Lumen flashlight doesn’t need batteries. It convert the heat of your body to produce light.
A flashlight with brightness comparable to your smartphone’s. His main feature – it doesn’t need batteries and virtually eternal.
Lumen has relatively simple work principle – you touch TEG (Thermoelectric Generator) – small ceramic bar that can produce electric current when we provide temperature difference between upper and lower parts of TEG.
In my application difference between temperature of your body (about 98 °F) and environment (at least 82 °F) is enough to generate power for single led. Metal body of Lumen serve as a radiator.
To better understand the main principle look at diagram: