Enlighten me, please

[Southwind17]

Is there something fundamentally different between artificial light, in its general and broadest sense, and natural light, or is light simply ... well, light?

[Ziggurat]

Is there something fundamentally different between artificial light, in its general and broadest sense, and natural light, or is light simply ... well, light?

The source of a photon makes no difference to the characteristics pf a photon. But photons come in different colors. The sun (which is what people usually mean by "natural light") gives off a characteristic spectrum. This spectrum is, in principle, reproducible by artificial means to within whatever tolerance you care for. In practice, however, any commercially viable light source you'll ever find will have a different spectrum than sunlight (meaning a different spread and ration of colors). Fluorescent lighting, in particular, tends to have sharp peaks and dips in the spectrum. Some people are more sensitive to these differences than other people, and it does cause colors to look different under different kinds of light. I've noticed, for example, that tomato paste looks darker under my fluorescent kitchen lighting than under sunlight, even compared to the red on the label of the can it's in.

[Southwind17]

The source of a photon makes no difference to the characteristics pf a photon. But photons come in different colors. The sun (which is what people usually mean by "natural light") gives off a characteristic spectrum.

Does this spectrum vary at the receiver depending on factors such as the time of day, atmospheric conditions (e.g. cloud cover), haze, etc? Is reflected moonlight the same as direct sunlight?

[Ziggurat]

Does this spectrum vary at the receiver depending on factors such as the time of day, atmospheric conditions (e.g. cloud cover), haze, etc?

Yes, because absorption and diffusion of that light varies with frequency, and the amount of atmosphere and what's in that atmosphere (like dust, smog, haze) vary depending upon angle of incidence and weather conditions. That's why sunsets are orange/red.

Is reflected moonlight the same as direct sunlight?

No, because the moon is not perfectly white (even though it looks fairly white to the naked eye). Its spectrum is different, but it's not likely special in the way that some people seem to hope (http://abcnews.go.com/GMA/OnCall/story?id=3983212). Is that what got you interested in the topic?

[Southwind17]

Yes, because absorption and diffusion of that light varies with frequency, and the amount of atmosphere and what's in that atmosphere (like dust, smog, haze) vary depending upon angle of incidence and weather conditions. That's why sunsets are orange/red.

So is this diversity of spectrum not likely to include the characteristics of most artificial "white" light, then?

No, because the moon is not perfectly white (even though it looks fairly white to the naked eye). Its spectrum is different, but it's not likely special in the way that some people seem to hope (http://abcnews.go.com/GMA/OnCall/story?id=3983212). Is that what got you interested in the topic?

Not at all. What got me interested was a comment by a reporter regarding that geeky guy in Austria who kept his daughter in the basement for 20 years. She emphasized that she, and three of her kids, had been kept under "artificial light", as though that was an added impediment. I understand that long absences of exposure to "natural" light is considered detrimental to the human body, so it just got me wondering what, exactly, the differences are.

The moon has only one meaningful purpose so far as I'm concerned, but so long as we have dairy farms I can't see any commercial viability in mining it! ;)

[Amapola]

Well, if someone is kept out of sunlight they might possibly suffer from vitamin D deficiency. Here is a wiki link: link (http://en.wikipedia.org/wiki/Vitamin_D). That might be one difference, and I suppose it could be fairly serious.

This is completely anecdotal, so get out your salt... we had a neighbor who kept a horse inside a dark barn its entire life, and the horse had ulcers in its eyes. I don't know what that was caused from, but that convinced me keeping a horse locked up in a dark barn is a very bad thing. :)

[rats]

The main difference between sunlight and artificial light is that artificial lights are designed to help us see, so they specialise in wavelengths in the visible regime. As we can't see in ultra-violet, lamps are not developed to radiate ultra-violet.

As Amapola pointed out, ultra-violet is important for the generation of vitamin D. However vitamin D can also be obtained from food sources such as fish so lack of sunlight may not have been a significant physical health risk with a decent diet.

[Southwind17]

As we can't see in ultra-violet, lamps are not developed to radiate ultra-violet.

Off the point a little, admittedly, but what about tanning beds?

[Primus]

From a practical point of view I notice the difference a lot. I've got very photosensitive eyes but bright artificial light (with the exception of camera flashes) isn't too much of a problem.
However even if its not that bright I can't go outside in anything resembling sunshine without dark glasses or it's a one way ticket to migrane town.

[CapelDodger]

No, because the moon is not perfectly white (even though it looks fairly white to the naked eye). Its spectrum is different, but it's not likely special in the way that some people seem to hope (http://abcnews.go.com/GMA/OnCall/story?id=3983212).

Oh my. Just when you think you've heard it all ...

[rats]

Off the point a little, admittedly, but what about tanning beds?
Yeah, I thought someone would pick up on that, glad to see you were more awake than me :) I was of course referring to household lamps used for normal lighting only.

[Cuddles]

There are also things like Seasonal Affective Disorder. Our body clocks rely to a certain extent on being reset by bright light. Artificial lights can apparently do the job, but the timing and variation in light level are also important. It may not sound particularly bad, but messing up your body's rhythm is likely to lead to sleep deprivation, and all kinds of horrible things can happen from that, especailly after 20 years.

[drkitten]

There are also things like Seasonal Affective Disorder. Our body clocks rely to a certain extent on being reset by bright light. Artificial lights can apparently do the job, but the timing and variation in light level are also important.

My understanding is that spectrum has something to do with it as welll; normal (yellowish) incandescants aren't as effective at treating SAD.

[Professor Yaffle]

http://www.lumie.com/help/research-abstracts/full-spectrum-light