Liter of Light is an open source design for a low-cost light tube that refracts solar light to provide daytime interior lighting for dwellings with thin roofs. Daylighting is cheaper than using indoor electric lights during the day. The device is simple: a transparent two-liter bottle is filled with water plus a little bleach to inhibit algal growth and fitted into a hole in a roof. The device functions like a deck prism: during daytime the water inside the bottle refracts sunlight, delivering about as much light as a 40–60 watt incandescent bulb to the interior. A properly installed solar bottle can last up to 5 years. History The use of plastic bottles in this way to provide indoor lighting from daylight was developed by Alfredo Moser of Brazil. Using the technology as a social enterprise was first launched in the Philippines by Illac Diaz under the My Shelter Foundation in April 2011. In order to help the idea to grow sustainably, Diaz implemented a "local entrepreneur" business model whereby bottle bulbs are assembled and installed by local people, who can earn a small income for their work. Within months, the organization expanded from one carpenter and one set of tools in one community in San Pedro, Laguna to 15,000 solar bottle bulb installations in twenty cities around the Philippines, and began to inspire local initiatives around the world. MyShelter Foundation also established a training center that conducts workshops with youth, business companies, and other groups who are interested in volunteering their time to build lights in their communities. In less than a year since inception, over 200,000 bottle bulbs were installed in communities around the world. Liter of Light had a goal to light up 1 million homes by the end of 2015. Technology description The Solar Bottle Bulb, as it has also been called, is installed in the roof of homes with the purpose of refracting sunlight in order to light up a room. The project's innovation lies in its utilization of cheap, durable and readily available materials to produce high quality natural lighting enabling the urban poor to have access to an affordable, environmentally friendly long-term alternative to electric light for use during the day. Most of the plastic bottles used are recycled 1.5 liter bottles. After being filled with water and a little bleach, the bottle is pushed through a steel sheet that serves as a