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.
top of the box just big enough to fit the bottle. I took another reading with just the hole. I got 4.13 fc.
on the ground and got 4,840 foot candles. Then I aimed directly at the sun and got 9,710 fc. So the low angle sun on the light meter was around half of the reading I got pointing directly at the sun. This matches the result I got with the solar soda bottle light. By the way, the sun is pretty bright isn’t it? Thousands of foot candles of light! Small wonder you can’t stare at the sun.