After disasters like hurricanes Harvey and Irma, the lights often go out.
That can mean turning to candles or kerosene lamps, which can be dangerous, or flashlights with batteries that can be scarce and expensive. Around the world, consistent access to power is a problem worsened by hurricanes, earthquakes and monsoons.
So in 2010, after seeing the destruction caused by the earthquake in Haiti, Columbia architecture graduate students Andrea Sreshta and Anna Stork decided to take on the problem of darkness.
"We were just thinking there had to be a better alternative," Andrea Sreshta tells CNBC Make It.
In 2011, the pair launched Chicago-based company LuminAID, which sells a portable, waterproof light that packs flat and can be recharged with solar power. They built the first 50 prototypes by hand and were granted a utility patent.
Now, Sreshta and Stork are putting their invention to use in their own backyard. There are 2,500 lights headed to victims of Hurricane Irma, and after Hurricane Harvey, the company shipped 1,500 lights to Texas, enough to illuminate about 4.5 football fields.
They also sent some of their new product — a solar light that also has a waterproof phone charger — to members of the Cajun Navy, a group from Louisiana that drove in to help Harvey victims.
"That is a good example of a group in a disaster that really relies on their phones to stay in touch," she says. "Obviously they are not necessarily connected to an outlet where they can charge up, and the fact that our chargers are waterproof was very useful to them."
For Sreshta, who is from Houston, the project was especially personal.
"I was in total shock," she says. "My parents' house was flooded. Luckily, they had a different place to go that was higher up." The LuminAID team was also upset by news of her parents' flood, since their garage was the company's first warehouse in its earliest days.
LuminAID got its big break in 2015, when the co-founders appeared on ABC's "Shark Tank." The pitch won offers from all five sharks, but Sreshta and Stork picked Mark Cuban's — $200,000 for 15 percent equity in the company, with an option to lead the company's next round of financing with $300,000. Since the show, revenue has tripled.
Here's how the business works: One side is focused on aid, selling the product to non-government organizations, humanitarian groups and disaster relief organizations, which distribute them to people in need, like Syrian refugees and flood victims in Peru.
The company also sells its product to outdoor enthusiasts who can take the portable light with them camping, hiking or boating. For these customers, they sell the light in retailers like R.E.I. through Amazon and on their website.
Since Sreshta and Stork realized that people buying the lights for recreational uses were also interested in contributing to the aid mission, they started project "Give Light Get Light" the same year they launched the company.
"It's kind of the one-for-one model," she explains. "It has been really nice to be able to tie the two things together."
An individual LuminAID light retails for $19.99. Currently, for $29.99, shoppers can buy the "Give Light, Get Light Package: Hurricane Relief," which includes donating a light to someone else, according to the company's website.
That program has helped raise money, along with corporate sponsors, for the lights going to hurricane victims.
"Then we also just donate some ourselves," Sreshta says. To get the lights to the people who need them, LuminAID partnered with Missouri based non-profit Convoy of Hope, which responds to disasters in the U.S. and abroad.
While most of the time investors are focused on keeping costs low, Sreshta notes that Cuban was totally on-board to give away product.
"He emailed me right away and he said 'update what are we doing,'" she says. "It is good to know that as an investor you have that support because in this case sometimes we are just giving stuff away, and I don't know that every investor feels that way about the businesses they invest in, because typically it is about the bottom line."
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Disclaimer: CNBC owns the exclusive off-network cable rights to "Shark Tank." This story has been revised and updated.