Entomological Society chairman Yiu Vor said he feared the brightness would affect the breeding of fireflies, including the endemic bent-winged firefly, which relied on light signals to mate.
"They might not be able to notice the signals in a bright environment or they simply release the signal less frequently. This would affect their continuing survival." Yiu said insects that relied on moonlight to navigate could also be affected.
Pun said Hong Kong needed tougher measures to curb light pollution, instead of relying on voluntary technical guidelines.
Sydney requires all private illuminated signs to be scrutinised by the city council.
London also makes such nuisances a statutory offence carrying a fine or even imprisonment.