How can we mimic sunlight in closed rooms?

There are a few elements for that

• Spectrum – matching the full sun spectrum is the single most important factor. Currently LEDs exist even on Aliexpress that do the job; Note that possibly you don’t need the noon sun spectrum, which can be too bright and too white, and rather prefer some cloudy day or sunset.
• Light direction. The shadows create the feeling. The sunlight is directed, so you need some sort of reflector to collimate the LED light. But. The atmosphere scatters the blue, so the blue has to be diffused. Our eyes are actually sensitive to the shadow border and to the red tint on the edges. There are fancy nanotechnology solutions, but I think that diffusing mirror with blue filter does the trick just the same.

• Power. Sun power is not a joke. To reproduce it you need a lot of electricity. Half of the energy will go into heat – the LED actually has to be properly anchored to a radiator, and the hole thing is as much a heating device as an illumination one. Probably you need it in the cold winter anyway so you don’t mind very much. The air radiator size is just big enough to cool down in the room atmosphere a LED that produces similar intensity of light as noon sun. Maybe a little bit slow ventilation on the radiator is needed as well, but not water cooling. Again, consider reducing the intensity of your design, the eye has an exponential sensitivity, so you can decrease the power by an order of magnitude and experience it only as half as bright.

• Flickering. The LEDs need to be driven by good efficient drivers, in particular without a flickering effect that may be subconsciously unpleasant. The driver is going to be roughly the size of the radiator. The power supply for the driver is going to be of similar size as well.
• A full size “window” is going to be expensive and power savvy (though possible). Smaller installations with strategically placed colorful shiny objects under the direct sunlight can produce more interesting