This is a really simple solution to a serious problem.

http://www.bbc.co.uk/news/world-asia-pacific-14967535

Shame it only works during the day, but light is light.

That's actually rather cool.

I've seen houses on grand designs that use a similar (but much more expensive) approach.

On Grand Designs they used a polished aluminium pipe about 30cm in diameter with a weather proof covering over the top and a diffuser on the bottom. It brought a hell of a lot of light into the room.

I've seen that a few times too. I think one in particular one was one built into the side of the hill and therefore the back rooms on the lower floor were almost pitch black. The piping lit the place up, like you say.

I wonder what it does for heat escaping at night/in the winter?

But it's a really cool concept, I think it should be employed in more offices, and especially in schools.

It's a relatively small gap, about the same as a tube chimney, and it's not actually 'open' as such either. You're going to get less heat lost through a bottle of water than, well, a hole. I don't think that's a showstopping drawback.


Jon

That's superb. The best ideas are the simplest.

Considering the roof was only a millimetre of corrugated iron or asbestos with no insulation, I don't think it'll have a significant contribution to the heat loss at all.

Her assertion that it gives "about 60 watts of light" must have been false by the way. It possibly gives a light output similar to that of a 60 Watt incandescent bulb which is a very different story. You only get 100Watts / square foot of solar energy in strong direct sunlight, and most of that is not in the visible spectrum anyway. I'm just surprised more people didn't have skylights of some sort already - we're not talking expensive, high-tec or even rain-proof here.

Indeed, I did wonder why don't they save a bit of money and just buy the bottle. Cut it open into a square and make a whole for it to go in. I'm not sure but I imagine it would provide a similar amount of light?

Actually, probably not. There are various ways in which the bottle might 'capture' more light that a simple hole would. Depends exactly on the optical properties but it's quite probable the bottle acts as as prism depending on the refractive indexes of water and the plastic itself and a few other things. It's far too late to figure it out now tbh .

Jon

You can't "capture" more light than the exposed part of the bottle facing the sun.

If the light-pipe is 100% efficient with half in and half out of the horizontal roof and simplifying the bottle to a cylinder of height H and circumference D, then if the angle of the sun to the horizon is Z and we ignore environmental specular reflections we can compare thus:

A flat "Skylight" made from the same bottle has area HD and thus captures XHDsinZ where X is the brightness of the sun.

Light-pipe captures a vertical area component of HDcosZ/2pi plus a horizontal component of DDsinZ/4pi

Drawing the graphs in your head, you see that when the sun is high the skylight is much brighter. When the sun is low, the light-pipe is much brighter. Over all, their solution offers more even lighting for more hours of the day.

Also, when the sun is high, the light will actually fall through the hole onto a very small space below and the rest of the room would still be in darkness. It looks from the video like the internal half of the bottle scatters the light somewhat. So it's not quite as bright but the illumination is more general.

Jon

I guess the ideal solution would be a bottle of water and reflective material inside the room to bounce any light as much as possible.

Sod the physics its a brill idea ......