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Building an artificial sun that looks realistic [video]

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Re: Building an artificial sun that looks realistic [video]

#121

Post by Animats »

EricE wrote: post #118
Animats wrote: post #83

Earlier quoted context omitted.

Use Fresnel lenses with a shorter focal length and reduce the depth. It would be useful to start with a standard home-type window from, say, Home Depot, and build a unit about 120mm deep using multiple shorter focal length Fresnel lenses.[1] Then, in a basement or windowless room, mount some of these into a wall. Add curtains. Nice if your home office or workshop is in a basement. This has commercial applications. Ho…

Keep watching the video - he builds Fresnel lens versions at the end of the video. The satellite dish is more dramatic so I don't blame him for leading with it :)

The idea is to build this as a light box behind a standard windowpane frame. Like this one.[1] With a 120mm short focal length, the unit only needs to be about 150 - 200mm deep, if you angled the optics so you get light at a 30 degree angle or so. (Horizontal sun rays would look wrong.) That's a convenient size; you could hang it on a wall, like a rather bulky picture.

[1] https://www.walmart.com/ip/Darice-Wooden-Window-Pane-w-6-Pan...

Re: Building an artificial sun that looks realistic [video]

#122

Post by dan-robertson »

joshspankit wrote: post #108
dan-robertson wrote: post #105

Earlier quoted context omitted.

Most things related to vitamin D are just correlation. If you are weak and frail you may not get out much and won’t have so much vitamin D. That doesn’t mean giving you vitamin D will make you strong. I heard that most studies don’t show benefits from vitamin D a supplements but maybe I’m wrong.

Sounds to me like what you heard could be easily proven/disproven by reading some studies.

I searched google scholar for “vitamin d meta analysis”. I skimmed the abstracts. These are some of the earlier results.

It seems supplements help but randomised controlled trials are needed: https://jamanetwork.com/journals/jamainternalmedicine/fullar...

“Vitamin D supplementation appears to reduce the risk of falls among ambulatory or institutionalized older individuals with stable health by more than 20%” http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.578...

Oral vitamin D supplementation between 700 to 800 IU/d appears to reduce the risk of hip and any nonvertebral fractures in ambulatory or institutionalized elderly persons. An oral vitamin D dose of 400 IU/d is not sufficient for fracture prevention. https://jamanetwork.com/journals/jama/article-abstract/20087...

High levels of vitamin D among middle-age and elderly populations are associated with a substantial decrease in cardiovascular disease, type 2 diabetes and metabolic syndrome. If the relationship proves to be causal, interventions targeting vitamin D deficiency in adult populations could potentially slow the current epidemics of cardiometabolic disorders. https://www.sciencedirect.com/science/article/abs/pii/S03785...

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At this point I got bored of looking at results (I omitted a few which only looked for correlations).

So while there is some evidence of some benefits for some people, I didn’t find evidence of vitamin d being the magic panacea that it sometimes feels it is claimed to be by people on the internet.

Re: Building an artificial sun that looks realistic [video]

#123

Post by def_true_false »

dan-robertson wrote: post #122
joshspankit wrote: post #108

Earlier quoted context omitted.

Sounds to me like what you heard could be easily proven/disproven by reading some studies.

I searched google scholar for “vitamin d meta analysis”. I skimmed the abstracts. These are some of the earlier results. It seems supplements help but randomised controlled trials are needed: https://jamanetwork.com/journals/jamainternalmedicine/fullar... “Vitamin D supplementation appears to reduce the risk of falls among ambulatory or institutionalized older individuals with stable health by more than 20%” http://c…

Well, if it may have benefits and costs pretty much nothing, it would make sense to take it...

Re: Building an artificial sun that looks realistic [video]

#124

Post by konjin »

konjin wrote: post #25
bukka wrote: post #4

I'm curious if the lack of heat in the lightrays will ruin the immersion of sunlight? Perhaps couple this with an IR heatlamp to add the real feel of sunrays hitting your skin?

The main issue is the blue scattering. If you can get away with pre-scattering the light before it hits the dish adding an IR lamp is no issue since you're using a parabolic mirror which has no diffraction. I have no idea if it 'feels' right doing that though. For full immersion you would also want a number of different light sources since leds are have very narrow spectra.

To answer anyone looking at this now: the Rayleigh scattering needs to produce diffuse light [0]. Which actually makes the project easier to pull off since you just need to place secondary lights all around the roof and walls of the room that emit AM1.5 diffuse light globally and not worry about any sort of filtering on the main light, which you need to match to AM1.5 direct.

[0] Applied Photovoltaics, Earthscan Publications, 2007: http://www.eng.uc.edu/~beaucag/Classes/SolarPowerForAfrica/B...

Re: Building an artificial sun that looks realistic [video]

#128

Post by hinkley »

throwaway9d0291 wrote: post #97
hinkley wrote: post #64

Why do fresnel reflectors seem to be so hard to find? Seems like they’d be a good option here.

Interestingly, you can DIY that too: http://www.dr-iguana.com/prj_FlatPackMirror/index.html And I think they really could be a good option. Unlike the lenses, there would be no chromatic aberration with a reflector, right? Plus, you can set the focal length to whatever you want (taking practicality into account of course). I might have to try it out...

If you could find two parabolic mirrors with a focal length difference of less than a couple of inches, I suspect you could take the middle of the short focus one and the outside of the longer focus one and stack them concentrically, to get a flatter dish.

Honestly for this use case, just sliced and stacked a single dish would give you mostly-collimated light, right? If you put this behind a mild diffuser you could probably still trick your brain unto thinking it's sunlight coming through the curtains.

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