The daytime light which illuminates dark rooms in slum communities is made using only a plastic bottle water and 10ml of bleach (to prevent algae growing).
When the bottles are slotted into purpose-built holes in the roof they refract sunlight.
Diaz came across the idea first invented by Brazilian mechanic Alfredo Moser while studying at the Massachusetts Institute of Technology in the US.
For the night lights LEDs are wired to a miniature solar panel using the plastic water bottle as protective casing.
The light needs to be exposed to three to four hours of sunlight to last all night.
In the Philippines the Liter of Light team asks residents to pay $1 (60p) or less to buy the daytime light.
This is to ‘gain the people’s trust’ says Diaz.
He claims people can save up to $10 each month and the company will return after two months to ask if the customer wants to upgrade the water bottle light for between $3.78 for the most basic model to $56.70 for something brighter and more advanced.
Secrets of success
Liter of Light volunteers credit much of its success to its open-source online approach: designs and instructions are shared on YouTube and users can share advice and experience on social media.
Volunteers are also recruited online.
By enlisting people globally on the ground Diaz says he has created a model that can mould itself to the specific needs of each country.