This is more of an experiment rather than a project but it teaches an important lesson about utilizing solar light in a building. It also teaches about the concept of refraction or light dispersion.
There have been some headlines lately about a light made from a two liter soda bottle that is solar powered. In a way, that’s true but a more accurate description is that of a simple but highly efficient skylight sometimes called a solar tube. It’s supposed to have been the brainchild of MIT students and is now actively used and installed by MyShelter Foundation throughout the Philippines and other countries.
The “bulb” is a typically a two-liter plastic bottle filled with purified water and some bleach which has its cap sealed on. The bleach prevents mold and bacterial growth in the water giving the bulb about a 5 year life-span. The bottle can be a two-liter, clear plastic soda bottle similar to that used by Pepsi or Coke. A hole is cut into the roof of the house (imagine a wooden box with a tin roof just above head height) and the bottle is inserted into the hole with the bottom of the bottle in the house and the cap end on the outside. A sealant is placed around the bottle where it penetrates the roof to seal out the weather. Just cutting a hole in the roof and covering it with plastic would just produce a beam of sunlight into the house. But when the sun hits the top of the bottle, the water inside uses refraction to spread the light throughout the room. They say it’s like having about 55 watts of incandescent lighting.
So why are they installing a soda bottle in someone’s roof? In the cities of the Phillipines, the houses of the poorer people are so close together that side windows still don’t let in any light so the houses are dark even during the day. This is an economical and safe way to get daytime lighting inside the house. Probably the most expensive part of the install, other than the tool to cut the hole, is the sealant. It’s safe because there are no candles to worry about tipping over and there’s less reliance on electrical wiring that is usually hazardous in poor areas such as this, if there is any electricity available at all.
The MyShelter Foundation is training residents on how to make and install the solar light bulbs through a program they call Isang Litrong Liwanag (“A Liter of Light”).
More information on this project can be found at: http://isanglitrongliwanag.org
There are also detailed instructions on how to make the light.
My experiment uses a 591 ml (20 oz) clear plastic bottle and a cardboard box to see if the bottle actually does draw light into the box.
This project, or experiment, does not imply that you should cut holes in your roof and install soda bottles, at least not if you can help it. Also, my test data can’t be used to scale up to a hut sized box. It’s not quite apples to apples here. The lesson learned is that if you want to look at the sky from inside your house, install a sky light. But if you want to light up the inside of your house using solar light, install a solar tube with good refractors built into it. A company called Solatube seems to be one of the leaders in this area. Just search on “solar tubes” for a lot more info.
Subject: Project #4 Solar Soda Bottle Light
With this project, will this be efficient if you use this in a room with lots of windows but could still use some more light? How much can it contribute? Does it still have an output of 55 watts? I would like to know as I would like to introduce it inside the public classrooms if would be a great help. Thanks!
As long as the sun can strike the top of the bottle, you should be able to get the 50 to 55 equivalent watts of incandescent lighting. Some things to consider are ceiling height and how far away the windows are from the center of the room. A high ceiling will reduce the effect of this type of light. For low ceilings, this type of light should work well. If the room is large and the center of the room is noticeably darker because of the distance from the windows, this light should help. If it’s not too difficult to install one, why not try it? Perhaps you could try one in another building like a storage shed just to see what the effect is from this type of light. Good luck.