The Guardian Climate Desk Locals in a rural area California were recently startled to see dazzlingly bright light shining down from nearby mountains at night, illuminating a swathe of the desert below.

Unbeknown to them, the strange nocturnal illumination was the latest step in a company’s plan to erect thousands of giant mirrors in space to reflect sunlight on to the Earth during night-time.

The nighttime light demonstration, near the town of Lone Pine in the Sierra Nevada region, was conducted by a startup called Reflect Orbital which has an almost sci-fi aim to launch 50,000 satellites into space in the next decade to illuminate parts of the world at night.

“Literally all of life on Earth evolved based on the rhythm of day and night, and there is a ton of data showing that messing with this is not a good idea.”In July, the Federal Communications Commission (FCC) approved Reflect Orbital’s proposal to launch an initial demonstration satellite next year, which will orbit the Earth and, via a 59-foot-diameter mirror, reflect sunlight in 3-mile-wide beams in strengths from moonlight up to the brightness of the sun at noon.

The demonstration in California, undertaken earlier this month, showcased what this would look like on the ground, to the bewilderment of locals, one of whom called the lights “blinding.”Large mobile lights were erected near Mount Whitney, with Reflect Orbital comparing the radiance to that of a full moon.

This provided, the company said, a realistic simulation of one of the benefits of this technology: to help search-and-rescue teams and other emergency responders at night. Other planned uses include bathing crops in sunlight, replacing broken streetlights and even providing solar power for military operations, all summoned by the tap of a button on an app.

“Search-and-rescue teams are expected to be our first customers, so this was a real-world test conducted alongside teams who would use our technology,” said a spokesperson for Reflect Orbital, which partnered with a local search-and-rescue team for the demonstration.

“We’ll keep working closely with local communities and authorities wherever we operate, and are excited to show how this technology can help save lives.”A coalition of environmentalists and astronomers are far less excited about Reflect Orbital’s ambitions, however These groups have criticized the company and the FCC for threatening a harmful change to the separation of night and day that will affect everything from people’s sleep to wildlife and the ability to see the stars from Earth.

“This is an idiotic project,” said Jan Hasselman, a senior attorney with Earthjustice, an environmental group. “There are a huge number of unresolved questions and significant potential impacts. Literally all of life on Earth evolved based on the rhythm of day and night, and there is a ton of data showing that messing with this is not a good idea.”

“There needs to be some sort of discussion and analysis before we grant these people the right to fundamentally alter the night sky,” he added. “The proposal for 50,000 of these satellite mirrors is crazy and would really end the night sky as we know it.”

“Some people are promoting the already unhinged idea of installing space mirrors facing away from the Earth… Imagine wanting to turn those mirrors around.”In August, four groups represented by Earthjustice asked the FCC to reconsider its approval citing concerns that opening up the skies to mirrored satellites, which would ascend to about 400 miles (645km) above the Earth’s surface before reflecting light back, would cause a litany of problems.

Animals such as birds, insects and mammals rely on the reliable change between day and night to feed, shelter and mate, with any change to this being potentially disastrous for some species.

Astronomers, meanwhile, have complained that this night-time glare would worsen existing light pollution and spur an overall rush to add more satellites to orbit—Elon Musk’s SpaceX plans to place 1 million celestial data centers around Earth—that will obscure the stars and cause more space debris that could descend as pollution back to our world.

There are also concerns that the scrambling of night and day will harm people’s health by disrupting their circadian rhythms as they sleep. Looking directly at the unusual glaring sunlight at night would also, much like doing so during a solar eclipse, harm people’s eyes.

Reflect Orbital has said its technology will actually aid the environment by boosting the energy output of solar panels when sunlight is pointed at them during nighttime, thereby reducing reliance on fossil fuels.

But some climate scientists have warned against meddling with the amount of sun’s energy reaching Earth. Proposals for solar geoengineering in which particles are sprayed into the atmosphere to deflect sunlight away from Earth instead of toward it, have also prompted fierce opposition“Global warming is happening because the Earth has a radiative imbalance due to the massive amounts of greenhouse gases we’ve dumped into the atmosphere,” said David Ho, a climate scientist at the University of Hawaii. “Some people are promoting the already unhinged idea of installing space mirrors facing away from the Earth to reflect the sun’s energy in order to decrease global warming. Imagine wanting to turn those mirrors around so that the Earth gets hotter.”

Reflect Orbital said it has had “substantive discussions” with scientists and astronomers on the use of its technology so that areas such as astronomical sites, national parks ,and other wildlife-rich areas are avoided.

“We welcome oversight and want to play a role in shaping it,” a spokesperson said. “We believe it is our responsibility to work alongside governments, scientists, and regulators rather than ahead of them.”