Thread: Radiating light - Underground Greenhouse

Hi,

A first time poster, I have an idea for a building project, but I'm a bit stuck on the physics aspect of it and would like to know other people's opinions and ideas on how I can find a solution.
I've googled unfortunately to no avail.

I am looking for a way to project light downwards into a series of underground rooms.

I like the idea of being able to grow plants in each room, and would like for the bottom room to be lined with turf.

So my idea is this: I've seen chicken farmers put 2L coke bottles full of water into the roofs of chicken coops to reflect light into them.
This works really well, and I think I'd like something similar for the roof of my conservatory.

I've definitely got my work cut out for me, and think some sort of tetrahedral shaped glass blocks might do well at refracting the light down and out inside enough for the light to be carried to the bottom.

What ideas have you guys got on what I could use for the roofing?
As a chemistry student I'm not so well-read on physics, especially light, but think there must be a solution to carry the light down effectively.

I think there should be a way to focus the light downwards some way? But I'm not sure what to google for.

Look forward to hearing any ideas.

Thanks
Arius

I have seen these used for houses built under/into the ground: Light tube - Wikipedia, the free encyclopedia

They are pretty effective, as far as I can tell. I don't know what you can do to maximise the light gathered.

or
Just use solar cells to power electric "day" or "grow" lights.

..............
If you're going underground, how much area of above ground "light tubes" are you willing to allow?
Turf usually likes "full sun". True?

I like the idea of being able to grow plants in each room, and would like for the bottom room to be lined with turf.

Turf requires a lot of sunlight. I'm not sure how you could maintain healthy turf in an enclosed room in terms of soil and, particularly, flows of water through that soil, but I'd suggest walking before you run with maintaining plants in such an environment. Even if you're designing rather than building the thing.

If you can successfully grow traditional greenhouse plants, like ferns, that do best with diffused rather than direct light - then move on to growing herbs and salad greens in chosen places with the best light - then you can do some trials with patches of turf in the best growing conditions you can provide.

My own thought is that you'd do best with a plant that is often used as a turf substitute - dichondra is good, but doesn't work wonderfully well when people walk on it, in the circumstances you're talking about it would work pretty well as a vertical green wall. Green wall - Wikipedia, the free encyclopedia

Originally Posted by Arius

I think there should be a way to focus the light downwards some way?

Google "heliostat" - you would then direct the reflected light through a skylight, such that the focus was at or near the skylight and the light diffused beneath that point. You'd need a lot of light. Then you have the problems of cooling; 1000 watts/sq m is a lot of heat to remove from a room.

We have a lot of experience in British Columbia with "buried" grow operations, for marijuana. It's a quasi-legal enterprise so growers developed tricks to avoid detection. They defeat consumption analysis by power company, defeat helicopter infrared, suspicion by neighbours, etc. etc. Provincial exports are said to exceed fisheries and forestry combined, so this is a large mature industry with seasoned professionals doing genuine R&D. Look there for answers.