A Liter of Light

SOLAR BOTTLE BULB
The solar bottle bulb is taking the developing world by storm bringing sustainable, affordable lighting to the underprivileged rural communities in a number of regions around the globe, the concept is cheap, simple and most importantly sustainable, but how did such an amazing idea come about?
The concept was first conceived in 2002 by Alfredo Moser, a mechanic in Sao Paulo, Brazil, to light his workshop when his neighbourhood was suffering energy shortages, enabling him to continue working. His neighbours, intrigued by the idea, soon started following suit, adding the bulbs to their homes in kitchens, bathrooms and living areas where electric light was prohibitively expensive and inefficient.
The bottle bulb revolution was then further enhanced by The “MyShelter Foundation”, which runs a program in the Philippines called “Isang Litrong Liwanag: a Liter of Light”. Based on a project developed by students at MIT under the Appropriate Technologies discipline, the project aims to bring sustainable, affordable lighting to the underprivileged rural communities in the country. A Liter of Light aim to bring light 1 million homes using this green technology not only in the Philippines but in shantytowns in India, Africa and other southeast Asian countries, by the end of 2012.
Solar bottle bulbs are usually made out of 2-L bottles, use no electricity and produce the same amount of light as a 50- to 60-watt incandescent bulb, there is no leakage and the bottles can stay there for years without any need for maintenance! The water bottle lights are said to last for 5 years.
The concept seems so simple but how does it work?
The lights work by refracting sunlight in a 360-degree arc around the room, which provides superior light to a window or skylight, only allowing light into a room in a direct beam. The bleach keeps the water clean and clear by preventing algae growth.

So what’s the science behind the concept?
When light moving through the air runs into a denser medium such as water, it changes direction because of refraction. The light beam “bends” when it enters the so that it’s travelling more directly down into water. That’s very helpful if you’re trying to get more light to go down through the bottle into a dark room below.
Despite this, 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. Without a solar bottle bulb, only a small amount of sunlight would be collected.

Compared to this is how much light you’ll gather with a solar bottle bulb.

Once the light is in the room, the bottle offers another major benefit. If you only have a hole, or 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.