Light pipes (or sun pipes) are a means of providing sunlight to places it wouldn't otherwise reach. But they're not widely used - why is that?

I suspect it is because they're not a reliable means of illumination - on overcast days they may not provide enough light to work, and at night you'll need another light source anyway. Thus they tend not to be installed.

I propose that for large multiple-occupant buildings a more integrated approach would allow the effective use of sunlight where available, providing a decent reduction in electrical light usage.
A large light collector is installed in the building's roof. Because it's serving many rooms there are economies of scale, and it's probably worth using a sun-tracking device to increase the efficiency.
Inside the building, the light is split into separate streams which are piped to the appropriate rooms.

But here's the clever bit: the light drawn to each room is dependent on the need. There's a light switch (can be a dimmer switch if necessary) in each room, and the amount of light directed there is regulated dependent on that. Furthermore, when the sun is not providing enough light due to weather or being on the wrong side of the planet, electrical lighting is used to boost the supply.
Changing lightbulbs is necessary less often, since the system can accomodate a few broken ones (and they presumably get less use and switch on and off less frequently). Plus it's easier, since they're all in a central location.

If there is a surfeit of sunlight, the surplus could easily be redirected to the underside of a solar-thermal array, providing more hot water.

The building as a whole therefore uses less electricity. To deal with the human nature, there probably ought to be a charge dependent on the amount of light transmitted into the room. The rate be reduced dependent on the proportion of sunlight used, but would never be zero to prevent people demanding maximum illumination the whole time.
-- Loris, Mar 08 2010

like this :) Solar_20Lighting
[FlyingToaster, Mar 08 2010]

combined with Single_20Source_20House_20Lighting
[FlyingToaster, Mar 08 2010, last modified Mar 09 2010]

I'd <harrumph> noisily but it *is* such a great idea <links> (I've got the solar>light-tube bit and the one-stop-shopping for lamps as separate posts, don't remember why, exactly)

For your 5th paragraph, I've the (unposted) idea of using mirrors to split off anything above or below the visible spectrum to be used full-time for electrical or heat generation. And if you had a greenhouse you could split off the chlorophyll spectra as well.

But if you mean 20-storey apartment buildings by "multi-occupant", that obviously won't work since there wouldn't be much light hitting the roof to redirect inside. You could however replace quite a bit of corridor lighting needs.
-- FlyingToaster, Mar 08 2010


Would save on matches
-- pocmloc, Mar 09 2010


I'm pretty convinced that the reason light pipes arn't used much here is the variability of sunlight. I guess this does mean that this system would need a bank of small lights which would sometimes have to constantly switch on and off as clouds went past. Perhaps white LEDs would be useful for this.

I don't think there is any particular issue with "20-storey apartment buildings". Electric lights are much dimmer than sunlight, I found this on a random page on the internet:

"...average indoor lighting ranges from 100 to 1,000 lux, and average outdoor sunlight is about 50,000 lux."

This suggests that given 'average sunlight' (whatever that is), one could illuminate 50 to 500 times more internal space. Given that, the useful limit of sunlight transfer is somewhere between 50 and 500 storeys. Actually less, depending on transfer efficiency. But then again, that's assuming that every room is lit, which probably isn't the case.
-- Loris, Mar 09 2010


I've also considered this. One advantage that you forgot to mention is that you can justify a spectrum-accurate bulb or array that accurately replicates sunlight. These are typically a little bit expensive, brighter than you would want for one room, and not the most efficient.. but do provide the benefits of sunlight. Being able to run 1 and distribute the light would be nice.
-- AutoMcDonough, Mar 09 2010


// the (unposted) idea of using mirrors to split off anything above or below the visible spectrum //

Dash it, [FlyingToaster], that was just on the tip of my cerebellum. Prisms rather than mirrors though, shirley?

// a light switch / in each room, and the amount of light directed there is regulated dependent on that. //

That seems a tad bass-ackwards to me. If the occupant dials up the amount of light they require, the system should pipe in all the free sunlight available and top up with electric light only as required.

Overall, a [+]
-- BunsenHoneydew, Mar 19 2010


//Prisms rather than mirrors though, shirley?//
possibly cheaper I suppose, though the materials I was going through looking for "perfect" mirrors usually used a dye on a flat piece of glass, so light within the spectrum of the dye bounces whereas not, passes.

//bass-ackwards// what if more than one room's occupied in the building ?

(sorry'ish for hijacking your post, Loris)
-- FlyingToaster, Mar 19 2010


::// a light switch / in each room, and the amount of light directed there is regulated dependent on that. //
That seems a tad bass-ackwards to me. If the occupant dials up the amount of light they require, the system should pipe in all the free sunlight available and top up with electric light only as required.::

Erm, what? That's what I said.

I think you've skimmed the idea and misunderstood, Bunson me old mucker. The *switch* is in the room - having it elsewhere would be stupid. The top-up light source is shared, as I clearly stated.
-- Loris, Mar 19 2010



random, halfbakery