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A law that promotes stargazing and less confused wildlife begins to take.
Light towards the shorter-wavelength blue end of the spectrum, present in larger amounts in LED lighting, scatters more, creating a brighter halo in the night sky.
It is also this section of the spectrum that most efficiently turns off melatonin production, even through closed eyelids, and attracts moths, bats and birds to spend their time in fruitless circling.
“Those who promote white light always argue that it makes it possible to distinguish colors in the dark,” Mohar said. "But why do you want to distinguish colors in the dark?”
One concession to white light is made on pedestrian crossings, with the lighting industry arguing that older people whose eyes tend to be less good at picking up yellow light find it easier to see hazards.
The organization representing the lighting industry, the Slovenian Lighting Society, is also skeptical about the broader effectiveness of the light pollution laws.
Spokesman Matej Kobav said the authority in charge of policing light pollution simply excuses the inaction of billboard owners and other businesses, citing more serious pollution problems.
"It is very difficult because we are over-occupied with other tasks," confirmed Tatjana Bernik of the Environmental Inspectorate, the agency in charge of enforcing the law. The reason billboards so often go unpunished is technical, she said, "Usually they use LED diodes and it is difficult to find out if they are in compliance or not."Kobav, however, said he accepted the arguments in favor of lighting restrictions, adding that they were a boon for the lighting industry: replacing the street lights in Ljubljana alone would bring in 1 million euros, with upgrades in smaller towns and villages bringing in about 50,000 euros.
He said the zero-degree-rule was too strict, however. Fewer lights would be needed if light were allowed to escape one or two degrees above the horizontal. Such a relaxation would significantly reduce installation and energy costs.
There are signs that Kobav's arguments are gaining ground. The government this month relaxed the laws governing floodlights on football stadiums, allowing them to give off light at five degrees above the horizontal. Kobav hopes further concessions will be offered before full compliance is required in 2016.
Besides, he said: “Restricting light emissions to zero degrees makes it is almost impossible to create a nice view of Ljubljana.”