Why does the sky glow purple?

Anyone driving at night in parts of  Pajaro Valley may occasionally notice an unsettling purple glow illuminating the sky.

This comes from LED lights used by cannabis greenhouses to create longer light cycles young marijuana plants need to grow. 

And while the burgeoning cannabis industry has become a part of the local agriculture industry since voters legalized recreational marijuana in 2016—taking space in farms and greenhouses once occupied by food crops—the result of the red and blue lights adds to existing light pollution, says Lisa Heschong, a fellow of the Illuminating Engineering Society and part of Dark Sky Santa Cruz. 

That can harm wildlife and diminish enjoyment for night sky enthusiasts hoping to catch a glimpse of the stars and planets, she says.

“We are living in, or adjacent to, the Monterey Bay sanctuary,” she says. “We have a plethora of state parks with endangered species such as the steelhead trout that migrate through the San Lorenzo River, and light pollution is interfering with all those ecological systems that are so precious to us.”

And this means that Santa Cruz, once considered a place removed from larger and brighter cities, has lost its luster for astronomy buffs. 

“People have spoken about coming to Santa Cruz to be able to see the night sky and get away from the glare of the Bay Area, but that is going away,” Heschong says. “We’re losing our night sky in Santa Cruz also.”

While state regulations address energy use in buildings, agricultural buildings are excluded, because it was assumed that light was not a major component of those operations, says Santa Cruz County Cannabis Licensing Manager Sam LoForti.

But Santa Cruz County residents, at least the ones who live farther away from Monterey County, will likely not have to contend with the glowing purple of nighttime greenhouses. That’s because the county has an ordinance governing outdoor lighting and its effects on neighbors.

“We have a requirement that you can’t have pollution,” LoForti says. “You have to have full blackout curtains on your greenhouses.”

In Monterey County, ordinances prohibit neighbors from illuminating nearby properties and require that lighting be unobtrusive and that long-range visibility is reduced. But the county has no such ordinance regarding nurseries, meaning that the greenhouse in question—Wave Rider Cannabis Co.—is not breaking any rules. 

The business did not return requests for comment.

Despite a growing number of businesses entering the cannabis market, state lawmakers have left the issue of light pollution virtually untouched, Heschong says. 

But the new and emerging problem needs attention. Heschong says.

“It’s very unnatural, it’s not good for the neighbors, it’s not good for the plants and animals that are nocturnal,” she says.