In this maze of windowless tin shacks, school classes are often held outside because even in daytime it's too dark to see the blackboard. Now a youth group is hoping some 2-liter plastic bottles filled with water and bleach can brighten Kenya's slums.
The soda bottle-as-lightbulb was first discovered in Brazil by mechanic Alfredo Moser in 2002. In the decade since, tens of thousands of people who can't afford electricity or other sources of light like candles have converted to the water bottle lightpoint.
When the bottle is hung through a hole in the roof and filled with water and bleach, the bottle refracts sunlight and can produce as much light as a 50- or 60-watt bulb.
Veronica Wanjiru, 24, a mother of two, said even illegal electrical hookups, candles and paraffin are too expensive for many in the Korogocho slums.
Her 11-year-old and 5-year-old had to do their homework outside and in a rush before the sunset. Now that she has a water bulb, it can even produce light at night during a full moon.
"Before they put it in, my children would sometimes use candles, but after they have finished they would forget them on, which can even burn the house," she said.
The youth group called Koch Hope has been so successful in installing water bulbs for people like Wanjiru that it's now struggling to meet demand. The group installed the first 100 bulbs for free in April in hopes of attracting attention from donors and expanding the project.
Matayo Magalasia, one of the few people from the area to go to college, saw Moser's invention on the Internet last year and sought to replicate it. He approached a youth group known as Koch Hope about bringing light to Korogocho.
"I grew up here and I knew the houses were dark even during the day. I had to do my homework outside because we did not have light," Magalasia said.
Paul Jumbi, 28, a member of Koch Hope, said the group hopes to install the water bulb in every house in the slum and then expand to other Nairobi slums. Jumbi, though, said the project's expansion has been curtailed by a lack of money.
The plastic bottles are easy to find, but buying the sealant to put around the hole in the iron roof where the bottle sits is expensive.
Jumbi said their first attempts to install the water bulb were met with resistance from people who thought the hole would let in rainwater.
He and his team persuaded the owner of a primary school where students were being taught outdoors because they could not see the blackboard inside. Installing it in the school led other residents to buy in to the idea.
During electricity shortages in Uberaba, Sao Paulo in 2002, Moser discovered that hanging a plastic bottle full of water from his roof brought in extra light. The idea behind Moser's simple invention _ known in different places as solar water bulb or water bulb _ has spread to slum dwellers in at least three continents.
In the Philippines, a non-governmental organization is attempting to use the solar water bulb to brighten 1 million homes by next year. The project is known as "Isang Litrong Liwanag," which translates to "A Liter of Light."