Light tube with reflective material
”Also known as a "tubular skylight" or "tubular daylighting device", this is the oldest and most widespread type of light tube used for daylighting. The concept was originally developed by the ancient Egyptians. The first commercial reflector systems were patented and marketed in the 1850s by Paul Emile Chappuis in London, utilising various forms of angled mirror designs. Chappuis Ltd's reflectors were in continuous production until the factory was destroyed in 1943. The concept was rediscovered and patented in 1986 by Solatube International of Australia. This system has been marketed for widespread residential and commercial use. Other daylighting products are on the market under various generic names, such as "SunScope", "solar pipe", "light pipe", "light tube" and "tubular skylight".”
https://www.bbc.com/news/av/technology-45827812/mitsubishi-w...
"CoeLux systems combine LED lighting that reproduces sunlight spectrum, direction and brightness with optical systems and nano-structured materials that reproduce the endless distance of the sky and sun."
If it actually does reproduce the sunlight spectrum it'd have to have a very high CRI, no? Toshiba has their TRI-R LEDs claimed to be capable of 95% of the sunlight spectrum and they are rated at a CRI of Ra97. Yuji has LEDs with claimed CRI of 98, so it seems within the realm of possibility that these fake windows are very convincing.