A decade ago, Katherine Lucey oversaw a heavily subsidized $1,500 solar-light installation in the rural district of Mpigi in central Uganda. The 60-watt rooftop solar panel system could power three lights in the four-room, off-the-grid house.

The family's father wanted the lights in his office, bedroom, and main room. But his wife successfully argued instead for a light in the room where she cooked dinner, a light outside for security, and a light for her chicken coop. After all, chickens lay more eggs when they have more light.

Lucey recalls being struck by how something as simple as light could profoundly change a family's life. Indeed, after solar-powered lighting was installed, the family prospered by selling more eggs and, over time, they bought a cow, a goat, and a pig. The woman even started a school and women's literacy club.

"It was such a simple, fundamental intervention," said Lucey, who now runs a solar lamp nonprofit called Solar Sister.

Today, solar lights are making similar differences in millions of lives in the developing world-at a fraction of what they cost when Lucey did the installation at Mpigi.

Thanks to technological advances, simple solar lamps go for as little as $10 to $20 each, and ones that have multiple brightness settings and an outlet to charge a cell phone don't cost much more. For daytime use, there are even cheaper options, such as a $2 to $3 solar bottle bulb made of a plastic bottle of purified water and bleach, sealed into the roof. The water helps disperse sunlight into a room, while the chlorine keeps mold from growing.

In wealthy countries, where access to cheap fossil-fueled electricity from the grid is nearly universal, solar electricity is still seen as an expensive energy option. That's particularly true when considering that a rooftop photovoltaic installation of sufficient size to power an electronics- and appliance-packed home costs tens of thousands of dollars. But the calculus is much different when bringing electricity for the first time to homes and communities that have none, with an aim of providing basic needs such as lighting and cell-phone charging. Development organizations are finding that solar energy is one of the most cost-effective options for providing not only power, but also a better livelihood.

Beyond Candles and Kerosene

Private companies and nonprofits are tapping into an enormous global need. An estimated 1.6 billion people, or more than one-fifth of the world's population, don't have access to a public electricity grid and instead rely on other means of lighting such as kerosene and candles. Nearly 600 million of the energy-poor live in Africa.

Buying kerosene fuel can strain already tight household budgets, often meaning little or no light for key evening and nighttime stretches when children could be studying and parents could be working indoors.

Kerosene also produces toxic smoke and soot, which damages lungs and causes other serious health problems. Kerosene lamps, especially makeshift ones, also are dangerous-tens of thousands of children and adults in the developing world die or are seriously burned in kerosene accidents each year.

It's unclear how fast the solar lamp market is growing, but India's 2011 census alone estimated 1.1 million homes with solar lighting devices.

Examples run the gamut:

The Scandinavian furnishings company Ikea has partnered with UNICEF and Save the Children to provide solar-powered lamps to tens of thousands of children in rural schools in India and Pakistan.

The International Organization for Migration provided thousands of solar lamp systems to people displaced by the 2010 earthquake in Haiti.

Nonprofit EMACE Sri Lanka has distributed 172 solar lamps to fishermen in Sri Lanka for night fishing.

A Philippines organization called Isang Litrong Liwanag (A Liter of Light) has helped install more than 30,000 solar bottle bulbs in mostly poor areas of the Philippines. On a sunny day, a one-liter bottle sealed into the roof of a shack refracts light at a strength roughly equivalent to that of a 55-watt light bulb. The bottle bulb was designed by students at the Massachusetts Institute of Technology, but the concept of a solar glass bottle reportedly was pioneered in Brazil by Alfredo Moser, a São Paulo mechanic who was seeking to light up his workshop.

"A solar bulb works at daytime only given that the sun is the source of light but is also useful at night if the moon is bright or if there is a source of light (nearby) for example a street lamp post," said Katrina Cardenas, A Liter of Light's internal affairs director.

U.S.-based d.light Design was one of the pioneers in distributing rugged solar lamps and lanterns, and now distributes its products in 40 countries, focusing particularly on Sub-Saharan Africa and India.

In just five years, the company has distributed more than 1.4 million lanterns, ranging in price from about $10 for a student lamp to about $45 for a rugged, handheld lantern with four light settings and cell-phone charger. A partnership with the Shell* Foundation is aimed at implementing market awareness programs and supporting local entrepreneurship.

Donn Tice, chief executive officer, said that while d.light is a for-profit company, it has a social mission to help people replace kerosene lanterns, cheap flashlights and other throwaway items with safer, cleaner, more permanent lanterns.

"These products really have to be rugged to survive and do their job in a developing-world environment," Tice said in a call from the company's Delhi office.

Atul Mittal, d.light's India marketing director, said a family can recover their cost within three to four months, based on buying a kerosene lantern for $2.50 and spending $3 a month on fuel.

Surveys conducted in India showed students increased their study time and received higher grades.

Toyola Energy in Ghana is known for selling energy-efficient cookstoves but is using the same network to sell solar lamps. In 2011, the company sold 5,453 solar lanterns and small home solar systems, mainly in northern Ghana but also some in nearby Togo and Nigeria, said co-founder Suraj Wahab. He expects those numbers to double this year.

A lantern with three light settings, a small plug-in solar panel, and a cell-phone charger goes for $30.

Wahab said Toyola Energy has found that the "very basic" lantern can change the lives of rural dwellers. "They have aspirations to live the good life like everybody else and are willing to pay for it," he said by email.

In fact, he said, some customers have paid for their systems by setting up businesses to recharge villagers' cell-phone batteries. In rural villages without public electricity, people have to scramble to find places and ways to recharge their cell phones.

From Light to Economic Development

The family in Mpigi, Uganda, who used solar lights to power their egg-selling business inspired Katherine Lucey to form a U.S.-based nonprofit two years ago called Solar Sister, which trains women as entrepreneurs who sell solar light products in Africa. ExxonMobil Foundation's Women's Economic Opportunity Initiative provided a key grant to launch a full-scale enterprise.

Solar Sister is targeting women, because they typically are the ones who manage household utilities. The nonprofit now has 143 entrepreneurs who have sold more than 3,500 solar lighting products in Uganda, Rwanda, and South Sudan, benefiting an estimated 17,600 lives. According to the industry rule of thumb, one solar lamp system will benefit an average of five people in a household.

Lucey is candid about the challenges, which include a heavy investment in training in part to bridge the technology know-how gap.

About 50 percent of the women interested in becoming entrepreneurs get through the first phase of the training, and only about 40 percent of those wind up doing well, she said. The others participate at a lesser level, perhaps selling a few lamps a month to supplement other incomes.

Solar Sister provides entrepreneurs with a "Business in a Bag," which includes a vetted supply of inventory, marketing materials, a ledger sheet, a bag and a T-shirt.

The organization also provides a variation of micro-credit. Products are provided up-front and entrepreneurs repay in 30 days, after they get cash from sales. "This allows them to start up a business without access to capital," Lucey said. "If they are unable to sell the product, they can return it for full credit."

A successful entrepreneur typically would sell 10 products per month at an average retail price of $45 (student lamps, lamp/phone chargers, a home system or two) and earn a 10 percent commission, or $45. That's $540 in annual income, at least in line with per capita income figures in Uganda.

Women participate at the level that suits their needs, Lucey said. "We have many who sell less, and are happy just to make $10 a month to make ends meet or pay school fees for the fifth child in the family, and a few who sell much, much more."

She gave the example of a woman named Grace whose husband earns $250 a year as a counselor for families of AIDS patients. Grace has been able to triple her family's income by becoming a Solar Sister entrepreneur. The family needs the money: Grace and her husband support 10 children, including six from relatives who died of AIDS. The additional income has enabled all of the children to attend school.

Lucey said market saturation isn't a problem at this point. For example, Solar Sister has a team of 15 entrepreneurs in Mityana, Uganda, which "looks like a typical rural community with dirt roads, mud-walled, thatched-roofed houses, and chickens wandering about." But that rural town has a population of 350,000 people, and is growing rapidly.

While the worst-case scenario for this type of enterprise is that an entrepreneur disappears with a small amount of inventory, the worst case Solar Sister has encountered came when a woman wanted to supplement her income from selling fish at a roadside market.

"It did not work out too well for her, the product was not a natural fit for her customers to say the least, and the lamps came back to us a little smelly," Lucey said. She said that prompted Solar Sister to institute a "must be returned in good condition" policy.