Buzz Blog

Solar Bottle SuperHero

Thursday, September 15, 2011

Solar Demi is a man who travels around installing solar bottles in order to bring light into homes in some of the poorest neighborhoods in the Philippines.

It's amazing to me that there are places where even minimal lighting is a luxury. I'm glad to see that basic physics principles are bringing a little sunlight into the dark days of some impoverished Filipinos. (Of course, if you feel like sending a donation to the cause, you can help spread the light and the love a little further.)

I've seen a lot of speculation about how, and even whether, solar bottles can light a room so well. The fact is, they do work, and they rely on some pretty nifty physics to do it.

To begin with, cutting a hole in your roof will let some sunlight in. Even a small hole in a darkened room can make a big difference. There are, however, some problems with a simple hole.

Besides letting in the rain and insects, you only get as much light as falls directly through the hole. As Solar Demi knows, you can do much better than that with some grassroots engineering. Putting a water-filled container in the hole collects more light due to two fundamental optical effects: Snell's Law and total internal reflection.

When light moving through the air runs into a denser material like water, it changes direction. That is, the light beam kinks where it encounters the water surface so that it's traveling more directly down into water. That's very helpful if you're trying to get more light to go down through the hole.

Despite the help that Snell provides, some of the light will still be on a path to the opposite side of the cylinder. A portion of the light is trapped in the cylinder because of simple reflection, which can happen anytime light passes from one transparent material to another. However, during much of the day, the light will strike the cylinder walls in such a way that lots of light will be reflected down toward the hole. This is called total internal reflection. Light reflected this way will bounce back and forth as it travels down through the water column, much like signals passing through an optical cable.
A laser beam trapped in a plastic illustrates the effect well.

So, without a solar bottle, this is all the sun light you can expect to collect.

After Solar Demi gets through with your roof, this is how much light you'll gather.

Once the light is in the room, the bottle offers another major benefit. If you only had a hole, or even a small glass window, then sunlight passes straight through, and illuminates a spot on the floor or wall, like this . . .

Because of multiple reflections and different paths caused by Snell's Law refraction and internal reflection, light spreads out as it passes through the water column. That's what made the bottles appear to glow in the video of Solar Demi doing his stuff.

In the first of these two sketches, sunlight passes directly through hole. In the second sketch, I've added a few of the paths the light can follow as a result of the water column. There are actually an enormous number of possible paths the light can take, which results in an apparent overall glow, much like a light bulb.

All in all, it's a simple, clever, cheap, and environmentally sound lighting solution. In fact, I'm so impressed that I think I'll go donate right now.
Posted by Unknown


Charlice said...

Just came across this while searching for information on baby bottles. Although this isn't entirely related, but now I can see how this is going to benefit moms especially those still new to parenting and not experienced at all.

Monday, July 29, 2019 at 12:30 AM

rash said...

Does the baking soda can be a replacement of bleach?

Sunday, January 7, 2018 at 2:43 AM

Anonymous said...

greatest limitation is this system has no storage for use during the night. any one with some innovative ideas on appropriate storage?

Tuesday, January 17, 2017 at 3:42 PM

Anonymous said...

what if the plastic bottle melt? i mean if it's exposed to sunlight often there is a big chance that the bottle might melt or deformed

Tuesday, October 25, 2016 at 9:16 PM

jay jack said...

There is a floor above my place. Can I make a long tube with some turns, fill with water and bleach? If the top end is exposed to the Sun and the lower one inside my room -will the refraction work?

Friday, June 3, 2016 at 6:29 AM

brittanycasas said...

does it work at night

Thursday, January 14, 2016 at 12:58 PM

Muhammad said...

why dont you just add normal water like nestle, tap water is dirty so solar demi, maybe you want to look forward to that, I know you are not the solar demi but if you see him on the streets, tell him i said that.

Friday, December 4, 2015 at 12:46 AM

Anonymous said...

Just so it is pure and doesn't get cloudy over time. Tap water has lots of crap in it.

Monday, November 23, 2015 at 10:09 AM

Anonymous said...

why do we need distilled water rather than tap water?
whats in the distilled water?

Saturday, November 14, 2015 at 9:30 AM

Anonymous said...

If the bottle cap is not properly sealed then the water will vapourised.

Monday, September 29, 2014 at 11:07 AM

Anonymous said...

It does't works at night. It only tranfer outdoor sun light to inside the room. it is simple as like utter or a hole in a roof, The difference is that it spreads the lite in more direction, while a hole to one direction.

Tuesday, June 10, 2014 at 2:31 AM

Anonymous said...

does these stuff work at night because i am doing this project, if i show my teacher she will ask me questions then she will turn off the light

Saturday, April 12, 2014 at 1:43 PM

Anonymous said...

Distilled water and bleach are used to retard the growth of algae. There is no additional refraction with their use.

Friday, April 4, 2014 at 10:27 AM

Anonymous said...

can we use some other liquid instead of water which will give more efficient results ?

Wednesday, February 19, 2014 at 2:04 AM

Anonymous said...

Is there a good way to use these in colder climates? I intend to use them to add some light to an off grid basement, yet the fear of freezing is a concern. Would adding salt negate the reflective properties? would these also assist with hydroponic growing? An underground grow room would allow a much earlier start for my tomatoes. Do green bottles (Mountain Dew) work as well?

Sunday, February 16, 2014 at 8:08 PM

Chloe said...

It's for people with no windows. I thought that much was obvious.

Friday, January 31, 2014 at 9:40 AM

Michael Estill said...

Has this follow-up experiment ever been conducted? Currently examining the possibility of implementing this technology in various places in Guatemala, but a contrast with transparent roofing material (readily available but costly here) would be great to have.

Wednesday, January 22, 2014 at 5:24 PM

Anonymous said...

why are we using only distilled water?

Sunday, November 17, 2013 at 12:19 PM

Anonymous said...

Its a great idea and am very impressed. But if it only works at night whats the point ? Maybe to light up your basement or a cave. Maybe they used this idea in Egypt ?

Friday, November 15, 2013 at 2:55 AM

Anonymous said...

No. It cannot work at night. It transfers daylight from above the roof to the room below.

Friday, October 18, 2013 at 6:48 PM

Anonymous said...

Does it work at night???

Saturday, September 7, 2013 at 4:40 AM

Anonymous said...

try clear flakes or reflectors inside the bottle glue them or whatever also maybe quartz or tin of some kind maybe it might bounce the light in more directions or use Lk gell it should be the same concept i think idk just a thought and i say this because any clear liquid or bottle you hold up to the light it does it u can do different colors for decorative purposes by using food coloring Lk i did this at my grandfathers house his tool room is dark even in mid day so i put these in and now we have light everywhere now

Tuesday, September 3, 2013 at 10:17 PM

Anonymous said...

The light which is given out is too less how can we improve the quantity of light.....It does not lighten the room its very dim..

Tuesday, July 23, 2013 at 10:34 AM

Anonymous said...

Can this be improved to help in Urban city Where like in apartments.
Like, Fitting this light receiver at terrace which collects and transfer light through optic fiber to the respective floor.

Friday, January 11, 2013 at 12:39 AM

Buzz Skyline said...

I did.


Monday, December 17, 2012 at 10:35 AM