Kevin Warnock

Entrepreneurship, ideas and more

Litre of Light – nearly free solar lights made with plastic water bottles and bleach

with 12 comments

Sometimes I learn of an idea that shocks me with its brilliance.

Today I will describe such an idea. It’s called the Litre of Light.

Here’s the summary from the project’s website, Isang Litrong Liwanag, which translates to ‘A litre of light’:

“Isang Litrong Liwanag (A Liter of Light), is a sustainable lighting project which aims to bring the eco-friendly Solar Bottle Bulb to disprivileged communities nationwide. Designed and developed by students from the Massachusetts Institute of Technology (MIT), the Solar Bottle Bulb is based on the principles of Appropriate Technologies – a concept that provides simple and easily replicable technologies that address basic needs in developing communities.”

A Solar Bottle Bulb is a clear water or soda bottle filled with tap water and a little bleach. This bottle in embedded into the roofs of houses, with part of the bottle outside, and part of it inside. There is sealant around the hole to keep the roof weather proof. When the sun hits the outside part of the bottle, a lot of light reaches the inside part of the bottle. The water inside the bottle makes the light omnidirectional, mimiking an electric light bulb. The bleach keeps the water clear for years. Without the bleach, the water would quickly turn green with algae. Without the water, there would be a bright spot on the floor, surrounded by relative darkness.

Each Solar Bottle Bulb produces about as much light as a 60 watt incandescent light bulb, according to the video transcript linked to in this sentence.

Solar Bulb installed and 'on' (picture from

Solar Bulb installed and 'on' (picture from

I wish I could take my Canon 5D Mark II into some houses with these bulbs installed and get some really high quality still photographs and video, to help spread the word about this really bright idea. Light bulb entrepreneur and proponent Thomas Edison would be pleased.

On the right, Alfredo Lim, the mayor of Manilla, Philippines, holding a litre of light 'bulb'

On the right, Alfredo Lim, the mayor of Manilla, Philippines, holding a litre of light 'bulb'

The beauty of the Solar Bottle Bulb is that it works and it’s really affordable, at about P150 to P200 (USD $4.66 at today’s exchange rate) per home, installed, according to Alfredo Lim, the mayor of Manilla in the Philippines, pictured above on the right. That 150 to 200 peso cost is per home, not per bulb.

I am going to install these in any eco home I build down the road. I have a big collection of glass bottles to choose from. I’m not sure if glass is as suitable as plastic, but I would prefer to use glass if it can be made to work reliably.

Written by Kevin Warnock

July 17th, 2011 at 5:00 am