WASHINGTON (REUTERS) - A small device could light up the lives - and screens - of 600 million cellphone users in the developing world.

Spark, which creates electricity from open flames, is the brainchild of students and graduates of Seattle's University of Washington, who have launched start-up JikoPower.

"We use a device, it's a thermoelectric material that generates electricity when there's two separate temperatures across its two faces. So we heat up one end in the fire and then have a water reservoir in the centre that keeps the other side of the material cool and, as heat flows through this, a temperature differential is created that induces a current through the material and which is electricity that we can convert and charge a phone with," said co-founder and engineer Aaron Owen.

Spark can generate up to two and a half watts of power, enough to charge a cellphone - a possible game changer for millions in the developing world who live without electricity.

"Everyone over there is using biofuel cook stoves, cooking six or more hours a day and, as engineers, we know that's a lot of heat energy being created and most of it just evaporates into the air. So if we can harvest just a little bit of that and turn that into electricity, we can actually provide really useful power that these people need," said Owen.

The company says it could also be popular in the developed world, with campers for instance - or in the event of a civil disaster or power outage.

JikoPower has launched a crowdfunding campaign.

Owen hopes the invention will ignite a spark of enthusiasm among investors, as well as users.