Liter of Light is an open source design for a low-cost light tube (or deck prism or vault light) that refracts solar light to provide daytime interior lighting for dwellings with thin rooves. Daylighting is cheaper than using indoor electric lights during the day. The device is constructed simply, using a transparent two-liter bottle filled with water and a small amount of 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
Plastic bottles repurposed to provide indoor daylight lighting were first developed by Alfredo Moser of Brazil. The concept was introduced as a social enterprise in the Philippines by Illac Diaz through the My Shelter Foundation in April 2011. To promote sustainable development, Diaz implemented a local entrepreneur business model, enabling community members to assemble and install the bottle bulbs and earn income. Within months, the My Shelter Foundation expanded from a single carpenter in San Pedro, Laguna, to installing 15,000 solar bottle bulbs in twenty cities throughout the Philippines. This success inspired similar initiatives globally. The foundation also created a training center offering workshops for youth, businesses, and volunteers interested in building solar bottle bulbs in their communities. Within the first year, over 200,000 bottle bulbs were installed worldwide. In 2014, Liter of Light set a goal to illuminate 1 million homes by the end of 2015. In January 2015, Liter of Light received the Zayed Future Energy Prize in the Non-Profit Organization category. The initiative’s founder, Illac Diaz, was presented with the award during the Abu Dhabi Sustainability Week at the Abu Dhabi National Exhibition Centre. It was also selected as one of 120 Global Innovators for the EXPOLive Impact Innovation Grant program at EXPO 2020 in Dubai.
Technology description
The Solar Bottle Bulb, as it is also known, is installed through the roofs of homes to refract sunlight and illuminate interior spaces. The innovation consists in employing inexpensive, durable, and widely available materials to provide quality natural lighting. This offers a cost-effective and environmentally sustainable alternative to electric lighting during daytime, particularly benefiting low-income urban populations. The most common bottles used are 1.5-liter plastic containers. These are filled with water and a small amount of bleach to inhibit algae growth. The bottle is inserted through a hole in a corrugated metal roof and secured with a steel sheet acting as a lock to prevent slippage. Sealant is applied around the hole to ensure the installation is weatherproof. The water’s refractive properties diffuse sunlight, producing an omnidirectional light equivalent to a 40–60 watt incandescent bulb, depending on solar insolation. Installation instructions and material lists are publicly available online, supporting the spread of the technology through open-source principles.
Adhesive Selecting a durable, waterproof, and sun-resistant adhesive that effectively fills gaps is a key challenge in the installation process. Various local groups have tested different adhesives to balance cost and performance. Silicone-based and polyurethane adhesives have generally proven to be the most effective solutions. The inventor, Alfredo Moser, employed polyester resin to secure the bottles. Rigid glass bottles have also been utilized, and may allow easier sealing compared to flexible plastic bottles. Some sealants chemically interact with plastic, causing brittleness over time. Silicone-based sealants can form chemical bonds with glass, potentially enhancing the durability of the installation.
Countries
Argentina Liter of Light operates in Argentina through the NGO Litro de Luz. Volunteers train communities to install and maintain the lights in homes and streets, with activities in Buenos Aires, La Matanza, Rosario, and Córdoba, and support for projects in Peru, Venezuela and Ecuador. In 2019, the initiative won in the Sustainable Cities category at the sixth Latin America Verde Awards in Guayaquil, Ecuador, aiming to install about 400 systems per year to reduce waste and improve public health.
Bangladesh Liter of Light with Light Foundation based in Chittagong developed a local version of the bottle light called 'Botol Bati,' costing approximately $2 to 2.50 USD and lasting 4 to 5 years. The organization aims to promote awareness of bottle lights in remote areas by training local school students. Approximately 45% of the Bangladeshi population lack access to electricity, and about 24% live in slums where electricity is often obtained illegally. The Lights Foundation’s goal is to serve these communities.
Brazil
In Brazil, the project began in December 2012 when Alanna Sousa and Pedro Santos decided to implement Liter of Light in the country. In 2013, Vitor Belota, who happened to be Alanna's neighbor, was also motivated to introduce Liter of Light to Brazil after learning about the project in Kenya. The trio met and conducted a pilot project, installing the first daytime solutions in two communities in Santa Catarina. In 2015, recognizing that Brazilian communities presented distinct contexts and needs, the project began focusing on nighttime street lighting, carrying out its first installation in June of that year in the Vila Beira-Mar community, Rio de Janeiro. Since then, Litro de Luz Brasil has become an established non-profit organization that has directly impacted over 20,000 Brazilians through more than 3,700 installations, reaching upwards of 120 communities nationwide.
Chile Liter of Light began operating in Chile in 2015, installing 50 eco-friendly streetlights in Renca. The five-meter posts were built using bamboo, PVC, wood, and plastic bottles, fitted with solar panels and batteries lasting up to 28 hours. The project, carried out with support from CCU and the Festival Internacional de Innovación Social (FIIS), provided sustainable lighting for streets, a plaza, and a multi-purpose sports court, benefiting families without regular electricity supply.
China Liter Of Light China was created by three international students from China in 2016, and the first project in Rudong will be conducted in the early summer, 2017.
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