Lumen - Eternal Flashlight That Doesn't Need Batteries

This may be an expensive novelty product but the research and development assist in developing other thermo electric products.

It may not be suitable for larger applications but is a great idea. They are currently running a Kick Starter Campaign where iIcopied most of the material from. I thought it was a good story to follow on from my previous thermoelectric story today.


It is an ordinary flashlight with brightness comparable to your smartphone’s except 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:

Courtesy of Power Practical
Courtesy of Power Practical


As you understand, we can’t power really high-output led just with touching small TEG.

However, when your temperature is 98 °F and air temperature is 82 °F Lumen produce about 15 mA@3v. When difference is bigger – excessive power is stored in a capacitor to power Lumen whenever you need it. Such amount of energy is enough to power 5 mm Cree led with 3000 mCd light output.

Lumen in action
Lumen in action


  • Weight : ~ 35 gramms 1,2 oz for Aluminium version
  • Weight : ~ 45 gramms 1,5 oz for Titanium version
  • Dimensions: 40 mm x 10mm x 80 mm 1,6″ x 0,4″ x 3,2″
  • 5mm ultrabright CREE led
  • Light output: 3000 mCd
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mendozacortesIn The Journal of Physical Chemistry, Assistant Professor of Chemical Engineering Jose L. Mendoza-Cortes details how this new material efficiently captures sunlight and then, how the energy can be used to break down water into oxygen (O2) and hydrogen (H2). This process is known as oxidation, and it is also what happens during photosynthesis when a plant uses light to break down water and carbohydrates, which are the main energy sources for the plant.

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