[jamespitts]

Artificial sunlight could be revolutionary if applied with scale in cities. It could enable new, far denser forms of architecture "built for people", mitigating the ill psychological effects of being without natural surroundings.

The energy use would be heavy, but it might be worth the cost given the transportation energy savings and higher productivity and happiness of the city population.

[jkxyz]

Don't forget seasonal affective disorder, or just the general influence on affects that cloudy weather has. Imagine waking up to streaming sunlight every morning. I can see that making a huge change in people's lives.

[seivan]

It would have to produce vitamin-D (or whatever the sunlight produces when it hits your skin) in order to combat that.

Source: Me in wintertime Sweden.

[sneak]

Concurrent orally-administered vitamin D would achieve the same effect.

[mful]

Do you have a source for that?

My understanding is that (a) utilization of dietary vitamin D is significantly lower than naturally produced D (from sun exposure) and (b) vitamin D is one of several micronutrients produced from sun exposure.

[jrapdx3]

> My understanding is that (a) utilization of dietary vitamin D is significantly lower than naturally produced D (from sun exposure)...

The end product of UVB irradiated skin (i.e., sunlight) is vitamin D3. (D3 is "activated" locally in tissues utilizing it.) Ingested D3 supplements effectively add to the body's supply, though the optimum intake is controversial and varies among individuals.

One difference between sunlight and supplements is that D3 production via UVB exposure has an upper bound, only so much can be made because there's a limited amount of substrate available in skin cells to convert to vitamin D. The upshot is sunlight is "safer" re: potential toxicity of excessive vitamin D intake.

AFAIK vitamin D is unique among nutritional factors in its reliance on UVB exposure. Don't know of any other micronutrients directly related to sunlight, but possible there's something I've overlooked.

[_0w8t]

It is unfortunate that "vitamin D" is called "vitamin" since it is in fact a hormone. As with most hormones, their effect depends on many factors including the number of receptors on target cells that can change significantly increasing or decreasing sensitivity to D. That itself is poorly understood and it is unknown how long-term consumption of D supplements in what ever form with little exposure to real Sun affects sensitivity.

So the advise is to take D supplements only if recommended by a doctor.

[erkkie]

Melatonin as well

[upofadown]

That presumes that artificial sunlight is actually desirable. One of the important functions of a building is to block the sun. Very few people would want to live/work in direct sunlight.

For circadian light you just need something that is sufficiently bright and blue. ... or just blue for that matter, blue LEDs are cheap and efficient.

None of this can improve surroundings that are otherwise unpleasant...

[jamespitts]

I think that sunlight is highly desirable, to an extent!

A building's function is to block unpleasant sun, but a window's function is to let it in and to control it. Artificial sunlight could enable more control over the sunlight factor.

Regarding circadian rhythm, it is not fully understood and blue light may not be the only important factor. Perhaps the visual sense that there is sunlight is also an important cue. But yes, blue light is clearly important. I would hope that any public lighting system would strongly take it into account.

For example, the color and feel should reflect what happens in the natural world! The LED lights being installed on city streets right now might cause problems for us (not to mention the blue light in our screens).

Unpleasant surroundings take a huge toll on people in cities. I am dismayed by the noise, pollution, lack of overhead cover, and threatening cars when I walk around SOMA and so many other places. A single tech like artificial sunlight won't cure all ills, but it is a tool that will help cities become larger and more livable.

Construction robotics, new materials, methods to better maintain plants and trees, and obviously transportation are also important tools in this fight.

[ogig]

But, can we really replicate sunlight? Might sound pessimist but the sun is a star, 1AU away, with a huge mass compared to earth, and It's the energy source for life here. Seems like a very long shot aspiring to create an artificial replacement for that, even for the narrow objective of tricking our bodys.

There must be some scientific knowdlegde regarding this that I ignore.

[contravariant]

Like you said, the sun is 1 AU away, we're getting a fraction of its energy. Actually that fraction is still way beyond what were able to generate, and will remain that way for quite some time. However, we only need to illuminate the part of the earth with humans in it, which is a more manageable scale.

What we consider sunlight is essentially the light emitted by any object at 6000K, which is reasonably easy to achieve but somewhat difficult to contain. And actually mimicking the sun is usually not the best method (for one, the unfiltered UV would be very unhealthy). It's possible to approximate the visible part of that light though, and we're gradually getting better at it.

[visarga]

If many people are going to live close together maybe we also need sound proofing to match the artificial skylight.

[jamespitts]

Sound management for all of the cars, drones, and (probably) robots might be even more important than sunlight!