The City of Montreal is opting to replace 132,000 streetlights with 3000K LED lights, which give off a warmer hue than the ones it originally planned to install, in response to concerns about health hazards and light pollution.

After the city first announced its plans to replace the existing high-pressure sodium lights with more energy-efficient LED lighting, some people expressed fears the 4000K lights it intended to use would be too disruptive.

The 4000K lights emit a blue-rich light, closer to simulating daylight than the 3000K LED lights do.

In guidelines adopted by the American Medical Association (AMA) in June 2016, the AMA cautioned against the use of LED lights which "emit a large amount of blue light that appears white to the naked eye and create worse nighttime glare than conventional lighting."

"Discomfort and disability from intense, blue-rich LED lighting can decrease visual acuity and safety, resulting in concerns and creating a road hazard," the AMA said.

Beyond driving hazards, it noted that blue-rich LED night-time lighting suppresses melatonin and "is associated with reduced sleep times, dissatisfaction with sleep quality, excessive sleepiness, impaired daytime functioning and obesity."

$100M conversion

"After taking note of all the information, notably on the issues of security, light, atmosphere and public health, we chose to move forward with a less intense luminosity," Montreal Mayor Denis Coderre said in a statement.

Coderre said the city is trying to strike a balance between health concerns and the need to make sure public areas are adequately lit, for safety.

Denis Coderre

Montreal Mayor Denis Coderre says he wants streetlighting to be adequate to ensure people feel safe at crossroads, parks and other public spaces. (CBC)

"We want to make sure that in crossroads, in parks, that people will have the capacity to feel secure," he said.

It will take five years and cost $100 million for the city to replace all the light bulbs. 

Of that money, $28 million will be spent on a smart lighting system that the city says will allow it to respond more efficiently to broken or malfunctioning lights, as well as monitor energy consumption.

The city expects to save 35 per cent on energy costs and 55 per cent on maintenance, once the streetlight conversion is completed.

Cities respond to medical findings

Adverse effects of LED lights have been identified in recent years as several U.S. and Canadian cities have moved to replace older streetlights with more energy efficient ones.

The culprit, according to the AMA, is the amount of blue light emitted by LED lights with a higher Kelvin (K) value.

Lights in the 2700K to 2800K range are considered "warmer" lights, in the colour temperature range of common incandescent light bulbs. Lights that simulate bright daylight are in the 5000K to 6500K range.

Cities have responded in different ways to complaints about the adverse effects of the higher K-value lights.

New York City switched to lower K-value LED lights after a growing number of complaints.

In Sherbrooke, the city's proximity to the Mont Mégantic astronomical observatory led to concerns about light pollution, and it opted for much dimmer 1800K LED lights.

Toronto is sticking to 4000K lights over main arteries, and Seattle, Washington has reserved its right to use extremely bright 4100K lights.