CoeLux tricked eyes and cameras into seeing a real skylight by simulating the atmosphere

Hospitals, offices, gyms and underground parking are full of rooms that never see daylight, and the standard fix is a bright lamp that mimics the sun's color temperature. CoeLux, an Italian company, argued that this is why artificial light still reads as artificial: a bare bright panel is a sun with no sky around it. To make light feel as if it were falling through a skylight, the company concluded, you cannot just simulate the sun — you have to recreate the atmosphere as well.

CoeLux's fixture combines LEDs with a thin coating of nanoparticles engineered to reproduce Rayleigh scattering, the same physical effect by which air molecules scatter short wavelengths and make the sky blue. A concentrated warm beam plays the sun, while scattered blue light around it plays the atmosphere, delivering the full optical signature of a real skylight rather than a flat white panel. The company's point was that color temperature alone was not enough: the quality and spatial structure of the light had to feel the same too.

People who experienced the skylight were fooled into believing there was an actual hole in the ceiling, and the sample photographs on CoeLux's site carry a note saying they are real and unretouched, not computer renderings. PetaPixel's February 2015 report described the physics, the pricing, and the intended markets of hospitals, gyms, offices and underground parking, with studio photographers as a possible future buyer once the price fell. A unit cost about £40,000 (~$61,000) at the time, plus up to £5,000 (~$7,600) for installation.

It works because the trick is not a clever image on a screen but the actual scattering process that daylight performs in the sky. The brain reads daylight from the pairing of a bright sun disc and the blue light scattered around it, and a camera meters the same optical reality, so both are fooled by the same physics.

Recreate the sky along with the sun: scatter LEDs through a nanoparticle layer the way air does

Matching color temperature alone leaves light flat; the eye reads daylight from a bright sun disc paired with blue scattered sky.

Recreating the real scattering process makes the effect physical rather than perceptual, so humans and cameras converge on the same verdict.

Rayleigh scattering is a known, controllable law, which turned a subjective design goal into an engineering spec.

The claim was checkable — unretouched photos and fooled visitors — before a buyer committed £40,000.

To reproduce a perception like daylight, copy the physical cause, not its visible features — then humans and sensors independently arrive at the same verdict.

PetaPixel's February 2015 report spread the demonstration widely, and a Hacker News post drew 276 points and 81 comments in February 2016, with discussion centered on the optics and the price. CoeLux said future versions would let the sun's position move within the frame and shift color temperature dynamically, pushing the product from a fixed fake skylight toward controllable daylight. The report records no sales figures, only the purchase price and installation cost that defined the product's early market.