Cyclists riding around Oahu without lights at night — making them almost invisible to passing cars and pedestrians — are enough of a problem that a bike-advocacy group has launched a campaign to distribute lights to delinquent riders.

“It really is a big safety issue, and it’s a common complaint we hear when we go out in the community from those who don’t bicycle,” said Daniel Alexander, advocacy, planning and communication director for the Kaimuki-based Hawaii Bicycling League.

The nonprofit group is responding in part to data that back those concerns. Several years ago a University of Hawaii-led count near the school’s Manoa campus conducted over two nights found that fewer than half of the cyclists there used a light as required by law. Only 134 of 327 cyclists, representing 41 percent, had the proper light, according to Alexander.

State law requires that cyclists use a front light that’s visible for at least 500 feet ahead of them and a rear reflector when riding at night. HBL recommends riders use a rear light as well, to be even more visible to passing cars.

This past week HBL reported distributing 75 free pairs of lights over three nights at several sites in town and in Kailua. Its members could have provided more if they had more workers on-site, Alexander said.

The group called using lights the biggest thing that someone cycling at night could do to prevent a collision.

Just under half of all fatal bicycle accidents in the United States from 2010-2014 occurred at night, according to a Honolulu Star-Advertiser analysis of federal traffic crash data. Of the 1,509 bicycle riders killed at night during the five-year period, only 63 — representing 4 percent — were using lights.

In Hawaii the federal data show that 13 cyclists were killed in traffic crashes from 2010-2014. Of those, three were killed at night and none were using lights. In September 2014 a 21-year-old woman died after a crash in Kailua. In December 2010 an 18-year-old man was killed while riding a bike in Mili- lani; and in September 2010 a 49-year-old man was killed in Honolulu.

HBL’s campaign to better protect nighttime riders comes ahead of a year in which Oahu likely will see a boost in the number of cyclists getting around town.

The island’s first major bike share program is poised to launch this summer, making 2,000 bikes available for rent in town, 24 hours a day. (Those bikes will feature front and rear lights that activate upon pedaling, Bikeshare Hawaii spokeswoman Jennifer Pang said.)

City transportation officials, meanwhile, aim to link new bike lanes to the King Street Cycle Track to help boost ridership and provide safer route options in a city that’s saturated with cars.

Cyclists represented just 1 percent of all commuters on Oahu in 2014, and it’s hovered around that percentage going back to 2006, the latest U.S. Census numbers show.

“I think next year is when we start connecting the pieces,” city Department of Transportation Services Director Mike Formby said, referring to new bike lanes planned for South and McCully streets. “It should make a difference.”

In its first year, however, the King Street protected lane has drawn heaps of complaints from drivers — including those who say its design doesn’t make cyclists as visible as they should be.

Nonetheless, city officials say the number of cyclists riding on King Street’s busy sidewalks has plummeted since the Cycle Track’s launch, helping to make conditions there safer than before, when more cyclists were weaving around pedestrians and braving the street’s shoulder lanes alongside cars.

Alexander said that HBL would have distributed lights regardless of the new lanes and the increase of bikes to come. It’s part of the 41-year-old group’s ongoing mission to promote bike safety, he said.

This past Monday through Wednesday, after the sun had set, HBL members flagged down all the passing nonilluminated cyclists they could at several intersections: at Kainalu Drive and Kuulei Road in Kailua, at Dole Street and East-West Road in Manoa, and at King and Keeaumoku streets along the King Street Cycle Track. They fastened front and rear lights to the bikes after those cyclists took a brief safety quiz and signed a nonbinding agreement to use the lights.

The group started with 400 pairs of lights, funded through a broad $80,000 grant from the city to conduct bicycle safety workshops and a bike program for seniors, Alexander said.

City transportation officials had aimed to install a protected bike lane at South Street by the end of this year. Amid some push-back from local businesses, they’ve opted to redesign it so that it doesn’t take away any road capacity from cars on South Street, according to Formby. Three major condominium developments going up on the street also prompted the redesign, he said. It’s now slated to be installed in the first quarter of next year at earliest.

The striped lane along McCully Street will be similar to the designated lane that runs along Waialae Avenue in Kaimuki, Formby said. The McCully and South street lanes will each connect to the King Street Cycle Track to help create a grid for cyclists to better maneuver around town, he added.

“Systems don’t really show results until you start connecting the pieces,” Formby said. “You really need to start putting in a net grid.”

HBL is considering distributing more of its lights through December, Alexander said. “Not being visible at night has pretty major consequences for your safety,” he added.